A target program might behave differently if it is being debugged, sometimes this can be very annoying. Also, these behavior deviations can be leveraged by anti-debugging.IsDebuggerPresent and CheckRemoteDebuggerPresent are well known APIs to tell if a program is attached by a debugger. 0:000> uf KERNELBASE!IsDebuggerPresent KERNELBASE!IsDebuggerPresent:
7512f41b 64a118000000 mov eax,dword ptr fs:[00000018h]
7512f421 8b4030 mov eax,dword ptr [eax+30h]
7512f424 0fb64002 movzx eax,byte ptr [eax+2]
7512f428 c3 retCloseHandle would raise an exception under a debugger, as stated by MSDN:If the application is running under a debugger, the function will throw an exception if it receives either a handle value that is not valid or a pseudo-handle value. Windows heap manager would use debug heap if a program was launched from debugger: The heap manager makes use of FLG_HEAP_ENABLE_TAIL_CHECK, FLG_HEAP_ENABLE_FREE_CHECK and FLG_HEAP_VALIDATE_PARAMETERS flags in PEB!NtGlobalFlags.
Low Fragmentation Heap might be disabled.
Heap functions might throw SEH, an article covering this can be found at debuginfo.com.OutputDebugString, we've have a dedicated topic on it. SetUnhandledExceptionFilter, a decent article can be found at debuginfo.com.NtSetInformationThread can be used to hide (detach) a thread from debugger.In addition, the target program can check its own integrity or the integrity of the system. PEB and TEB, this is exactly what IsDebuggerPresent has used.
DebugPort, this is used by the kernel (EPROCESS). NtQueryInformationProcess from NTDLL can be used to retrieve this information.
INT3 and thread context, as we've already demonstrated here.
Environment variable, parent process, process startup information.
Image File Execution Options.
Call stack and register. If the debugger makes use of func-eval, conditional breakpoints with side effects, or caused some execution flow changes, it can be detected.
Read more: Rubato and Chord
QR:
7512f41b 64a118000000 mov eax,dword ptr fs:[00000018h]
7512f421 8b4030 mov eax,dword ptr [eax+30h]
7512f424 0fb64002 movzx eax,byte ptr [eax+2]
7512f428 c3 retCloseHandle would raise an exception under a debugger, as stated by MSDN:If the application is running under a debugger, the function will throw an exception if it receives either a handle value that is not valid or a pseudo-handle value. Windows heap manager would use debug heap if a program was launched from debugger: The heap manager makes use of FLG_HEAP_ENABLE_TAIL_CHECK, FLG_HEAP_ENABLE_FREE_CHECK and FLG_HEAP_VALIDATE_PARAMETERS flags in PEB!NtGlobalFlags.
Low Fragmentation Heap might be disabled.
Heap functions might throw SEH, an article covering this can be found at debuginfo.com.OutputDebugString, we've have a dedicated topic on it. SetUnhandledExceptionFilter, a decent article can be found at debuginfo.com.NtSetInformationThread can be used to hide (detach) a thread from debugger.In addition, the target program can check its own integrity or the integrity of the system. PEB and TEB, this is exactly what IsDebuggerPresent has used.
DebugPort, this is used by the kernel (EPROCESS). NtQueryInformationProcess from NTDLL can be used to retrieve this information.
INT3 and thread context, as we've already demonstrated here.
Environment variable, parent process, process startup information.
Image File Execution Options.
Call stack and register. If the debugger makes use of func-eval, conditional breakpoints with side effects, or caused some execution flow changes, it can be detected.
Read more: Rubato and Chord
QR:
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