\documentclass{report} \usepackage{graphicx} \usepackage{color} \usepackage[colorlinks,urlcolor=blue,linkcolor=black,citecolor=blue]{hyperref} \begin{document} \title{Metasploit 3.0 Developer's Guide} \author{skape} \begin{titlepage} \begin{center} \huge{{Metasploit 3.0 Developer's Guide}} \\[150mm] \rule{10cm}{1pt} \\[8mm] \small\bf{skape} \\ \small\bf{mmiller@hick.org} \\[4mm] \textit{Last modified: \small{11/24/2003}} \end{center} \end{titlepage} \tableofcontents \setlength{\parindent}{0pt} \setlength{\parskip}{8pt} \chapter{Introduction} \par The Metasploit framework is an open-source exploitation framework that is designed to provide security researches and pen-testers with a uniform model that allows for the rapid development of exploits, payloads, encoders, NOP generators, and reconnaissance tools. The framework provides exploit writers with the ability to re-use large chunks of code that would otherwise have to be copied or re-implemented on a per-exploit basis. To help further this cause, the Metasploit staff is proud to present the next major evolution of the exploitation framework: version 3.0. \par The 3.0 version of the framework is a re-factoring of the 2.x branch which has been written entirely in Ruby. The primary goal of the 3.0 branch is to make the framework easy to use and extend from a programmatic aspect. This goal encompasses not only the development of framework modules, such as exploits, but also to the development of third party tools and plugins that can be used to increase the functionality of the entire suite. By developing an easy to use framework at a programmatic level, it follows that exploits and other extensions should be easier to understand and implement than those provided in earlier versions of the framework. \par This document will provide the reader with an explanation of the design goals, methodologies, and implementation details of the 3.0 version of the framework. Henceforth, the 3.0 version of the framework will simply be referred to as \textit{the framework}. \section{Why Ruby?} \par During the development of the framework, the one recurring question that the Metasploit staff was continually asked was why Ruby was selected as the programming language. To avoid having to answer this question on an individual basis, the authors have opted for explaining their reasons in this document. \par The Ruby programming language was selected over other choices, such as python, perl, and C++ for quite a few reasons. The first, and primary, reason that Ruby was selected was because it's a language that the Metasploit staff enjoyed writing in. After spending time analyzing other languages and factoring in past experiences, the Ruby programming language was found to offer both a simple and powerful approach to an interpreted language. The degree of introspection and the object-oriented aspects provided by Ruby were something that fit very nicely with some of the requirements of the framework. The framework's need for automated class construction code re-use was a key factor in the decision making process, and it was one of the things that perl was not very well suited to offer. On top of this, the syntax is incredibly simplistic and provides the same level of language features that other more accepted languages have, like perl. \par The second reason Ruby was selected was because of its platform independent support for threading. While a number of limitations have been encountered during the development of the framework under this model, the Metasploit staff has observed a marked performance and usability improvement over the 2.x branch. Future versions of Ruby (the 1.9 series) will back the existing threading API with native threads for the operating system the interpreter is compiled against which will solve a number of existing issues with the current implementation, such as permitting the use of blocking operations. In the meantime, the existing threading model has been found to be far superior to a forking model, especially on platforms that lack a native fork implementation like Windows. \par Another reason that Ruby was selected was because of the supported existence of a native interpreter for the Windows platform. While perl has a cygwin version and an ActiveState version, both are plagued by usability problems. The fact that the Ruby interpreter can be compiled and executed natively on Windows drastically improves performance. Furthermore, the interpreter is also very small and can be easily modified in the event that there is a bug. \par The Python programming language was also a language candidate. The reason the Metasploit staff opted for Ruby instead of Python was for a few different reasons. The primary reason is a general distaste for some of the syntactical annoyances forced by Python, such as block-indention. While many would argue the benefits of such an approach, some members of the Metasploit staff find it to be an unnecessary restriction. Other issues with Python center around limitations in parent class method calling and backward compatibility of interpreters. \par The C/C++ programming languages were also very seriously considered, but in the end it was obvious that attempting to deploy a portable and usable framework in a non-interpreted language was something that would not be feasible. Furthermore, the development time-line for this language selection would most likely be much longer. \par Even though the 2.x branch of the framework has been quite successful, the Metasploit staff encountered a number of limitations and annoyances with perl's object-oriented programming model, or lack thereof. The fact that the perl interpreter is part of the default install on many distributions is not something that the Metasploit staff felt was worth detouring the language selection. \section{Design and Architecture} \par The framework was designed to be as modular as possible as to encourage the re-use of code across various projects. The most fundamental piece of the architecture is the \textit{Rex} library which is short for the \texttt{Ruby Extension Library}\footnote{This library has many similarities to the 2.x Pex library}. Some of the components provided by Rex are a wrapper socket subsystem, implementations of protocol clients and servers, a logging subsystem, exploitation utility classes, and a number of other useful classes. Rex itself is designed to have no dependencies other than what comes with the default Ruby install. In the event that a Rex class depends on something that is not included in the default install, the failure to find such a dependency should not lead to the inability to use Rex. \par The framework itself is broken down into a few different pieces, the most low-level being the \textit{framework core}. The framework core is responsible for implementing all of the required interfaces that allow for interacting with exploit modules, sessions, and plugins. This core library is extended by the \textit{framework base} which is designed to provide simpler wrapper routines for dealing with the framework core as well as providing utility classes for dealing with different aspects of the framework, such as serializing module state to different output formats. Finally, the base library is extended by the \textit{framework ui} which implements support for the different types of user interfaces to the framework itself, such as the command console and the web interface. \par Separate from the framework are the modules and plugins that it's designed to support. A framework module is defined as being one of an exploit, payload, encoder, NOP generator, or recon tool. These modules have a well-defined structure and interface for being loaded into the framework. A framework plugin is very loosely defined as something that extends the functionality of the framework or augments an existing feature to make it act in a different manner. Plugins can add new commands to user interfaces, log all network traffic, or perform whatever other action might be useful. \par Figure \ref{fig-arch-pkg} illustrates the framework's inter-package dependencies. The following sections will elaborate on each of the packages described above and the various important subsystems found within each package. Full documentation of the classes and APIs mentioned in this document can be found in the auto-generated API level documentation found on the Metasploit website. \begin{figure}[h] \begin{center} \includegraphics[height=4in,width=4in]{dev_guide_arch_packages} \caption{Framework 3.0 package dependencies} \label{fig-arch-pkg} \end{center} \end{figure} \chapter{Rex} \par The \textit{Rex} library is a collection of classes and modules that may be useful to more than one project. The most useful classes provided by the library are documented in the following subsections. To use the Rex library, a ruby script should require \texttt{rex}. \section{Assembly} \par When writing exploits it is often necessary to have to generate assembly instructions on the fly with variable operands, such as immediate values, registers, and so on. To support this requirement, the Rex library provides classes under the \texttt{Rex::Arch} namespace that implement architecture-dependent opcode generation routines as well as other architecture-specific methods, like integer packing. \subsection{Integer packing} \par Packing an integer depends on the byte-ordering of the target architecture, whether it be big endian or little endian. The \texttt{Rex::Arch.pack\_addr} method supports packing an integer using the supplied architecture type (\texttt{ARCH\_XXX}) as an indication of which byte-ordering to use. \subsection{Stack pointer adjustment} \par Some exploits require that the stack pointer be adjusted prior to the execution of a payload that modifies the stack in order to prevent corruption of the payload itself. To support this, the \texttt{Rex::Arch.adjust\_stack\_pointer} method provides a way to generate the opcodes that lead to adjusting the stack pointer of a given architecture by the supplied adjustment value. The adjustment value can be positive or negative. \subsection{Architecture-specific opcode generation} \par Each architecture that currently has support for dynamically generating instruction opcodes has a class under the \texttt{Rex::Arch} namespace, such as \texttt{Rex::Arch::X86}. The x86 class has support for generating \texttt{jmp}, \texttt{call}, \texttt{push}, \texttt{mov}, \texttt{add}, and \texttt{sub} instructions. \section{Encoding} \par Encoding buffers using algorithms like XOR can sometimes be useful outside the context of an exploit. For that reason, the Rex library provides a basic set of classes that implement different types of XOR encoders, such as variable length key XOR encoders and additive feedback XOR encoders. These classes are used by the framework to implement different types of basic encoders that can be used by encoder modules. The classes for encoding buffers can be found in the \texttt{Rex::Encoding} namespace. \section{Exploitation} \par Often times vulnerabilities will share a common attack vector or will require a specific order of operations in order to achieve the end-goal of code execution. To assist in that matter, the Rex library has a set of classes that implement some of the common necessities that exploits have. \subsection{Egghunter} \par In some cases the exploitation of a vulnerability may be limited by the amount of payload space that exists in the area of the overflow. This can sometimes prevent normal methods of exploitation from being possible due to the inability to fit a standard payload in the amount of room that is available. To solve this problem, an exploit writer can make use of an \textit{egghunting} payload that searches the target process' address space for an egg that is prefixed to a larger payload. This requires that an attacker have the ability to stick the larger payload somewhere else in memory prior to exploitation. In the event that an egghunter is necessary, the \texttt{Rex::Exploitation::Egghunter} class can be used. \subsection{SEH record generation} \par One attack vector that is particularly common on the Windows platform is what is referred to as an SEH overwrite. When this occurs, an SEH registration record is overwritten on the stack with user-controlled data. To leverage this, the handler address of the registration record is point to an address that will either directly or indirectly lead to control of execution flow. To make this work, most attackers will point the handler address at the location of a \texttt{pop/pop/ret} instruction set somewhere in the address space. This action returns four bytes before the location of the handler address on the stack. In most cases, attackers will set two of the four bytes to be equivalent a short jump instruction that hops over the handler address and into the payload controlled by the attacker. \par While the common approach works fine, there is plenty of room for improvement. The \texttt{Rex::Exploitation::Seh} class provides support for generating the normal (static) SEH registration record via the \texttt{generate\_static\_seh\_record} method. However, it also supports the generation of a dynamic registration record that has a random short jump length and random padding between the end of the registration record and the actual payload. This can be used to make the exploit harder to signature in an IDS environment. The generation of a dynamic registration record is provided by \texttt{generate\_dynamic\_seh\_record}. Both methods are by the \texttt{generate\_seh\_record} method that decides which of the two methods to use based on evasion levels. \section{Jobs} \label{rex-jobs} \par In some cases it is helpful to break certain tasks down into the concept of jobs. Jobs are simply defined as finite workitems that have a specific task. Using this definition, the Rex library provides a class named \texttt{Rex::JobContainer} that provides an interface for coordinating various jobs in a centralized manner. New jobs can be added to the job container by calling the \texttt{add\_job} method. Once added, a job can be started by issuing a call to the \texttt{start\_job} method. At any time, a job can be stopped by calling the \texttt{stop\_job} which will also remove the job by calling the \texttt{remove\_job} method. \par For more information how the usage of these API routines, please refer to the auto-generated documentation on Metasploit website. \section{Logging} \par The Rex library provides support for the basic logging of strings to arbitrary log sinks, such as a flat file or a database. The logging interface is exposed to programmers through a set of globally-defined methods: \texttt{dlog}, \texttt{ilog}, \texttt{wlog}, \texttt{elog}, and \texttt{rlog}. These methods represent debug logging, information logging, warning logging, error logging, and raw logging respectively. Each method can be passed a log message, a log source (the name of the component or package that the message came from), and a log level which is a number between zero and three. Log sources can be registered on the fly by \texttt{register\_log\_source} and their log level can be set by \texttt{set\_log\_level}. \par The log levels are meant to make it easy to hide verbose log messages when they are not necessary. The use of the three log levels is defined below: \subsection{LEV\_0 - Default} This log level is the default log level if none is specified. It should be used when a log message should always be displayed when logging is enabled. Very few log messages should occur at this level aside from necessary information logging and error/warning logging. Debug logging at level zero is not advised. \subsection{LEV\_1 - Extra} This log level should be used when extra information may be needed to understand the cause of an error or warning message or to get debugging information that might give clues as to why something is happening. This log level should be used only when information may be useful to understanding the behavior of something at a basic level. This log level should not be used in an exhaustively verbose fashion. \subsection{LEV\_2 - Verbose} This log level should be used when verbose information may be needed to analyze the behavior of the framework. This should be the default log level for all detailed information not falling into LEV\_0 or LEV\_1. It is recommended that this log level be used by default if you are unsure. \subsection{LEV\_3 - Insanity} This log level should contain very verbose information about the behavior of the framework, such as detailed information about variable states at certain phases including, but not limited to, loop iterations, function calls, and so on. This log level will rarely be displayed, but when it is the information provided should make it easy to analyze any problem. \section{Post-exploitation} \par The rex library provides client-side implementations for some advanced post-exploitation, such as DispatchNinja and Meterpreter. These two post-exploitation client interfaces are designed to be usable outside of the context of an exploit. The \texttt{Rex::Post} namespace provides a set of classes at its root that are meant to act as a generalized interface to remote systems via the post-exploitation clients, if supported. These classes allow programmers to write automated tools that can operate upon remote machines in a platform-independent manner. While it's true that platforms may lack analogous feature sets for some actions, the majority of the common set of actions will have functional equivalents. \section{Protocols} \par Support for some of the more common protocols, such as HTTP and SMB, is included in the rex library to help support the development of protocol-specific exploits and to allow for ease of use in other projects. Each protocol implementation exists under the \texttt{Rex::Proto} namespace. \subsection{DCERC} \par The rex library supports a fairly robust implementation of a subset of the DCERPC feature-set and includes support for doing invasive actions such as multi-context bind and packet fragmentation. The classes that support the DCERPC client interface can be found in the \texttt{Rex::Proto::DCERPC} namespace. \subsection{HTTP} \par Minimal support for an HTTP client and server are provided in the rex library. While similar protocol class implementations are provided both in webrick and in other areas of the ruby default standard library set, it was deemed that the current implementations were not well suited for general purpose use due to the existence of blocking request parsing and other such things. The rex-provided HTTP library also provides classes for parsing HTTP requests and responses. The HTTP protocol classes can be found under the \texttt{Rex::Proto::Http} namespace. \subsection{SMB} \par Robust support for the SMB protocol is provided by the classes in the \texttt{Rex::Proto::SMB} namespace. These classes support connecting to SMB servers and performing logins and other SMB-exposed actions like transacting a named pipe and performing other specific commands. The SMB classes are particularly useful for exploits that require communicating with an SMB server. \section{Services} \par One of the limitations identified in the 2.x branch of the framework was that it was not possible to share listeners on the local machine when attempting to perform two different exploits that both needed to listen on the same port. To solve this problem, the 3.0 version of the framework provides the concept of \textit{services} which are registered listeners that are initialized once and then subsequently shared by future requests to allocate the same service. This makes it possible to do things like have two exploits waiting for an HTTP request on port 80 without having any sort of specific conflicts. This is especially useful because it makes it possible to not have to worry about firewall restrictions on outbound ports that would normally only permit connections to port 80, thus making it possible to try multiple client-side exploits against a host with all the different exploit instances listening on the same port for requests. \par Aside from the sharing of HTTP-like services, the service subsystem also provides a way to relay connections from a local TCP port to an already existing stream. This support is offered through the \texttt{Rex::Services::LocalRelay} class. \section{Sockets} \par One of the most important features of the rex library is the set of classes that wrapper sockets. The socket subsystem provides an interface for creating sockets of a given protocol using what is referred to as a \texttt{Comm} factory class. The purpose of the Comm factory class is to make the underlying transport and classes used to establish the connection for a given socket opaque. This makes it possible for socket connections to be established using the local socket facilities as well as by using some sort of tunneled socket proxying system as is the case with Meterpreter connection pivoting. \par Sockets are created using the socket \texttt{Parameter} class which is initialized either directly or through the use of a hash. The hash initialization of the Parameters class is much the same as perl's socket initialization. The hash attributes supported by the Parameter class are documented in the constructor of the Parameter class. \par There are a few different ways to create sockets. The first way is to simply call \texttt{Rex::Socket.create} with a hash that will be used to create a socket of the appropriate type using the supplied or default Comm factory class. A second approach that can be used is to call the \texttt{Rex::Socket::create\_param} method which takes an initialized Parameter instance as an argument. The remaining approaches involve using protocol-specific factory methods, such as \texttt{create\_tcp}, \texttt{create\_tcp\_server}, and \texttt{create\_udp}. All three of these methods take a hash as a parameter that is translated into a Parameter instance and passed on for actual creation. \par All sockets have five major attributes that are shared in common, though some may not always be initialized. The first attributes provide information about the remote host and port and are exposed through the \texttt{peerhost} and \texttt{peerport} attributes, respectively. The second attributes provide information the local host and port and are exposed through the \texttt{localhost} and \texttt{localport} attributes, respectively. Finally, every socket has a hash of contextual information that was used during it's creation which is exposed through the \texttt{context} attribute. While most exploits will have an empty hash, some exploits may have a hash that contains state information that can be used to track the originator of the socket. The framework makes use of this feature to associate sockets with framework, exploit, and payload instances. \subsection{Comm classes} \par The \texttt{Comm} interface used in the library has one simple method called \texttt{create} which takes a \texttt{Parameter} instance. The purpose of this factory approach is to provide a location and transport independent way of creating compatible socket object instances using a generalized factory method. For connections being established directly from the local box, the \texttt{Rex::Socket::Comm::Local} class is used. For connections be established through another machine, a medium specific Comm factory is used, such as the Meterpreter Comm class. \par The \texttt{Comm} interface also supports registered event notification handlers for when certain things occur, like prior to and after the creation of a new socket. This can be used by external projects to augment the feature set of a socket or to change its default behavior. \subsection{TCP sockets} \par TCP sockets in the Rex library are implemented as a mixin, \texttt{Rex::Socket::Tcp}, that extends the built-in ruby Socket base class when the local Comm factory is used. This mixin also includes the \texttt{Rex::IO::Stream} and \texttt{Rex::Socket} mixins. For TCP servers, the \texttt{Rex::Socket::TcpServer} class should be used. \subsection{SSL sockets} \par SSL sockets are implemented on top of the normal Rex TCP socket mixin and makes use of the OpenSSL Ruby support. The module used for SSL TCP sockets is \texttt{Rex::Socket::SslTcp}. \subsection{Switch board routing table} \par One of the advancements in the 3.0 version of the framework is the concept of a local routing table that controls which Comm factory is used for a particular route. The reason this is useful is for scenarios where a box is compromised that straddles an internal network that can't be directly reached. By adjusting the switch board routing table to point the local subnet through a Meterpreter Comm running the host that straddles the network, it is possible to force the socket library to automatically use the Meterpreter Comm factory when anything tries to communicate with hosts on the local subnet. This support is implemented through the \texttt{Rex::Socket::SwitchBoard} class. \subsection{Subnet walking} \par The \texttt{Rex::Socket::SubnetWalker} class provides a way of enumerating all the IP addresses in a subnet as described by a subnet address and a netmask. \section{Synchronization} \par Due to the use of multi-threading, the Rex library provides extra classes that don't exist by default in the Ruby standard library. These classes provide extra synchronization primitives. \subsection{Notification events} \par While Ruby does have the concept of \texttt{ConditionVariable}'s, it lacks the complete concept of notification events. Notification events are used extensively on platforms like Windows. These events can be waited on and signaled, either permanently or temporarily. Please refer to Microsoft's online documentation for more information. This support is provided by the \texttt{Rex::Sync::Event} class. \subsection{Reader/Writer locks} \par A common threading primitive is the reader/writer lock. Reader/writer locks are used to make it possible for multiple threads to be reading a resource concurrently while only permitting exclusive access to one thread when write operations are necessary. This primitive is especially useful for resources that are not updated very often as it can drastically reduce lock contentions. While it may be overkill to have such a synchronization primitive in the library, it's still cool. \par The reader/writer lock implementation is provided by the \texttt{Rex::ReadWriteLock} class. To lock the resource for read, the \texttt{lock\_read} method can be used. To lock the resource for write access, the \texttt{lock\_write} method can be used. \subsection{Reference counting} \par In some cases it is necessary to reference count an instance in a synchronized fashion so that it is not cleaned up or destroyed until the last reference is gone. For this purpose, the \texttt{Rex::Ref} class can be used with the \texttt{refinit} method for initializing references to 1 and the \texttt{ref} and \texttt{deref} methods that do what their names imply. When the reference count drops to zero, the \texttt{cleanup} method is called on the object instance to give it a chance to restore things back to normal. \subsection{Thread-safe operations} \par Some of the built-in functions in Ruby are not thread safe in that they can block other ruby threads from being scheduled in certain conditions. To solve this problem, the functions that have issues have been wrappered with implementations that ensure that not all ruby threads will block. The specific methods that required change were \texttt{select} and \texttt{sleep}. \section{Ui} \par The Rex library provides a set of helper classes that may be useful to certain user interface mediums. These classes are not included by default when requiring \texttt{rex}, so a programmer must be sure to require \texttt{rex/ui} to get the classes described in this section. At the time of this writing, the only user interface medium that has any concrete classes defined is the text, which is synonymous with the console, user interface medium. \subsection{Text} \par The text user interface medium provides classes that allow a programmer to interact with a terminal's input and output handles. It also provides classes for simulating a pseudo-command shell in as robust as manner as possible. \subsubsection{Input} \par The \texttt{Rex::Ui::Text::Input} class acts as a base class for more specific user input mediums. The base class interface provides a basic set of methods for reading input from the user (\texttt{gets}), checking if standard input has closed (\texttt{eof?}), and others. There are currently two classes that extend the base class. The first is \texttt{Rex::Ui::Text::Input::Stdio}. This class simply makes use of the \texttt{\$stdin} globally scoped variable in Ruby. This is the most basic form of acquiring user input. The second class is \texttt{Rex::Ui::Text::Input::Readline} which interacts with the user through the readline library. If no readline installation is present, the class will not be usable. These two classes can be used by the shell classes described later in this subsection. \subsubsection{Output} The \texttt{Rex::Ui::Text::Output} class implements the more generalized \texttt{Rex::Ui::Output} abstract interface. The purpose of the class is to define a set of functions that can be used to provide the user with output. There are currently two classes that implement the textual output interface. The first is \texttt{Rex::Ui::Text::Output::Buffer}. This output medium serializes printed text to a buffer that can be retrieved via the instance's \texttt{buf} attribute. The second class is \texttt{Rex::Ui::Text::Output::Stdio}. This class is the complement to the stdio input class and simply uses the \texttt{\$stdout} global variable to supply the user's terminal with output. \subsubsection{Shell} \par The \texttt{Rex::Ui::Text::Shell} class provides a simple pseudo-shell base class that can be used to implement an interactive prompting shell with a user. The class is instantiated by passing a prompt string and a prompt character (which defaults to \verb#>#) to the constructor. By default, the shell's input and output class instances are initialized to instances of the \texttt{Rex::Ui::Text::Input::Stdio} and \texttt{Rex::Ui::Text::Output::Stdio}, respectively. To change the input and output class instances, a call can be made to the \texttt{init\_ui} method. \par To use the shell, a call must be made to the shell instance's \texttt{run} method. This method accepts either a block context, which will be passed line-based input strings, or will operate in a callback mode where a call is made to the \texttt{run\_single} method on the shell instance. If the second method is used, the class is intended to be overridden with a custom implementation of the \texttt{run\_single} method. \subsubsection{Dispatcher Shell} \par The \texttt{Rex::Ui::Text::DispatcherShell} class extends the \texttt{Rex::Ui::Text::Shell} class by introducing the concept of a generalized command dispatcher interface. The dispatcher shell works by overriding the \texttt{run\_single} method. Unlike the base shell class, the dispatcher shell provides a mechanism by which command dispatchers can be registered for processing input text in a normalized fashion. All command dispatchers should include the \texttt{Rex::Ui::Text::DispatcherShell::CommandDispatcher} mixin which provides a set of helper methods, mainly dealing without wrappering the output of text. \par The registration of a command dispatcher is accomplished by calling either \texttt{enstack\_dispatcher} or \texttt{append\_dispatcher}. The \texttt{enstack\_dispatcher} front inserts the supplied command dispatcher instance so that it will have the first opportunity to process commands. The \texttt{append\_dispatcher} method inserts the supplied command dispatcher instance at the end of the list. To remove command dispatchers, the complementary methods \texttt{destack\_dispatcher} and \texttt{remove\_dispatcher} can be used. \par When a line of input arrives, the base shell class calls the overridden \texttt{run\_single} method which breaks the input string down into an array of arguments as delimited by normal shell characters. The first argument in the string is then evaluated in relation to all of the registered command dispatchers by checking to see if any of them implement a method called \texttt{cmd\_}. If they do, the dispatcher shell calls the method and passes it the parsed argument array. \par In order to make it possible to automatically generate a help menu for all registered command dispatchers, each command dispatcher should implement a method named \texttt{commands} which should return a hash that associates commands with a description of the operation they perform. \subsubsection{Table} \par The \texttt{Rex::Ui::Text::Table} class can be used to format data in the form of a table with a header, columns, and rows. For more information on using the table class, please refer to the auto-generated API documentation on the Metasploit website. \subsubsection{Subscribers} \par The Rex library supports creating classes that are designed to subscribe input and output interfaces via the \texttt{Rex::Ui::Subscriber} interface. This mixin provides a method called \texttt{init\_ui} which can be passed an input and output class instance. These instances should implement the \texttt{Rex::Ui::Text::Input} and \texttt{Rex::Ui::Output} interfaces, respectively. Once \texttt{init\_ui} has been called, subsequent calls to methods like \texttt{print\_line} will be passed down into the initialized output class instance. If no class instance has been defined, the call will be ignored. This makes it possible to provide a way by which classes can interact with the user interface only when desired. To disable user interface interaction, a call can be made to \texttt{reset\_ui} which will disable future input and output classes for the class. \chapter{Framework Core} \par The framework core implements the set of classes that provide an interface to framework modules and plugins. The core portion of the framework is designed by used in an instance-based approach. This means that the entire framework state can be contained within one class instance thereby allowing programmers to have multiple concurrent and separate framework instances in use at the same time rather than forcing everything to share one singleton instance. \par The current major version of the framework core can be accessed through \texttt{Msf::Framework::Major} and the minor version can be accessed through \texttt{Msf::Framework::Minor}. A combined version of these two version numbers can be accessed through \texttt{Msf::Framework::Version} or \texttt{framework.version} on an instance level. The current revision of the framework core interface can be accessed through \\\texttt{Msf::Framework::Revision}. \par The framework core is accessed through an instance of the \texttt{Msf::Framework} class. Creating an instance of the framework is illustrated in figure \ref{fig-code-framework-create}. \begin{figure}[h] \begin{verbatim} framework = Msf::Framework.new \end{verbatim} \caption{Creating an instance of the framework} \label{fig-code-framework-create} \end{figure} \par The framework instance itself is nothing more than a way of connecting the different critical subsystems of the framework core, such as module management, session management, event dispatching, and so on. The manner of using these subsystems will be described in the following subsections. To use the framework core library, a ruby script should require \texttt{msf/core}. \section{DataStore} \par Each framework instance has an instance of the \texttt{Msf::DataStore} class that can be accessed via \texttt{framework.datastore}. The purpose of the datastore in the 3.0 version of the framework is to act as a replacement for the concept of the environment in the 2.x branch. The datastore is simply a hash of values that may be used either by modules or by the framework itself to reference programmer or user controlled values. Interacting with the datastore is illustrated in figure \ref{fig-code-framework-datastore}. \begin{figure}[h] \begin{verbatim} framework.datastore['foo'] = 'bar' if (framework.datastore['foo'] == 'bar') puts "'foo' is 'bar'" end \end{verbatim} \caption{Creating an instance of the framework} \label{fig-code-framework-datastore} \end{figure} \par Modules will inherit values from the framework's global datastore if they are not found in the module's localized datastore. This aspect will be discussed in more detail in chapter \ref{framework-modules}. \section{Event Notifications} \par One of the major goals with the 3.0 version of the framework was to provide developers with a useful event notification system that would allow them to perform arbitrary actions when certain framework events occurred. To support this, each framework instance can have event handlers registered through the \texttt{framework.events} attribute which is an instance of the \texttt{Msf::EventDispatcher} class. \par The \texttt{EventDispatcher} class supports registering events for a few basic different categories. These categories will be discussed individually. One of the nice aspects of the event-driven framework is that modules can automatically indicate their interest in being registered for event handler notifications by simply implementing the event subscriber mixins subscribed below. When a module is loaded into the framework, it will automatically detect that it includes one or more of the subscriber interfaces and automatically register the module with the appropriate event notifiers. This makes it possible for modules to take certain actions when specific events occur. \subsection{Exploit events} \par Event subscribers can be registered to be notified when events regarding exploitation occur. To register an exploit event subscriber, a call should be made to \texttt{framework.events.register\_exploit\_subscriber}. This method should be passed an instance of an object that includes the \texttt{Msf::ExploitEvent} mixin. The type of event that this subscriber will be notified of is when an exploit succeeds. In the event that an exploit succeeds, the subscriber's \texttt{on\_exploit\_success} method will be called with the exploit instance that succeeded and the session instance that it created. \par To remove an event subscriber, a call should be made to\\ \texttt{framework.events.remove\_exploit\_subscriber} passing the object instance that was used to add the subscriber in the first place. \subsection{General framework events} \par To receive event notifications about internal framework events, a general event subscriber can be registered through the \texttt{framework.events.register\_general\_subscriber} method. This method takes an instance of an object that includes the \texttt{Msf::GeneralEventSubscriber} mixin. When a module is loaded into the framework instance, the \texttt{on\_module\_load\_proc} will be called if it is non-nil and will be passed the reference name and class associated with the newly loaded module. When a module instance is created, the \texttt{on\_module\_created\_proc} will be called if it's non-nil and will be passed the newly created module instance. \par To remove an event subscriber, a call should be made to\\ \texttt{framework.events.remove\_general\_subscriber} passing the object instance that was used to add the subscriber in the first place. \subsection{Recon events} \par To receive notifications about reconnaissance events, such as when a new host or service is detected, a recon event subscriber can be registered through the \texttt{framework.events.add\_recon\_subscriber} method. This method takes an instance of an object that implements one or both of the \texttt{Msf::ReconEvent::HostSubscriber} or \texttt{Msf::ReconEvent::ServiceSubscriber} mixins. When a new host is detected or an attribute of a host has changed, a call will be made to the event subscriber's \texttt{on\_host\_changed} method assuming it implements the \texttt{Msf::ReconEvent::HostSubscriber} mixin. When a new service is detected or an attribute of a service has changed, a call will be made to the event subscriber's \texttt{on\_service\_changed} method assuming it implements the \texttt{Msf::ReconEvent::ServiceSubscriber} mixin. \par To remove an event subscriber, a call should be made to\\ \texttt{framework.events.remove\_recon\_subscriber} passing the object instance that was used to add the subscriber in the first place. \subsection{Session events} \par To receive notifications about events pertaining to sessions, a session event subscriber can be registered through the \texttt{framework.events.add\_session\_subscriber} method. This method takes an instance of an object that implements the \texttt{Msf::SessionEvent} mixin. When a new session is opened, the framework will call into the subscriber's \texttt{on\_session\_open} method with the session instance that has just been opened as the first argument. When a session terminates, the framework will call into the subscriber's \texttt{on\_session\_close} method with the session instance that is being closed. \par To remove an event subscriber, a call should be made to\\ \texttt{framework.events.remove\_session\_subscriber} passing the object instance that was used to add the subscriber in the first place. \section{Framework Managers} \par The framework core itself is composed of a few different managers that are responsible for some of the basic aspects of the framework, such as module and plugin management. These managers will be described individually. \subsection{Module management} \par The module management aspect of the framework is one of its most integral parts. The \texttt{Msf::ModuleManager} class is responsible for providing the interface for loading modules and for acting as a factory for module instance creation. The module manager itself can be accessed through the \texttt{framework.modules} attribute. The loading of modules is accomplished by adding a search path to the module manager by making a call to the \texttt{add\_module\_path} method. This method will automatically load all of the modules found within the supplied directory\footnote{The module path must conform to the standard module directory layout, with the base directory structure appearing similar to the \texttt{modules} sub-directory in the framework distribution}. \par Modules are symbolically identified by what is referred to as a \textit{reference name}. The reference name takes a form that is similar to a directory path and is partially controlled by the filesystem path that the module is loaded from. An example of a reference name would be an exploit labeled \texttt{windows/ftp/wsftpd}. This would mean that the exploit was loaded from \texttt{exploits/windows/ftp/wsftpd.rb}. It is important to note that module's must retain a namespace hierarchy that mirrors the path in which they are located. For instance, the example described previously would have the class declared as \texttt{Msf::Exploits::Windows::Ftp::Wsftpd}. This is necessary so that the framework's module manager knows what namespace to look in to see what class was added after loading the file. The reference name of a module can be accessed through the \texttt{refname} attribute on both the class of the module and its instances. \par In order to help solve the potential for module name ambiguities across module types, modules can also be referenced by what is called a \textit{full reference name}. This name is the same as the reference name of the module but is prefixed with the module's type. For instance, the exploit \texttt{windows/ftp/wsftpd} would become \texttt{exploit/windows/ftp/wsftpd}. The full reference named can be accessed through the \texttt{fullname} attribute on both the class of the module and its instances. \par In order to make the module manager easy to use, each different module type is broken down into a more basic class called a module set which is implemented by the \texttt{Msf::ModuleSet} class. The purpose of a module set is to act as a localized factory for each different module type (exploit, encoder, nop, etc). Each module type-specific module set can be accessed through either \texttt{framework.type} or \texttt{framework.modules.type}. For example, if one wanted to enumerate exploit modules, they would use the \texttt{framework.exploits} method to get access to the exploit module set. \par Module sets are implemented in the form of a hash that associates the reference names of modules with their underlying classes. To create an instance of a module, a call is made to the module set's \texttt{create} method passing the reference name of the module that should be instantiated. For example, to create an instance of an exploit named \texttt{windows/ftp/wsftpd}, a call would be made as shown in figure \ref{fig-code-framework-modcreate} \begin{figure}[h] \begin{verbatim} framework.exploits.create('windows/ftp/wsftpd') \end{verbatim} \caption{Creating an instance of a framework module} \label{fig-code-framework-modcreate} \end{figure} \par The table shown in figure \ref{fig-table-modulsets} shows the relation between module types and framework module set accessors. \begin{figure}[h] \begin{center} \begin{tabular}{|l|l|} \hline \textbf{Module Type} & \textbf{Accessor} \\ \hline MODULE\_ENCODER & framework.encoders \\ MODULE\_EXPLOIT & framework.exploits \\ MODULE\_NOP & framework.nops \\ MODULE\_RECON & framework.recon \\ MODULE\_PAYLOAD & framework.payloads \\ \hline \end{tabular} \caption{Module types and their framework accessors} \label{fig-table-modulsets} \end{center} \end{figure} \par To reload the contents of a module, a call can be issued to \texttt{reload\_module} passing the module instance that should be reloaded. This will lead to the framework re-reading the contents of the module's underlying file path and automatically creating a new instance of the module. \subsection{Plugin management} \par One of the new features in the 3.0 version of the framework is the concept of framework plugins. Unlike modules, framework plugins are meant to add features to the framework or to change the behavior of existing aspects of the framework. Plugins have a very loose definition in terms of the scope in which they can operate. For instance, a plugin could add an entirely new module type for use by the framework. Alternatively, a plugin could add commands to the existing user interfaces that interact with the framework. A plugin could also register custom event subscribers for doing things like automatically causing Meterpreter to list the contents of a computer's C drive when a new Meterpreter session is created. The possibilities, as they say, are endless. \par The plugin manager can be accessed through the \texttt{framework.plugins} accessor which is an instance of the \texttt{Msf::PluginManager} class. To load a plugin, a call can be made to \texttt{framework.plugins.load} with the path of the plugin that is to be loaded. Optionally, a second parameter can be passed to the \texttt{load} method that is a hash of option parameters that may be useful to the plugin, such as \texttt{LocalInput} and \texttt{LocalOutput} handles for use with printing strings to the screen or whatever medium is currently being used. The table shown in figure \ref{fig-table-plugin-hash} shows the pre-defined hash elements that can be passed in the option hash. \begin{figure}[h] \begin{center} \begin{tabular}{|l|p{3.5in}|} \hline \textbf{Hash Element} & \textbf{Description} \\ \hline LocalInput & The local input class instance which implements the \texttt{Rex::Ui::Text::Input} interface. \\ \hline LocalOutput & The local input class instance which implements the \texttt{Rex::Ui::Output} interface. \\ \hline ConsoleDriver & The console driver instance of \texttt{Msf::Ui::Console::Driver}. \\ \hline WebDriver & The console driver instance of \texttt{Msf::Ui::Web::Driver}. \\ \hline \end{tabular} \caption{Plugin optional constructor hash elements} \label{fig-table-plugin-hash} \end{center} \end{figure} \par All plugins are reference counted. This is to make it possible to implement singleton plugins that could possibly be loaded more than once but will only have one underlying instance. The reference count to an instance of a plugin is automatically incremented each time \texttt{load} is called on it. \par To unload a framework plugin, a call can be made to \texttt{framework.plugins.unload} passing the instance of the plugin previously loaded as the first parameter. Since all plugins are reference counted, a plugin will not actually be unloaded until its reference count drops to zero. \par For more detail on the implementation of framework plugins, please see chapter \ref{framework-plugins}. \subsection{Recon management} \par The reconnaissance manager is used to provide an interface for reporting information about hosts, services, and other reconnaissance entities. These reports are tracked internally by the recon manager which is implemented by the \texttt{Msf::ReconManager} class. The recon manager can be accessed through the \texttt{framework.reconmgr} accessor. \par This area of the framework is currently undergoing design review and therefore does not have any documentation at this time. \subsection{Session management} \par The session manager is used to track sessions created from within a framework instance as the result of an exploit succeeding. The purpose of sessions is to expose features to a programmer that allow it to be interacted with. For instance, a command shell session allows programmers to send commands and read responses to those commands through a well-defined API. For more information on sessions and how they can be interacted with, please see chapter \ref{framework-sessions}. The session manager itself can be accessed through the \texttt{framework.sessions} accessor and is an instance of the \texttt{Msf::SessionManager} class. \par The primary purpose of the session manager is to provide an interface for registering new sessions and assigning them a unique session identifier as well as allowing sessions to be deregistered when they are destroyed. The registering of sessions with the framework session manager is accomplished by making a call into the \texttt{framework.sessions.register} method which takes an instance of a session as its argument. This method will assign the session a unique session identifier and add it to the managed hash of sessions. Sessions can be enumerated by making a call into \texttt{framework.sessions.each\_sorted} or by calling any of the hash-compatible enumeration methods. To obtain the session instance associated with a particular session identifier, the \texttt{framework.sessions.get} method can be called with the session identifier to look up. When a session is being destroyed, a call must be made to \texttt{framework.sessions.deregister} passing the instance of the session being destroyed as the first argument. \subsection{Job management} \par Each framework instance supports running various tasks in the context of worker threads through the concept of jobs. The job interface can be accessed through the \texttt{framework.jobs} accessor which is an instance of the \texttt{Rex::JobContainer} class. For more information on jobs, please refer to the job explanation in the Rex documentation in section \ref{rex-jobs}. \section{Utility Classes} \par Some classes in the framework core are intended to be used to make certain tasks simpler without being out of scope of the core aspects of the framework. These classes are described below. \subsection{Exploit driver} \par The \texttt{Msf::ExploitDriver} class encapsulates the task of running an exploit module in terms of coordinating the validation of required module options, the validation of target selection, the generation of a selected payload, and the execution of exploit and payload setup and cleanup. These operations are what has to be performed when attempting to execute an exploit. \par An instance of an exploit driver is initialized as described in figure \ref{fig-code-exploit-driver}. \begin{figure}[h] \begin{verbatim} driver = Msf::ExploitDriver.new(framework) driver.payload = payload_instance driver.exploit = exploit_instance driver.target_idx = 0 session = driver.run \end{verbatim} \caption{Using the ExploitDriver class} \label{fig-code-exploit-driver} \end{figure} \par When the \texttt{run} method is called, the first step is to validate the options required by the payload and the exploit that have been selected. This is done by calling the public \texttt{validate} method on the exploit driver instance. In the event that options fail to validate or that a target index has not been properly selected, an exception will be thrown to the caller. After validation has completed, the exploit's \texttt{TARGET} data store element is set to the selected target index. From there, an encoded version of the payload is generated by calling \texttt{generate\_payload} on the exploit instance. Once completed, the exploit is set up by calling \texttt{setup} on the exploit module instance and finally the actual exploit code is triggered by calling \texttt{exploit} on the exploit module instance. \par Once exploitation has completed, the exploit driver calls the \texttt{stop\_handler} method on the payload module instance and then calls the \texttt{cleanup} method on the exploit module instance. \par The exploit driver can also be instructed to run the exploit in the context of a job. When this is done, the underlying exploitation operation is done in the context of a job worker thread by calling \texttt{framework.jobs.start\_bj\_job}. The exploit driver can be told to use a job by setting the \texttt{use\_job} attribute to true. \subsection{Encoded payload} \par The purpose of the \texttt{Msf::EncodedPayload} class is to encapsulate the operation of encoding a payload with an arbitrary set of requirements. To generate an encoded payload, an instance of an \texttt{Msf::EncodedPayload} class must be created by passing its constructor an instance of a payload as well as an optional hash of requirements that will be used during the generation phase. This can be accomplished by calling the class' \texttt{create} method as shown in figure \ref{fig-code-enc-payload}. \begin{figure}[h] \begin{verbatim} encoded = Msf::EncodedPayload.create(payload_instance, 'BadChars' => "\x0a\0xd", 'Space' => 400, 'Prepend' => "\x41\x41", 'Append' => "\xcc\xcc\", 'SaveRegisters' => "edi", 'MinNops' => 16) \end{verbatim} \caption{Creating an instance of an EncodedPayload} \label{fig-code-exploit-driver} \end{figure} \par Once an encoded payload instance has been created, the next step is to make a call to the instance's \texttt{generate} method which will return the encoded version of the payload. After generation has occurred, the following attributes can be accessed on the encoded payload instance in order to get information about the now-encoded payload. Figure \ref{fig-table-enc-payload} shows the attributes and their purposes. \begin{figure}[h] \begin{center} \begin{tabular}{|l|p{3.5in}|} \hline \textbf{Attribute} & \textbf{Description} \\ \hline raw & The un-encoded raw payload buffer. \\ \hline encoded & The encoded payload buffer which may be equal to raw if no encoder was used. \\ \hline nop\_sled\_size & The size of the NOP sled prepended to the encoded payload. Zero if no NOPs were generated. \\ \hline nop\_sled & The NOP sled portion of the encoded payload, if any. \\ \hline encoder & The encoder module instance that was used to encode the payload. \\ \hline nop & The nop module instance that was used to generate the NOP sled, if any. \\ \hline \end{tabular} \caption{\texttt{Msf::EncodedPayload} instance attributes} \label{fig-table-enc-payload} \end{center} \end{figure} \par To control the behavior of the encoded payload class, an optional hash can be passed into the constructor. The table in figure \ref{fig-table-enc-payload-options} describes the options that can be specified and the affect they have on behavior. \begin{figure}[h] \begin{center} \begin{tabular}{|l|p{3.5in}|} \hline \textbf{Hash Element} & \textbf{Description} \\ \hline BadChars & A string of bad characters to avoid when encoding. \\ \hline Encoder & The name of the preferred encoder to use. \\ \hline MinNops & The minimum number of NOPs to generate. \\ \hline MaxNops & The maximum number of NOPs to generate. \\ \hline Space & The amount of room left for use by the payload. If this value is not specified, then NOP padding will not be performed and there will be no restrictions on payload size. \\ \hline SaveRegisters & A white-space separated list of registers to save when generating the NOP sled. \\ \hline Prepend & Raw instructions or text to prepend to the encoded payload. \\ \hline Append & Raw instructions or text to append to the encoded payload. \\ \hline \end{tabular} \caption{\texttt{Msf::EncodedPayload} constructor options} \label{fig-table-enc-payload-options} \end{center} \end{figure} \chapter{Framework Base} \par The framework base is a library layer built on top of the framework core that adds classes that make dealing with the framework easier. It also provides a set of classes that could be useful to third party development tools that don't necessarily fit within the scope of the framework core itself. The classes that compose the framework base are described in the following subsections. To use the framework base library, a ruby script should require \texttt{msf/base}. \section{Configuration} \par One important aspect of a managed framework installation is the concept of persistent configuration and methods for getting information about the structure of an installation, such as the root directory of the installation and other types of attributes. To facilitate this, the framework base library provides the \texttt{Msf::Config} class that has methods for obtaining various installation directories. It also supports the serialization of configuration files. The table shown in figure \ref{fig-table-config} describes the different methods that can be used to obtain configuration information. \begin{figure}[h] \begin{center} \begin{tabular}{|l|p{3.5in}|} \hline \textbf{Method} & \textbf{Description} \\ \hline install\_root & The installation's root directory. \\ \hline config\_directory & The configuration directory (\verb#~/.msf3#). \\ \hline module\_directory & install\_root + '/modules'. \\ \hline plugin\_directory & install\_root + '/plugins'. \\ \hline log\_directory & config\_directory + '/logs'. \\ \hline session\_log\_directory & config\_directory + '/logs/sessions'. \\ \hline user\_module\_directory & config\_directory + '/modules'. \\ \hline data\_directory & install\_root + '/data'. \\ \hline config\_file & config\_directory + '/config'. \\ \hline load & Loads the contents of a configuration file and returns an instance of a \texttt{Rex::Parser::Ini} object. \\ \hline save & Saves the supplied option hash to the configuration file supplied as \texttt{'ConfigFile'} in the options hash or the config\_file by default. \\ \hline \end{tabular} \caption{\texttt{Msf::Config} accessor methods} \label{fig-table-config} \end{center} \end{figure} \section{Logging} \par The framework base library provides a wrapper class that can be used to control debug logging at an administrative level by providing methods for enabling log sources and for controlling logs that are applied to sessions created from within a framework instance. To initialize logging, a call must be made to \texttt{Msf::Logging.init} which will register the log sources \texttt{rex}, \texttt{core}, and \texttt{base} as being directory at \texttt{framework.log} as found in the \texttt{Msf::Config.log\_directory}. Individual log sources can be subsequently enabled or disabled by making calls to \texttt{Msf::Logging.enable\_log\_source} and \texttt{Msf::Logging.disable\_log\_source}, respectively. When session logging is enabled, calls can be issued to \texttt{start\_session\_log} and \texttt{stop\_session\_log} which operate on a provided session to start or stop logging to a session-specific log file in the \texttt{Msf::Config.session\_log\_directory} directory. \section{Serialization} \par To make life easier for framework programmer's, the framework base library provides a class that can be used to serialize information about modules, such as their description, options, and other information to a uniform, human readable format. The class that provides this feature is the \texttt{Msf::Serializer::ReadableText} class. For more information, please review the auto-generated API documentation on the Metasploit website. \section{Sessions} \par While the framework core has an abstract concept of sessions as described through the \texttt{Msf::Session} base module, the framework base actually provides some of the concrete implementations. This separation was done to eliminate module-specific session implementations from the framework core as the core should have no conceptual dependencies on modules that use it where as the base library is more of a facilitation layer for subscribers of the framework. The two sessions currently implemented in the base library are the \texttt{CommandShell} session and the \texttt{Meterpreter} session. \subsection{CommandShell} \par The command shell session implements the framework core \\ \texttt{Msf::Session::Provider::SingleCommandShell} interface against a connected stream, such as a TCP connection. For more information about this mixin, please read chapter \ref{framework-sessions}. \subsection{Meterpreter} \par The meterpreter session implements the \texttt{Msf::Session::Interactive} and \\ \texttt{Msf::Session::Comm} mixins. This allows it to be operated through an interactive user shell and also indicates to the framework that internet traffic can be routed (pivoted) through the session by making use of it as a Comm socket factory. The session itself is merely an extension of the \texttt{Rex::Post::Meterpreter} class which operates against a connected stream, such as a TCP connection. \section{Simplified Framework} \par The simplified framework provides methods that make the framework and the different module types easier to use by providing wrapper methods that handle most of the actions that would be common to a subscriber of the framework. To create an instance of the simplified framework, the \texttt{Msf::Simple::Framework.create} method should be called along with an optional hash. The return value is an instance of an \texttt{Msf::Framework} class that has been extended by the \texttt{Msf::Simple::Framework} mixin. Existing framework instances can also be simplified by calling the \texttt{Msf::Simple::Framework.simplify} method with the existing framework instance as the first argument. \par The creation of a simplified framework instance automatically leads to the initialization of the \texttt{Msf::Config} class and the \texttt{Msf::Logging} class. Any existing configuration file is also automatically loaded. The default global module directory (\texttt{Msf::Config::module\_directory}) and the user-specific module directory (\texttt{Msf::Config::user\_module\_directory}) are added as search paths to the framework instance which leads to the loading of all modules within the two directories. Finally, a general event subscriber is registered with the framework instance that will be called whenever module instances are created within the framework. This allows the simplified framework the opportunity to simplify each created module instance. \par Each module type has a simplified framework module mixin that is automatically used to extend created module instances via the general event subscriber described above. For example, when an exploit module instance is created, the instance is extended by the \texttt{Msf::Simple::Exploit} mixin. Each different module mixin provides a helper method or methods for driver that specific module type's primary action or actions. Furthermore, each module instance has methods that can be used to save and restore module-specific configuration elements through the \texttt{save\_config} and \texttt{load\_config} methods. Each module-specific mixin is described individually below. \subsection{Exploit} \par The simplified exploit mixin provided in \texttt{Msf::Simple::Exploit} extends each exploit module instance with a method called \texttt{exploit\_simple}. This method takes a hash parameter that is used to control the exploitation of something by creating an instance of an \texttt{Msf::ExploitDriver} class and doing all the required initialization and configuration of the module prior to issuing the call to the exploit driver's \texttt{run} method. If the operation succeeds, the return value is a session instance. Otherwise, an exception will be thrown. For more information about the hash elements that can be passed in, please refer to the auto-generated API documentation on the Metasploit website. \subsection{NOP} \par The simplified NOP mixin provided in \texttt{Msf::Simple::Nop} extends each nop module instance with a method called \texttt{generate\_simple}. This method takes the length of the sled generate and the hash of options that should be used for the generation. On success, the return value is a buffer that is encoded using the \texttt{Msf::Simple::Buffer} class using the format specified in the option hash as the \texttt{'Format'} element. If no format is specified, the raw version of the NOP sled is returned. \subsection{Payload} \par The simplified payload mixin provided in \texttt{Msf::Simple::Payload} extends each payload module instance with a method called \texttt{generate\_simple}. This method takes a hash of options that are used to generate a payload buffer. The elements that can be used in the option hash can be found in the auto-generated API documentation found on the Metasploit website. If the operation is successful, the encoded payload buffer will be serialized to the format supplied in the \texttt{'Format'} hash element. If the format is not raw, any staged payloads will also be appended to the serialized buffer. \subsection{Recon} \par The reconnaissance interface is under design review. \chapter{Framework Ui} \par The framework user interface library is used to encapsulate code common to different user interface mediums to allow third party development and extension of custom user interfaces separate from those distributed with the framework itself. Each different user interface medium is encapsulated in an abstract \textit{driver} class, \texttt{Msf::Ui::Driver} that is designed to have an actual interface that is specific to the underlying user interface medium being used. \par The inherited driver base class simply defines three methods that are to be common to all user interfaces. Those methods are \texttt{run}, \texttt{stop}, and \texttt{cleanup}. Their names imply the actions that are to be performed. Each of the currently defined user interface mediums will be explained individually in the following sections. To use the framework ui library, a ruby script should require \texttt{msf/ui}. \section{Console} TBD. \section{Web} TBD. \chapter{Framework Modules} \label{framework-modules} \par The primary purpose of the Metasploit framework is to facilitate the development of modules that can plug into the framework core and be shared with other existing modules. For instance, an advanced encoder module can be plugged into the framework and will be automatically applied to payloads of a compatible architecture and platform. This makes it so there are zero code change requires due to the fact that all modules conform to a well-defined interface with which they can be interacted with by the framework. As another example, new payloads can be developed and are immediately usable to all exploits without modification. This eliminates the need to copy static payload blobs into exploits as is most common with proof of concept exploits. This chapter is dedicated to describing the interfaces that each module type exposes in order to provide an understanding of what it takes to implement each module type. \par At some level, all modules inherit from the module base class provided in \texttt{Msf::Module}. This class implements all of the things that are common to Metasploit framework objects, such as common accessors. When a module is loaded into the framework, a copy of the class that gets added is made that that is what is used for future instantiations of the module. The copy class then has some attributes set that allow the framework to look at some of the information of the module at a glance without having to create an instance. This information can be accessed through a set of class methods and attributes that are described in figure \ref{fig-table-mod-class-methods}. \begin{figure}[h] \begin{center} \begin{tabular}{|l|p{3.5in}|} \hline \textbf{Method} & \textbf{Description} \\ \hline framework & The framework instance that the module is associated with. \\ \hline type & The module's symbolic type. One of \texttt{MODULE\_ENCODER}, \texttt{MODULE\_EXPLOIT}, \texttt{MODULE\_NOP}, \texttt{MODULE\_PAYLOAD}, or \texttt{MODULE\_RECON} \\ \hline fullname & The complete symbolic name of the module including is string type. For example: exploit/windows/ms03\_026 \\ \hline rank & The module's integer rank to indicates its quality. The rank is used by the framework when selecting which encoders, payloads, and NOP generators to use. \\ \hline rank\_to\_s & Returns the string representation of the module's rank \\ \hline refname & The module's symbolic reference name. For example: windows/ms03\_026 \\ \hline orig\_cls & The original, non-duplicated class that was loaded for the module. \\ \hline file\_path & The file path that the module was loaded from. \\ \hline \end{tabular} \caption{\texttt{Msf::Module} class methods} \label{fig-table-mod-class-methods} \end{center} \end{figure} \par To support generic initialization, each module defines its own custom information hash that is passed to the constructor of \texttt{Msf::Module}. This information class is then assigned to the instance attribute \texttt{module\_info} and then processed. The parts that are common to all modules are broken down and transformed into uniform types that can be accessed through instance methods. The same methods that are accessible through the module class can also be used through the class instance (as shown in figure \ref{fig-table-mod-class-methods}). \par The table in figure \ref{fig-table-mod-info} shows how the common module information hash elements are broken down into their respective data types and the methods that can be used to access them. \begin{figure}[h] \begin{center} \begin{tabular}{|l|l|l|p{2.0in}|} \hline \textbf{Hash Element} & \textbf{Accessor} & \textbf{Type} & \textbf{Description} \\ \hline Name & name & String & The short name of the module. \\ \hline Alias & alias & String & An alias string for the refname of the module. \\ \hline Description & description & String & A longer description of the module. \\ \hline Version & version & String & The current revision of the derived module. \\ \hline Author & author & Array & An array of \texttt{Msf::Author} instances. \\ \hline Arch & arch & Array & An array of architectures (like \texttt{ARCH\_X86}). \\ \hline Platform & platform & PlatformList & An instance of a \texttt{Msf::PlatformList}. \\ \hline References & references & Array & An array of \texttt{Msf::Reference} instances. \\ \hline Options & options & OptionContainer & Options conveyed in the hash are added to the module's option container. \\ \hline AdvancedOptions & options & OptionContainer & Options conveyed in the hash are added to the module's option container as advanced options. \\ \hline DefaultOptions & options & OptionContainer & Previously registered options have their default value modified. \\ \hline Privileged & privileged & Bool & Whether or not the module requires or grants privileged access. \\ \hline Compat & compat & Hash & A hash of compatibility flags. \\ \hline \end{tabular} \caption{\texttt{Msf::Module} information hash accessors} \label{fig-table-mod-info} \end{center} \end{figure} \par Some of the information hash accessors also have helper methods that make it easier to interact with some of them. For instance, the \texttt{Arch} hash element array contained within the \texttt{arch} attribute can be serialized to a comma separated string by calling \texttt{arch\_to\_s}. Architectures can also be enumerated by calling \texttt{each\_arch} and passing it a block that accepts the architecture as a parameter. It is also possible to check if a module supports an architecture by calling the \texttt{arch?} method and passing it the architecture to check for as a parameter. Like architectures, platforms can be serialized to a string by calling \texttt{platform\_to\_s}. \par The \texttt{Author} hash element can also be converted to a comma separated string of authors by calling \texttt{author\_to\_s}. The array of \texttt{Msf::Author} instances contained within the \texttt{author} array attribute can be enumerated by calling \texttt{each\_author} and passing it a block that takes an author instance as its first parameter. \par The \texttt{Msf::Module} class also has some helper methods that allow users to quickly check if a module is of a specific type by calling the \texttt{?} method set. For instance, if a caller wished to see if a module instance was an exploit, they could call \texttt{mod.exploit?}. \par Since the Rex library introduces the concept of socket communication factories (through the \texttt{Comm} class), each module has an attribute that can return the \texttt{Comm} instance that was used or preferred. By default, all modules return \texttt{Rex::Socket::Comm::Local}. \par Each module has its own instance-based datastore which is an instance of the \texttt{Msf::ModuleDataStore} class and can be accessed through the \texttt{datastore} accessor. This mirrors the functionality provided by the global framework datastore in that it provides a localized variable to value association for use in satisfying required options. For instance, if a module requires the \texttt{RHOST} option to be set to a value, the module's data store must have a hash entry for \texttt{RHOST}. Alternatively, modules are designed to be able to fall back on the framework global datastore if their localized datastore does not have a value for a variable being checked for. This provides a basic level of variable/value inheritance. In some cases, modules may wish to share their localized copies of the datastore with other modules without having to taint the global datastore. This can be accomplished by calling the \texttt{share\_datastore} method on a module instance and passing it a data store instance as the first argument. \par Finally, framework module's are designed to be able to indicate their relative compatibilities with other modules. For instance, an exploit may wish to indicate that it is incompatible with a specific class of payload connection mediums. This is accomplished through the \texttt{Compat} information hash element. After the compatibility layer has been initialized, calls can be made to a module's \texttt{compatible?} method by passing another module instance as the argument. If the supplied module instance is compatible with the instance that's being checked against, then true is returned. \par This basic interface provides a generalized view into the behavior and expectations of framework modules. However, all module types have well-defined interfaces for dealing with the actions that they are meant to undertake. These specific interfaces will be described in the following sections. \section{Encoder} \par Encoder modules are used to generate transformed versions of raw payloads in a way that allows them to be restored to their original form at execution time and then subsequently executed. To accomplish this, most encoders will take the raw form of the payload and run it through some kind of encoding algorithm, like bitwise XOR. After the encoded version is generated, a decoding stub is prefixed to the encoded version of the payload. This stub is responsible for performing the inverse operation on the buffer attached to the decoder when it executes. After the decoder restores the payload to its original form, it will transfer execution to the start of the now normalized payload. \par To support the above described encoder model, the Metasploit framework provides the \texttt{Msf::Encoder} class which inherits from the \texttt{Msf::Module} base class. All encoders must inherit from the \texttt{Msf::Encoder} class at some level to ensure that encoder-specific methods are included in the derived class. \par Like the module information hash, encoders have some specialized information hash elements that describe information about the encoder being used. The information that encoder modules need to describe are the attributes of the decoder which is conveyed through the \texttt{Decoder} information hash element. The \texttt{Decoder} hash element references another hash that contains decoder specific properties. These are described in the table shown in figure \ref{fig-table-encoder-hash} along with their types and module instance accessors. \begin{figure}[h] \begin{center} \begin{tabular}{|l|l|l|p{2.0in}|} \hline \textbf{Hash Element} & \textbf{Accessor} & \textbf{Type} & \textbf{Description} \\ \hline Stub & decoder\_stub & String & The raw stub to be prefixed to encoded payloads. \\ \hline KeyOffset & decoder\_key\_offset & Fixnum & The offset to the key in the decoder stub. \\ \hline KeySize & decoder\_key\_size & Fixnum & The size of the decoder key in bytes. \\ \hline BlockSize & decoder\_block\_size & Fixnum & The size of each encoding block in bytes. \\ \hline KeyPack & decoder\_key\_pack & String & The byte-ordering to use when packing the key. The default is 'V'. \\ \hline \end{tabular} \caption{\texttt{Msf::Encoder} \texttt{Decoder} information hash accessors} \label{fig-table-encoder-hash} \end{center} \end{figure} \par Each of the methods described in figure \ref{fig-table-encoder-hash} are designed to be overridable so that derived encoder classes can dynamically choose the values returned by them rather than being forced to initialize them in a static hash element. The decoder hash itself can be accessed through the \texttt{decoder\_hash} method in case an encoder module wishes to convey non-standard information in the hash for later reference. \par Perhaps of more importance that the decoder initialization vector is how the encoding process is exposed. The base class \texttt{Msf::Encoder} implements an instance method named \texttt{encode} which takes a buffer as the first argument, a string of bad characters (or nil) as the second argument, and an optional encoder state as the third argument. The \texttt{encode} method wraps the encoding process in terms of selecting a decoder key, initializing the encoder state, and then performing the actual encoding operation. Once completed, the encoded buffer is returned to the caller. \subsection{encode} \par At a more detailed level, the \texttt{encode} method first creates an instance of a \texttt{Msf::EncoderState} class if one was not supplied as the third argument of \texttt{encode}. The purpose of the encoder state is to contain transient information about a specific encoding in a non-global location. After creating the encoder state instance, \texttt{encode} prepends any encoder-specific to the raw payload that might be necessary through the use of the \texttt{prepend\_buf} instance method on the encoder module. This method is intended to be overridden and used as necessary. By default, an empty string is returned, effectively leaving the buffer in the same state that it was. \par After prepending the raw buffer as necessary, the \texttt{encode} method then selects a decoder key if the \texttt{decoder\_key\_size} method returns a non-zero value and the encoder state currently has a \texttt{nil} key. This is accomplished by calling the \texttt{find\_key} method on the encoder module which has a default implementation that is intended to work across all encoder modules. Once a key has been selected, the \texttt{init\_key} method is called on the encoder state object to set the \texttt{state.key} and \texttt{state.orig\_key} attributes. If no key is found, a \texttt{Msf::NoKeyError} exception is raised. \par The next step is to initialize some of the encoder state specific attributes by calling the \texttt{init\_state} method on the encoder module instance which simply stores the currently defined decoder key offset, size, and pack as attributes of the encoder state as conveyed through the accessor methods on the encoder module instance itself. The encoder state then has the string of bad characters and the raw buffer set as attributes so that they can be contextually referenced throughout the encoding process. \par With the encoder state finally initialized, the next step is to begin the encoding process by calling the \texttt{encode\_begin} method on the encoder module instance. This method simply does nothing in its default implementation, but it is designed to allow derived encoder modules to alter the attributes of the encoder state prior to actually starting the encoding process. Once \texttt{encode\_begin} returns, the \texttt{encode} method makes a call into the \texttt{do\_encode} method by passing it the buffer, bad characters, and initialized encoder state. This is the method that does the actual encoding work and could possibly be overridden if the default implementation was not suitable for a given encoder. \par Once \texttt{do\_encode} completes, the \texttt{encode} method makes a call into \texttt{encode\_end} and passes the encoder state as an argument. The default implementation of this method simply does nothing, but it is provided as a means by which an encoder can hook into the finalization of the encoding process to alter the results that will be returned to the caller. \subsection{do\_encode} \par The \texttt{do\_encode} method is the actual workhorse of the encoding process. It starts by making a copy of the decoder stub by calling the encoder module instance's \texttt{decoder\_stub} method and passing it the encoder state as an argument. The \texttt{decoder\_stub} method is the only one that takes an encoder state as an argument as some encoders may generate dynamic decoder stubs depending on the state. \par After obtaining the decoder stub, the next step is to substitute the packed version of the decoder key at whatever offset was conveyed in the decoder information hash through the \texttt{KeyOffset} and \texttt{KeySize} as well as the \texttt{KeyPack}. These attributes are gotten through the encoder state's attributes since it's possible that a derived encoder may wish to alter their values to be non-static between iterations of the encoding process. \par Finally, the actual block-based encoding occurs by simply walking the raw buffer in block size chunks calling the \texttt{encode\_block} method on each chunk. This method is passed the encoder state and the chunk to be encoded. By default, the \texttt{encode\_block} method simply returns the block it is passed, but all encoders are intended to override this method to return the encoded value of the block based on the current encoder state. \par After all the blocks have been encoded, the encoder state's \texttt{encoded} attribute will contain the encoded version of each blocked. The \texttt{do\_encode} method then prepends the decoder stub to the front of the encoded buffer and then checks to see if the complete stub + encoded buffer has any bad characters. If bad characters are found, a \texttt{Msf::BadcharError} exception is raised to the caller indicating what character and position the bad character was found at in the encoded buffer. If all goes well, the \texttt{do\_encode} method returns true. \subsection{Helper methods} \par Internal the encoder module class are some instance helper methods that can be used by derived classes to make things easier. For instance, the encoder module base class has a method called \texttt{has\_badchars?} that can be used to check to see if the supplied buffer has any of the supplied bad characters. If it does, the index of the first bad character found is returned. Otherwise, \texttt{nil} is returned. \section{Exploit} \par Exploit modules are used to leverage vulnerabilities in a manner that allows the framework to execute arbitrary code. This broad definition encompasses things like command execution and code execution which are described in terms of payloads in the framework nomenclature. Support for exploit modules is provided through the \texttt{Msf::Exploit} base class. All exploit modules must derive from the \texttt{Msf::Exploit} base class at some level. The primary interface exposed by exploit modules to the framework are methods that can be used to check to see if a target is vulnerable and to actually launch the exploit. These methods will be discussed more later in this section. \par Like the module information hash, exploit modules have a few exploit module specific information hash elements that are used to control the way the framework interacts with the exploit module and to control the exploit module itself. These exploit module specific hash elements are described in the table shown in figure \ref{fig-table-exploit-hash}. \begin{figure}[h] \begin{center} \begin{tabular}{|l|l|l|p{2.0in}|} \hline \textbf{Hash Element} & \textbf{Accessor} & \textbf{Type} & \textbf{Description} \\ \hline Stance & stance & Exploit::Stance & One of \texttt{Exploit::Stance::Aggressive} or \texttt{Exploit::Stance::Passive}. \\ \hline Targets & targets & Array & An array of \texttt{Msf::Target} instances. \\ \hline DefaultTarget & default\_target & Fixnum & The default target index to use, if any. \\ \hline Payload & payload\_info & Hash & A hash of elements that controls the exploit's interaction with payloads. \\ \hline \end{tabular} \caption{\texttt{Msf::Exploit} information hash elements} \label{fig-table-exploit-hash} \end{center} \end{figure} \par The following subsections will describe the distinctions between different types and stances of exploit modules as well as the interfaces that can be used to operate upon them. \subsection{Stances} \par In the 3.0 version of the framework, exploit modules are designed to take a stance that describes how they go about exploiting their vulnerability at a very general level. While there is much debate in how this breakdown should occur, the framework puts them into two basic categories called \textit{stances}. The first stance that an exploit can take is an aggressive stance. In this mode, an exploit is actively triggering an exploit. The second stance that an exploit can take is a passive stance. In this mode, an exploit is waiting for something to occur, such as a client connecting to a server, so that the exploit can be triggered. Stances are not designed to take locality into account. They merely break down the manner in which the exploit will operate. \par The framework uses the exploit's stance to figure out whether how it should go about executing the \texttt{exploit} method. For instance, passive exploits are implied to take longer because they are waiting for some event to trigger the exploitation. For that reason, it is better for the framework to run passive exploits in the context of a job rather than blocking on their exploit routine. Furthermore, passive exploits may be capable of exploiting more than one target before they are completed. \par For a module to indicate a passive stance it should initialize the \texttt{Stance} information hash element to \texttt{Msf::Exploit::Stance::Passive}. If a module wishes to take an aggressive stance, which is the default, it should initialize the \texttt{Stance} information hash element to \texttt{Msf::Exploit::Stance::Aggressive}. \subsection{Types} \par To further categorize exploits, each exploit is described in terms of an \textit{exploit type}. The purpose of the exploit type is to indicate the locality of the exploit in terms of whether or not it is exploiting a remote machine, a local application, or is capable of operating as both types. \par The remote exploit type, as indicated by \texttt{Msf::Exploit::Type::Remote}, is used tell the framework that the exploit is designed to operate against a target other than that of the local machine. While this doesn't explicitly limit the exploit to the use of network communication, that is typically what is implied. Exploit modules can indicate that they are a remote exploit module by inheriting from \texttt{Msf::Exploit::Remote} which inherits from \texttt{Msf::Exploit}. \par The local exploit type, as indicated by \texttt{Msf::Exploit::Type::Local}, is used to tell the framework that the exploit is designed to operate against an application or service running on the local machine. This definition typically limits it to exploitation by means other than network communication on the local machine. Exploits modules can indicate that they are a local exploit module by inheriting from \texttt{Msf::Exploit::Local} which inherits from \texttt{Msf::Exploit}. \par The third exploit type, \texttt{Msf::Exploit::Type::Omni}, is used to indicate to the framework that the exploit module is capable of operating both locally and remotely. Exploit modules that fit this criteria should inherit from the \texttt{Msf::Exploit} class directly. \subsection{Interface} \par To interact with exploit modules, the framework uses a well-defined interface that is exposed by the exploit module base class. These methods, along with their purposes, are described in the following subsections. \subsubsection{check} \par The exploit module \texttt{check} method is used to indicate whether or not a remote machine is thought to be vulnerable. The default implementation of the \texttt{check} method simply returns that it is unsupported by the exploit module. However, a complete set of codes can be returned from the \texttt{check} method as shown in the table in figure \ref{fig-table-exploit-checkcodes}. \begin{figure}[h] \begin{center} \begin{tabular}{|l|p{2.5in}|} \hline \textbf{Check Code} & \textbf{Description} \\ \hline Exploit::CheckCode::Safe & The target is not exploitable. \\ Exploit::CheckCode::Detected & The target service is running, but could not be validated. \\ Exploit::CheckCode::Appears & The target appears to be vulnerable. \\ Exploit::CheckCode::Vulnerable & The target is vulnerable. \\ Exploit::CheckCode::Unsupported & The exploit does not support \texttt{check}. \\ \hline \end{tabular} \caption{Codes returned from calls to \texttt{exploit.check}} \label{fig-table-exploit-checkcodes} \end{center} \end{figure} \subsubsection{exploit} \par The exploit module's \texttt{exploit} method is the entry point that is used to kick off the exploitation process. Prior to calling this method, the framework will have ensured that all required options have been set and that a payload has been generated for use by the exploit. After that, it's up to the exploit to perform whatever action is necessary to trigger the vulnerability in question. \subsubsection{setup} \par If a payload instance has been created and assigned to the exploit, the \texttt{setup} method will initialize the payload's handler by calling \texttt{setup\_handler} on it and will start the handler by calling \texttt{start\_handler}. The \texttt{setup} method is called by the framework prior to calling the exploit module's \texttt{exploit} method. \subsubsection{cleanup} \par The \texttt{cleanup} method gives an exploit module the chance to remove any resources that were created during the call to \texttt{exploit} and also gives the exploit module base class a chance to call \texttt{cleanup\_handler} on the payload instance that's associated with the exploit, if there is one. \subsubsection{generate\_payload} \par This method is used by the framework to generate a payload using either a passed payload instance as the argument or by using the \texttt{payload\_instance} attribute of the exploit module instance. The return value is an instance of an \texttt{EncodedPayload} that takes into account some of the limiting payload factors described in the exploit module's \texttt{payload\_info} hash. It also takes into account any target-specific limiting payload factors. The resulting encoded payload is assigned to the exploit module's \texttt{payload} attribute. \subsubsection{generate\_single\_payload} \par This method generates an encoded payload using either the supplied payload instance or the exploit's assigned payload instance and returns it to the caller in the form of an \texttt{EncodedPayload} instance. The encoded payload is not assigned as an instance attribute. \subsubsection{regenerate\_payload} \par The \texttt{regenerate\_payload} method is simply a wrapper around the \texttt{generate\_single\_payload} assuming the exploit's payload instance as the first parameter. \subsection{Accessors and Attributes} \par Exploit modules have a number of accessors and attributes that can be used by derived exploits modules to make their lives easier. These accessors and attributes are described below. \subsubsection{compatible\_payloads} \par This method returns an array of payloads that are compatible with the currently selected target, or with all targets if one has not been selected. The array returned is composed of a two-element array that consists of the name of the reference name of the compatible payload and the class associated with the payload. This method takes into account any architecture and platform restrictions specified by the currently selected target, if any. \subsubsection{handler} \par The \texttt{handler} method is used by exploits to pass information on to the associated payload that may be required or useful in detecting if a session has been created. For instance, all find-style payloads require the original connection that was used to trigger the vulnerability. By calling the \texttt{handler} method with the socket that was used, the payload can check and see if a session has been created. \subsubsection{make\_nops} \par In some cases an exploit may need to generate a NOP sled outside of the context of normal encoded payload generation. TO do this, a call can be make to the \texttt{make\_nops} instance method with the length of the sled that should be generated. \subsubsection{nop\_generator} \par This method returns an instance of the first compatible nop generator. \subsubsection{nop\_save\_registers} \par This method returns the selected target's NOP save register information if the \texttt{target} attribute is \texttt{non-nil} and the \texttt{target.save\_register} attribute is \texttt{non-nil}. Otherwise, the module information hash element's \texttt{SaveRegisters} value is returned. \subsubsection{payload} \par This attribute is an instance of a \texttt{Msf::EncodedPayload} after a call has been made to \texttt{generate\_payload}. \subsubsection{payload\_append} \par This method returns the selected target's payload append information if the \texttt{target} attribute is \texttt{non-nil} and the \texttt{target.payload\_append} attribute is \texttt{non-nil}. Otherwise, the value of the \texttt{Append} hash element in the \texttt{payload\_info} hash is returned. \subsubsection{payload\_badchars} \par This method returns the value of the \texttt{BadChars} hash element in the \texttt{payload\_info} hash is returned. \subsubsection{payload\_info} \par This method returns the value of the \texttt{Payload} module information hash element that is used to convey module-specific payload restrictions. \subsubsection{payload\_instance} \par This attribute is set to the payload instance that was used to generate the encoded payload conveyed in the \texttt{payload} attribute. \subsubsection{payload\_max\_nops} \par This method returns the selected target's payload maximum NOP sled length if the \texttt{target} attribute is \texttt{non-nil} and the \texttt{target.payload\_max\_nops} attribute is \texttt{non-nil}. Otherwise, the value of the \texttt{MaxNops} hash element in the \texttt{payload\_info} hash is returned. \subsubsection{payload\_min\_nops} \par This method returns the selected target's payload minimum NOP sled length if the \texttt{target} attribute is \texttt{non-nil} and the \texttt{target.payload\_min\_nops} attribute is \texttt{non-nil}. Otherwise, the value of the \texttt{MinNops} hash element in the \texttt{payload\_info} hash is returned. \subsubsection{payload\_prepend} \par This method returns the selected target's payload append information if the \texttt{target} attribute is \texttt{non-nil} and the \texttt{target.payload\_append} attribute is \texttt{non-nil}. Otherwise, the value of the \texttt{Append} hash element in the \texttt{payload\_info} hash is returned. \subsubsection{payload\_prepend\_encoder} \par This method returns the selected target's payload prepend encoder information if the \texttt{target} attribute is \texttt{non-nil} and the \texttt{target.payload\_prepend\_encoder} attribute is \texttt{non-nil}. Otherwise, the value of the \texttt{PrependEncoder} hash element in the \texttt{payload\_info} hash is returned. \subsubsection{payload\_space} \par This method returns the selected target's payload maximum payload space if the \texttt{target} attribute is \texttt{non-nil} and the \texttt{target.payload\_space} attribute is \texttt{non-nil}. Otherwise, the value of the \texttt{Space} hash element in the \texttt{payload\_info} hash is returned. \subsubsection{stack\_adjustment} \par This method returns the instructions associated with adjusting the stack pointer by a fixed amount in an architecture independent fashion. First, the method looks to see if a target-specific stack adjustment has been specified and if so uses that. Otherwise, the method uses the stack adjustment specified as the value of the \texttt{StackAdjustment} hash element in the \texttt{payload\_info} hash. From there, the method tries to generate the instructions associated with the target or module specific architecture. \subsubsection{target} \par This attribute returns the \texttt{Msf::Target} instance associated with the target index that has been set in the module's datastore through the \texttt{TARGET} option value. If the index is invalid or \texttt{nil}, \texttt{nil} is returned. \par This attribute is typically used by exploits to get target-specific addressing information. \subsection{Mixins} \par One of the major design changes in the 3.0 version of the framework was the introduction of exploit mixins. The purpose of exploits mixins are to reduce, and in most cases eliminate, the duplicated code that is often shared between exploit modules that attempt to leverage vulnerabilities found in specific protocol implementations. The mixins also provide a way to share code that is often used independent of protocols, such as the generation of an SEH registration record during the exploitation of an SEH overwrite. By placing this code in mixins, the framework can augment the support at shared levels and introduce things like normalized evasion without having to modify every existing exploit. Encapsulation is very powerful. \par These mixins are meant to be \texttt{include}'d in exploits that need them. More than one mixin can be included in a single exploit. \par As the framework grows, the number of exploit mixins that can be used by modules will grow as well. This document will attempt to show some of the existing mixins. \subsubsection{Msf::Exploit::Brute} \par The brute force mixin provides a flexible implementation that can be used in a generic fashion for exploits that wish to support brute forcing. This mixin implements the \texttt{exploit} method and detects if the currently selected target is a brute force target. If it is, the mixin does all the required address walking based on target specified start addresses and stop addresses. During each iteration, the mixin calls the \texttt{brute\_exploit} method with the current address state which should be implemented by the derived class. If the \texttt{exploit} method is called with a target that is not intended for brute forcing, the mixin calls the \texttt{single\_exploit} method. \subsubsection{Msf::Exploit::Egghunter} \par The purpose of the egghunter mixin is to encapsulate the generation of an architecture and platform specific egghunter as provided by the \texttt{Rex::Exploitation::Egghunter} class. This feature is provided by the mixin's \texttt{generate\_egghunter} method which takes into account the currently selected target's platform and architecture. \subsubsection{Msf::Exploit::Remote::DCERPC} \par The DCERPC mixin provides methods that are useful to exploits that attempt to leverage vulnerabilities in DCERPC applications. It also provides a unified evasion interface that makes it so any exploits that use the mixin can make use of multi-context bind evasion and packet fragmentation. \par This mixin automatically registers the \texttt{RHOST} and \texttt{RPORT} options. It also registers two advanced options, \texttt{DCEFragSize} and \texttt{DCEMultiBind}. \subsubsection{Msf::Exploit::Remote::Ftp} \par The FTP mixin provides a set of methods that are useful when interacting with an FTP server, such as logging into the server and sending some of the basic commands. This mixin includes the \texttt{Msf::Exploit::Remote::Tcp} mixin. \par This mixin automatically registers the \texttt{RHOST}, \texttt{RPORT}, \texttt{USER}, and \texttt{PASS} options. \subsubsection{Msf::Exploit::Remote::HttpClient} \par The HTTP client mixin wraps some of the methods for creating an instance of a \texttt{Rex::Proto::Http::Client} such that derived exploits can simply call \texttt{connect} on their module instance to establish an HTTP connection to a remote server. This mixin also automatically registers the \texttt{RHOST}, \texttt{RPORT}, and \texttt{VHOST} options. \subsubsection{Msf::Exploit::Remote::HttpServer} \par The HTTP server mixin wraps the creation or re-use of a local HTTP server that is used in the exploitation of HTTP clients, like web-browsers. This mixin also includes the \texttt{Msf::Exploit::Remote::TcpServer} mixin. \subsubsection{Msf::Exploit::Remote::SMB} \par The SMB mixin implements methods that are useful when exploiting vulnerabilities over the SMB protocol. It provides methods for connecting and logging into an SMB server as well as other helper methods for operating on the SMB connection once established. This mixin includes the \texttt{Msf::Exploit::Remote::Tcp} mixin. \par This mixin automatically registers the \texttt{RPORT}, \texttt{SMBDirect}, \texttt{SMBUSER}, \texttt{SMBPASS}, \texttt{SMBDOM}, and \texttt{SMBNAME} options. It also registers the \texttt{SMBPipeWriteMinSize}, \texttt{SMBPipeWriteMaxSize}, \texttt{SMBPipeReadMinSize}, and \texttt{SMBPipeReadMaxSize} advanced options. \subsubsection{Msf::Exploit::Remote::Tcp} \par The TCP mixin implements a basic TCP client interface that can be used in a generic fashion to connect or otherwise communicate with applications that speak over TCP. \par This mixin automatically registers the \texttt{RPORT}, \texttt{RHOST}, and \texttt{SSL} options. \subsubsection{Msf::Exploit::Remote::TcpServer} \par The TCP server mixin implements a basic TCP server that can be used to exploit vulnerabilities in clients that speak over TCP. \par This mixin automatically registers the \texttt{SRVHOST} and \texttt{SRVPORT} options. \subsubsection{Msf::Exploit::Remote::Udp} \par The UDP mixin implements a basic UDP client interface that can be used in a generic fashion to connect or otherwise communicate with applications that speak over UDP. \par This mixin automatically registers the \texttt{RPORT}, \texttt{RHOST}, and \texttt{SSL} options. \subsubsection{Msf::Exploit::Seh} \par The SEH mixin implements some wrapper methods that can be used by exploits that leverage the SEH overwrite exploitation vector. The purpose of this mixin is to wrap the generation of SEH registration records in such a way that it's possible to take into account higher evasion levels. This is accomplish by using the \texttt{Rex::Exploitation::Seh} class. \par This mixin automatically registers the \texttt{DynamicSehRecord} advanced option. \section{Nop} \par NOP generator modules are used to create a string of instructions that have no real affect when executed on a machine other than altering the state of registers or toggling processor flags. All nop modules must inherit from the \texttt{Msf::Nop} base class at some level. Nop modules are fairly simplistic when compared to the other types of modules in the framework. There are only two methods that the framework uses when dealing with nop modules. \subsection{generate\_sled} \par The \texttt{generate\_sled} method performs the action that the name implies. It takes the size of the NOP sled to generate as the first argument and a hash of optional parameters as the second argument. The hash controls some of the behaviors of the NOP generator. The table shown in figure \ref{fig-table-nop-genhash} shows the hash elements that may be passed by the framework to \texttt{generate\_sled}. \begin{figure}[h] \begin{center} \begin{tabular}{|l|l|p{3.0in}|} \hline \textbf{Hash Element} & \textbf{Type} & \textbf{Description} \\ \hline Random & Bool & Indicates that random NOP generation should be used. \\ \hline SaveRegisters & Array & An array of architecture-specific registers that should not be touched by instructions generated in the NOP sled. \\ \hline BadChars & String & The string of bad characters, if any, that should be avoided by the NOP sled. \\ \hline \end{tabular} \caption{\texttt{Msf::Nop} \texttt{generate\_sled} optional hash arguments} \label{fig-table-nop-genhash} \end{center} \end{figure} \par Once sled generation has completed, the return value from \texttt{generate\_sled} the the NOP sled buffer if it succeeds. \subsection{nop\_repeat\_threshold} \par This method simply returns the default number of times to attempt to find a valid NOP byte when generating the NOP sled. The default is \texttt{10000}. This is primarily used as a reference for nop modules during sled generation. \section{Payload} \subsection{Single} \subsection{Stage} \subsection{Stager} \section{Recon} \par The reconnaissance module is still undergoing design review and will not be documented at this time. \chapter{Framework Plugins} \label{framework-plugins} \section{User-interface Plugins} \chapter{Framework Sessions} \label{framework-sessions} \section{Command Shell} \section{Meterpreter} \chapter{Methodologies} \section{Writing an Exploit} \chapter{Conclusion} \appendix \chapter{Samples} \section{Framework Core} \section{Framework Base} \section{Framework Module} \subsection{Encoder} \subsection{Exploit} \subsection{Nop} \subsection{Payload} \subsection{Recon} \section{Framework Plugin} \section{Extended Tools} \end{document}