Debug Registers, Hardware Breakpoints

Created the Friday 13 November 2020. Updated 1 month ago.

Hardware breakpoints allow a debugger to pause execution at specific memory addresses without modifying the program code. They are stored in special CPU registers (DR0 through DR3 on Intel CPUs).

For anti-debugging, malware can inspect the values of these debug registers. If any of the registers contain a non-empty value, it indicates that a hardware breakpoint has been set by a debugger.

A common way to capture this information is by calling RtlCaptureContext(), which retrieves the current thread’s execution context, including the debug registers. The malware can then check DR0–DR3. If one of them is populated, it signals the presence of an active debugger using hardware breakpoints.

Technique Identifiers

U0127 B0001.005

Technique Tag

DR0

Code Snippets

#include <windows.h>
#include <stdio.h>

int main() {

    HANDLE thread = GetCurrentThread();
    CONTEXT threadContext;
    int errorCode;

    memset(&threadContext, 0, sizeof(CONTEXT));
    threadContext.ContextFlags = CONTEXT_ALL;

    if( !GetThreadContext(thread, &threadContext) ){
        errorCode = GetLastError();
        puts("Could not get thread context");
        return errorCode;
    }

    if( threadContext.Dr0 || threadContext.Dr1 || threadContext.Dr2 || threadContext.Dr3 ){
        puts("Detected");
    }
    else{
        puts("Undetected");
    }

    return 0;
}

About Author Open Snippet

Author: Lexsek / Target Platform: Windows

import ctypes
import struct

def detect_breakpoints():
    context = ctypes.create_string_buffer(0x4C)
    context_ptr = ctypes.byref(context)
    context_offset = struct.calcsize("Q") * 6
    ctypes.windll.kernel32.RtlCaptureContext(context_ptr)
    dr0, dr1, dr2, dr3 = struct.unpack_from("4Q", context.raw, context_offset)
    if dr0 or dr1 or dr2 or dr3:
        print("detected hardware breakpoint")

About Author Open Snippet

Author: Matteo Lodi (MatteoLodi) / Target Platform: Windows

Detection Rules

rule:
  meta:
    name: check for hardware breakpoints
    namespace: anti-analysis/anti-debugging/debugger-detection
    author: michael.hunhoff@fireeye.com
    scope: function
    mbc:
      - Anti-Behavioral Analysis::Debugger Detection::Hardware Breakpoints [B0001.005]
    references:
      - https://github.com/LordNoteworthy/al-khaser/blob/master/al-khaser/AntiDebug/HardwareBreakpoints.cpp
    examples:
      - al-khaser_x86.exe_:0x42035D
  features:
    - and:
      - api: kernel32.GetThreadContext
      - number: 0x10010 = CONTEXT_DEBUG_REGISTERS
      - offset: 0x4 = DR0
      - offset: 0x8 = DR1
      - offset: 0xC = DR2
      - offset: 0x10 = DR3
      - count(mnemonic(cmp)): 4 or more

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.