Heap Flag

Created the Monday 18 March 2019. Updated 6 months, 2 weeks 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

Featured Windows API's

Below, you will find a list of the most commonly used Windows API's that are currently utilized by malware authors for current evasion technique. This list is meant to provide an overview of the API's that are commonly used for this purpose. If there are any API's that you feel should be included on this list, please do not hesitate to contact us. We will be happy to update the list and provide any additional information or documentation that may be helpful.

IsWindow

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);
}

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.