Vmt hook class2/19/2023 ![]() ![]() Int retValue = MessageBoxW(hWnd, lpText, lpCaption, uiType) // get return value of original function Memcpy(pOrigMBAddress, oldBytes, SIZE) // restore backup VirtualProtect((LPVOID)pOrigMBAddress, SIZE, myProtect, NULL) // assign read write protection Int WINAPI MyMessageBoxW(HWND hWnd, LPCWSTR lpText, LPCWSTR lpCaption, UINT uiType) VirtualProtect((LPVOID)pOrigMBAddress, SIZE, oldProtect, NULL) // reset protection Memcpy(pOrigMBAddress, JMP, SIZE) // set jump instruction at the beginning of the original function Memcpy(&JMP, &JMPSize, 4) // fill the nop's with the jump distance (JMP,distance(4bytes),RET) ![]() Memcpy(oldBytes, pOrigMBAddress, SIZE) // make backup ![]() VirtualProtect((LPVOID)pOrigMBAddress, SIZE, // assign read write protection Memcpy(JMP, tempJMP, SIZE) // store jmp instruction to JMPĭWORD JMPSize = ((DWORD)newFunction - (DWORD)pOrigMBAddress - 5) // calculate jump distance PMessageBoxW pOrigMBAddress = NULL // address of originalīYTE JMP = // 0圎9 = JMP 0x90 = NOP oxC3 = RET Int WINAPI MyMessageBoxW(HWND, LPCWSTR, LPCWSTR, UINT) // Our detour Typedef int (WINAPI *pMessageBoxW)(HWND, LPCWSTR, LPCWSTR, UINT) // Messagebox protoype In the BeginRedirect function, an unconditional relative jump (JMP) opcode (0圎9) instruction will contain the distance to jump to. Once this DLL is injected, it will get the address of the MessageBoXW function from user32.dll, and then the hooking begins. For this example, I chose to hook the MessageBoxW function. All of this resides in a DLL that will be injected into a process. This is the framework of a standard API hook. In 2003 Jonathan Rentzsch showed ways of detouring in MAC-OSX and released mach_star, but this method is way easier. In this example I've detoured fopen from a test program. Since MAC-OSX is also UNIX based it's almost exactly the same as in Linux, only they have renamed LD_PRELOAD to DYLD_INSERT_LIBRARIES and. It is exactly the same as MAC-OSX (see below) but use LD_PRELOAD instead of DYLD_INSERT_LIBRARIES . When you make a twin brother of a function that is defined in an existing shared library, put it in your shared library, and you register your shared library name in DYLD_INSERT_LIBRARIES, your function is used instead of the original one. ![]() UNIX offers a simple way to override functions in a shared library with the LD_PRELOAD environment variable. See Appendix A below for more information. However on Windows systems there is no such thing as LD_PRELOAD, to achieve the same result we must use a little exploit called DLL Injection (On Windows shared libraries are. Function and other symbol definitions in the specified libraries will be used instead of the original ones. On UNIX platforms (Linux/MAC-OSX) this can be achieved using the LD_PRELOAD environment variable, which instructs the loader to load the specific shared libraries. To change code in another process we must load our own shared library in the address space of the other process. This has advantages. For instance on some systems, applications were often only a few hundred kilobytes in size and loaded quickly the majority of their code was located in libraries that had already been loaded for other purposes by the operating system. If virtual memory is used, processes execute the same physical page of RAM, mapped into the different address spaces of each process. Library code may be shared in memory by multiple processes as well as on disk. §1 Shared Libraries & Injection/Loading Shared libraries are code objects that may be loaded during execution into the memory space associated with a process. Please note that i don't claim that these techniques are the best solutions for all cases.Īppendix B: Import Address Table Hooking (IAT)Īppendix E: Example : hiding process(es) under windows Here i will present the techniques i use for the different operating systems. In these cases when one does not have the source code available for the program, it is still possible to modify the code. For example, it might be necessary to instrument the application for performance analysis or to add additional features to a program. Specifically, one might want to intercept calls of certain functions to execute custom code before or after the execution of the original code, or one might want to retrieve or modify the parameters passed to a function. Oftentimes, it can be useful to modify the behavior of an application without making extensive changes to the source code of the application. ![]()
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