AddVectoredExceptionHandler

Created the Friday 10 March 2023. Updated 1 year, 2 months ago.

The AddVectoredExceptionHandler technique is an anti-debugging method that can detect the presence of debuggers using Vectored Exception Handlers. This technique works by calling AddVectoredExceptionHandler(1, ourHandler) to register a top-level exception handler that will catch any exceptions raised by the process, including those generated by debuggers.

After this call has taken place, stepping through the code will trigger an EXCEPTION_SINGLE_STEP exception, which is caught by our top-level handler. This exception is typically only generated by debuggers and is therefore a strong indicator that a debugger is present.

Technique Identifier

U0125

Technique Tags

Anti-debugging Vectored Exception Handlers AddVectoredExceptionHandler Debugging Exception handling EXCEPTION_SINGLE_STEP

Featured Windows API's

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AddVectoredExceptionHandler

Code Snippets

Description

This code is an example of using the AddVectoredExceptionHandler function to register a top-level exception handler in a Windows program. The goal of this handler is to detect the presence of VEH (Vectored Exception Handler) debuggers, which can be used to step through code and inspect the program's memory.

The main function of the code calls the AddVectoredExceptionHandler function, which registers the TopLevelHandler function as the top-level exception handler. The first parameter to AddVectoredExceptionHandler is 1, which means that this handler will be the first one to be called.

The TopLevelHandler function takes an EXCEPTION_POINTERS pointer as its parameter, which contains information about the exception that was raised. If the exception code is EXCEPTION_SINGLE_STEP, this means that a VEH debugger has single-stepped through the code, and the CaughtVEHDebugger flag is set to true.

Finally, the main function prints whether the VEH debugger was caught or not based on the value of the CaughtVEHDebugger flag. If the flag is true, this means that a VEH debugger was detected, and the program prints "Caught VEH debugger: true". If the flag is false, this means that no VEH debugger was detected, and the program prints "Caught VEH debugger: false".

//github: alsch092
#include <windows.h>
#include <stdio.h>

bool CaughtVEHDebugger = false;

LONG CALLBACK TopLevelHandler(EXCEPTION_POINTERS* info)
{
    if (info->ExceptionRecord->ExceptionCode == EXCEPTION_SINGLE_STEP) //Detects when a VEH debugger single-steps through code
        CaughtVEHDebugger = true;

    printf("Executed toplevelhandler, Exception: %X\n", info->ExceptionRecord->ExceptionCode); //print any other exceptions we encounter
    return EXCEPTION_CONTINUE_SEARCH;
}

int main()
{
    AddVectoredExceptionHandler(1, TopLevelHandler);

    if (CaughtVEHDebugger)
        printf("Caught VEH debugger: %s\n", ((CaughtVEHDebugger > 0) ? "true" : "false"));

    return 0;
}

About Author Open Snippet

Author: Alex Schwarz / Target Platform: Windows

Additional Resources

External Links

The resources provided below are associated links that will give you even more detailed information and research on current evasion technique. It is important to note that, while these resources may be helpful, it is important to exercise caution when following external links. As always, be careful when clicking on links from unknown sources, as they may lead to malicious content.

AddVectoredExceptionHandler function (errhandlingapi.h) - Win32 apps | Microsoft Learn