NtGlobalFlag

The information that the system uses to determine how to create heap structures is stored at an undocumented location in the PEB at offset 0x68. If the value at this location is 0x70, we know that we are running in a debugger.

U0111

Code Snippets

#include <Winternl.h>
#include <Windows.h>
#include <tchar.h>
#include <stdio.h>

/*
*Using ZwQueryInformationProcess we get the PEB Address and 
*then we check the NtGlobalFlag to determine the process is being debugged or not.
*/

int main() {
     
    typedef unsigned long(__stdcall *pfnZwQueryInformationProcess)
    (
        IN  HANDLE,
        IN  unsigned int, 
        OUT PVOID, 
        IN  ULONG, 
        OUT PULONG
    );
    pfnZwQueryInformationProcess ZwQueryInfoProcess = NULL;
     
    HMODULE hNtDll = LoadLibrary(_T("ntdll.dll"));
    if (hNtDll == NULL) { }
 
    ZwQueryInfoProcess = (pfnZwQueryInformationProcess) GetProcAddress(hNtDll,
        "ZwQueryInformationProcess");
    if (ZwQueryInfoProcess == NULL) { }
    unsigned long status;
 
    DWORD pid = GetCurrentProcessId();
    HANDLE hProcess = OpenProcess(PROCESS_QUERY_INFORMATION, FALSE, pid);
    PROCESS_BASIC_INFORMATION pbi;
    status = ZwQueryInfoProcess(hProcess,
                                ProcessBasicInformation,
                                &pbi,
                                sizeof(pbi),
                                NULL);
                                 
    PPEB peb_addr = pbi.PebBaseAddress;
    DWORD ptr = pbi.PebBaseAddress;
    ptr|=104;
    DWORD *temp = ptr;
    MessageBox(0, *temp ? "Debugger found" : "Debugger not found","Status",0x30);
     
    return 0;
}

Detection Rules

rule DebuggerCheck__GlobalFlags  {
    meta:
	description = "Rule to detect NtGlobalFlags debugger check"
        author = "Thibault Seret"
        date = "2020-09-26"
    strings:
        $s1 = "NtGlobalFlags"
    condition:
        any of them
}
rule:
  meta:
    name: check for PEB NtGlobalFlag flag
    namespace: anti-analysis/anti-debugging/debugger-detection
    author: moritz.raabe@fireeye.com
    scope: function
    mbc:
      - Anti-Behavioral Analysis::Debugger Detection::Process Environment Block NtGlobalFlag [B0001.036]
    references:
      - Practical Malware Analysis, Chapter 16, p. 355
      - https://www.geoffchappell.com/studies/windows/win32/ntdll/structs/peb/index.htm
    examples:
      - Practical Malware Analysis Lab 16-01.exe_:0x403530
  features:
    - and:
      - basic block:
        - and:
          - match: PEB access
          - or:
            - or:
              - offset/x32: 0x68 = PEB.NtGlobalFlag
              - offset/x64: 0xBC = PEB.NtGlobalFlag
            - and:
              - mnemonic: add
              - or:
                - number/x32: 0x68 = PEB.NtGlobalFlag
                - number/x64: 0xBC = PEB.NtGlobalFlag
      - number: 0x70 = (FLG_HEAP_ENABLE_TAIL_CHECK | FLG_HEAP_ENABLE_FREE_CHECK | FLG_HEAP_VALIDATE_PARAMETERS)

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