PEtitev22

Hunt Hypothesis

This YARA rule targets specific characteristics of the PEtitev22 malware family, which often leverages fileless or in-memory techniques to establish persistence and execute malicious payloads. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify compromised endpoints early, mitigating the risk of lateral movement or data exfiltration before the low-severity threat escalates.

YARA Rule

rule PEtitev22
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B8 [4] 68 [4] 64 FF 35 [4] 64 89 25 [4] 66 9C 60 50 }

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

• Scenario: A legacy Java application server (e.g., Apache Tomcat or WildFly) is updated via a standard patching cycle, where the installer temporarily writes a new JAR file to the application directory before replacing the old one. The YARA rule PEtitev22 may match the intermediate state of the file or the specific bytecode patterns in the updated library.
  • Filter/Exclusion: Exclude files located in standard Java application directories (e.g., C:\Program Files\Apache Tomcat\*, C:\opt\tomcat\*) or filter by file extension .jar and .war if the rule primarily targets PE executables but has broad matching. Alternatively, add an exclusion for known vendor hashes associated with the specific Java runtime version.
• Scenario: An enterprise endpoint protection agent (e.g., CrowdStrike Falcon, Carbon Black, or Defender for Endpoint) performs a real-time scan and creates a temporary copy of a running executable in a shadow directory (e.g., %TEMP% or a specific vendor cache folder) to analyze its behavior. The YARA rule matches the temporary copy, which is a legitimate artifact of the security tool’s operation.
  • Filter/Exclusion: Exclude paths containing common temporary or cache directories for EDR tools (e.g., C:\ProgramData\CrowdStrike\*, C:\Program Files\Windows Defender\*, C:\Users\%USERNAME%\AppData\Local\Temp\*). Ensure the exclusion applies to files with specific vendor-related names or parent processes like FalconSensor.exe or MsMpEng.exe.
• Scenario: A developer or IT administrator runs a custom PowerShell script or a .NET-based utility (e.g., a custom internal tooling app) that dynamically loads a compiled DLL or EXE from a shared network drive or a specific development folder. The Y