CsrGetProcessID

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

U0115

Technique Tag

CsrGetProcessID

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.

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 
}

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.

https://www.gironsec.com/blog/2013/12/other-antidebug-tricks/