CrinklerV01V02RuneLHStubbeandAskeSimonChristensen

Hunt Hypothesis

This detection identifies the execution of a specific file pattern associated with the CrinklerV01V02 malware family, which often indicates early-stage reconnaissance or lateral movement activities by an adversary. Proactively hunting for this signature in Azure Sentinel allows the SOC team to validate potential false positives and uncover stealthy infection vectors that may not trigger high-severity alerts due to their low initial impact.

YARA Rule

rule CrinklerV01V02RuneLHStubbeandAskeSimonChristensen
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B9 [4] 01 C0 68 [4] 6A 00 58 50 6A 00 5F 48 5D BB 03 00 00 00 BE [4] E9 }

condition:
		$a0 at pe.entry_point
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 3-5 specific false positive scenarios for the CrinklerV01V02RuneLHStubbeandAskeSimonChristensen detection rule, formatted as requested:

• Scenario: Microsoft Defender Antivirus (MSRT) Scheduled Scans

  • Context: The YARA rule likely matches signatures associated with the Crinkler malware family. However, Microsoft Defender’s real-time protection and scheduled “Quick Scan” jobs often utilize similar heuristic patterns or load specific DLLs that trigger this signature during routine maintenance windows (e.g., 02:00 AM daily).
  • Filter/Exclusion: Create a process exclusion for MsMpEng.exe and its child processes. Additionally, add an IP-based exclusion if the scan originates from a known management server (e.g., 192.168.10.5) during off-hours.

• Scenario: Sysinternals Process Monitor or ProcMon Background Analysis

  • Context: Security analysts frequently run Sysinternals tools like Procmon.exe to audit file system and registry activity. These tools often inject hooks into running processes to monitor behavior, which can mimic the memory footprint or API call patterns of the Crinkler stubs detected by this rule.
  • Filter/Exclusion: Exclude any process where the command line contains sysinternals.com or the executable path is located within C:\Program Files\Sysinternals\. A specific filter could be: ProcessName IN ("Procmon.exe", "PsExec.exe") AND Path STARTS_WITH "C:\Program Files\Sysinternals\".

• Scenario: Jenkins CI/CD Pipeline Artifact Generation

  • Context: In DevOps environments, the Jenkins build agent often compiles and packages applications. During the artifact generation phase, temporary stub