Unhandled Exception Filter

Created the Monday 18 March 2019. Updated 3 years, 6 months ago.

An application-defined function that passes unhandled exceptions to the debugger, if the process is being debugged. Otherwise, it optionally displays an application error message box and causes the exception handler to be executed.

If an exception occurs and no exception handler is registered, the UnhandledExceptionFilter function will be called. It is possible to register a custom unhandled exception filter using the SetUnhandledExceptionFilter. But if the program is running under a debugger, the custom filter won’t be called, and the exception will be passed to the debugger.

Therefore, if the unhandled exception filter is registered and the control is passed to it, then the process is not running with a debugger.

Technique Identifier


Technique Tag


Code Snippets

#include "pch.h"
#include "UnhandledExceptionFilter_Handler.h"

When an exception occurs, and no registered Exception Handlers exist (neither Structured nor
Vectored), or if none of the registered handlers handles the exception, then the kernel32
UnhandledExceptionFilter() function will be called as a last resort. 

BOOL bIsBeinDbg = TRUE;

LONG WINAPI UnhandledExcepFilter(PEXCEPTION_POINTERS pExcepPointers)
	// If a debugger is present, then this function will not be reached.
	bIsBeinDbg = FALSE;

BOOL UnhandledExcepFilterTest ()
	LPTOP_LEVEL_EXCEPTION_FILTER Top = SetUnhandledExceptionFilter(UnhandledExcepFilter);
	return bIsBeinDbg;

Detection Rules

rule Detect_SuspendThread: AntiDebug {
        description = "Detect SuspendThread as anti-debug"
        author = "Unprotect"
        comment = "Experimental rule"
        $1 = "UnhandledExcepFilter" fullword ascii
        $2 = "SetUnhandledExceptionFilter" fullword ascii
       uint16(0) == 0x5A4D and filesize < 1000KB and any of them 

Additional Resources

External Links

Subscribe to our Newsletter

The information entered into this form is mandatory. It will be subjected to computer processing. It is processed by computer in order to support our users and readers. The recipients of the data will be : contact@unprotect.it.

According to the Data Protection Act of January 6th, 1978, you have at any time, a right of access to and rectification of all of your personal data. If you wish to exercise this right and gain access to your personal data, please write to Thomas Roccia at contact@unprotect.it.

You may also oppose, for legitimate reasons, the processing of your personal data.