Heap Flag

Created the Monday 18 March 2019. Updated 3 months, 1 week ago.

ProcessHeap is located at 0x18 in the PEB structure. This first heap contains a header with fields used to tell the kernel whether the heap was created within a debugger. The heap contains two fields which are affected by the presence of a debugger. These fields are Flags and ForceFlags.

The values of Flags and ForceFlags are normally set to HEAP_GROWABLE and 0, respectively.

On 64-bit Windows XP, and Windows Vista and higher, if a debugger is present, the Flags field is set to a combination of these flags:

HEAP_GROWABLE (2)
HEAP_TAIL_CHECKING_ENABLED (0x20)
HEAP_FREE_CHECKING_ENABLED (0x40)
HEAP_VALIDATE_PARAMETERS_ENABLED (0x40000000)

When a debugger is present, the ForceFlags field is set to a combination of these flags:

HEAP_TAIL_CHECKING_ENABLED (0x20)
HEAP_FREE_CHECKING_ENABLED (0x40)
HEAP_VALIDATE_PARAMETERS_ENABLED (0x40000000)

Technique Identifiers

U0112 B0001.021

Technique Tag

heapflag

Code Snippets

Description

Original source code available here: https://anti-debug.checkpoint.com/techniques/debug-flags.html#manual-checks-heap-flags

bool Check()
{
#ifndef _WIN64
    PPEB pPeb = (PPEB)__readfsdword(0x30);
    PVOID pHeapBase = !m_bIsWow64
        ? (PVOID)(*(PDWORD_PTR)((PBYTE)pPeb + 0x18))
        : (PVOID)(*(PDWORD_PTR)((PBYTE)pPeb + 0x1030));
    DWORD dwHeapFlagsOffset = IsWindowsVistaOrGreater()
        ? 0x40
        : 0x0C;
    DWORD dwHeapForceFlagsOffset = IsWindowsVistaOrGreater()
        ? 0x44 
        : 0x10;
#else
    PPEB pPeb = (PPEB)__readgsqword(0x60);
    PVOID pHeapBase = (PVOID)(*(PDWORD_PTR)((PBYTE)pPeb + 0x30));
    DWORD dwHeapFlagsOffset = IsWindowsVistaOrGreater()
        ? 0x70 
        : 0x14;
    DWORD dwHeapForceFlagsOffset = IsWindowsVistaOrGreater()
        ? 0x74 
        : 0x18;
#endif // _WIN64

    PDWORD pdwHeapFlags = (PDWORD)((PBYTE)pHeapBase + dwHeapFlagsOffset);
    PDWORD pdwHeapForceFlags = (PDWORD)((PBYTE)pHeapBase + dwHeapForceFlagsOffset);
    return (*pdwHeapFlags & ~HEAP_GROWABLE) || (*pdwHeapForceFlags != 0);
}

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Additional Resources

External Links

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