Debugger Evasion

What the technique is

Adversaries may employ various means to detect and avoid debuggers. Debuggers are typically used by defenders to trace and/or analyze the execution of potential malware payloads. Debugger evasion may include changing behaviors based on the results of the checks for the presence of artifacts indicative of a debugged environment. Similar to Virtualization/Sandbox Evasion, if the adversary detects a debugger, they may alter their malware to disengage from the victim or conceal the core functions of the implant. They may also search for debugger artifacts before dropping secondary or additional payloads. Specific checks will vary based on the target and/or adversary. On Windows, this may involve Native API function calls such as IsDebuggerPresent() and NtQueryInformationProcess(), or manually checking the BeingDebugged flag of the Process Environment Block (PEB). On Linux, this may involve querying /proc/self/status for the TracerPID field, which indicates whether or not the process is being traced by dynamic analysis tools. Other checks for debugging artifacts may also seek to enumerate hardware breakpoints, interrupt assembly opcodes, time checks, or measurements if exceptions are raised in the current process (assuming a present debugger would “swallow” or handle the potential error). […]

What MITRE says you would watch

• AN1045

  Monitor for suspicious use of Windows API calls such as IsDebuggerPresent() and NtQueryInformationProcess(), or processes manually checking the BeingDebugged flag in the Process Environment Block (PEB). Detect sequences of OutputDebugStringW() calls in short intervals that may indicate debugger flooding attempts.

• AN1046

  Monitor access to /proc/self/status where TracerPID field is queried, as this is a common technique for debugger detection. Detect processes that attempt to trigger exceptions intentionally and monitor whether exception handling indicates presence of a debugger.

• AN1047

  Detect suspicious calls to sysctl or ptrace API used to determine if a process is being debugged. Monitor for processes that flood OutputDebugString equivalents or generate abnormal exceptions to evade analysis.