CsrGetProcessID
Created the Monday 18 March 2019. Updated 3 years, 6 months ago.
This function is undocumented within OpenProcess. It can be used to get the PID of CRSS.exe, which is a SYSTEM process. By default, a process has the SeDebugPrivilege privilege in their access token disabled.
However, when the process is loaded by a debugger such as OllyDbg or WinDbg, the SeDebugPrivilege privilege is enabled. If a process is able to open CRSS.exe process, it means that the process SeDebugPrivilege enabled in the access token, and thus, suggesting that the process is being debugged.
If we call OpenProcess and pass the ID returned by CsrGetProcessId, no error will occur if the SeDebugPrivilege has been set with SetPrivilege / AdjustTokenPrivileges.
Technique Identifier
Technique Tag
Code Snippets
#include <stdio.h>
#include <windows.h>
typedef HANDLE (*_CsrGetProcessId)();
int main(void)
{
HMODULE nt=GetModuleHandle("ntdll.dll");
_CsrGetProcessId CsrGetProcessId=(_CsrGetProcessId)GetProcAddress(nt,"CsrGetProcessId");
HANDLE proc = OpenProcess(PROCESS_ALL_ACCESS,FALSE,CsrGetProcessId());
if(!proc)
{
printf("debugger is present!");
}
}Detection Rules
rule Detect_CsrGetProcessID: AntiDebug {
meta:
description = "Detect CsrGetProcessID as anti-debug"
author = "Unprotect"
comment = "Experimental rule"
strings:
$1 = "CsrGetProcessID" fullword ascii
$2 = "GetModuleHandle" fullword ascii
condition:
uint16(0) == 0x5A4D and filesize < 1000KB and 2 of them
}