PESpinv03Engcyberbob

Hunt Hypothesis

This rule targets the presence of the “PESpinv03Engcyberbob” YARA signature, which likely identifies a specific low-severity executable or script associated with a known malware family or tooling. Proactively hunting for this indicator allows the SOC to detect early-stage or dormant threats that may not yet trigger high-fidelity alerts, ensuring timely containment of potential compromise within the Azure Sentinel environment.

YARA Rule

rule PESpinv03Engcyberbob
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 01 68 60 E8 00 00 00 00 8B 1C 24 83 C3 12 81 2B E8 B1 06 00 FE 4B FD 82 2C 24 B7 CD 46 }
	$a1 = { EB 01 68 60 E8 00 00 00 00 8B 1C 24 83 C3 12 81 2B E8 B1 06 00 FE 4B FD 82 2C 24 B7 CD 46 00 0B E4 74 9E 75 01 C7 81 73 04 D7 7A F7 2F 81 73 19 77 00 43 B7 F6 C3 6B B7 00 00 F9 FF E3 C9 C2 08 00 A3 68 72 01 FF 5D 33 C9 41 E2 17 EB 07 EA EB 01 EB EB 0D FF }

condition:
		$a0 at pe.entry_point or $a1 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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: A developer or DevOps engineer uses a legitimate commercial code obfuscation tool (e.g., Dotfuscator for .NET or UPX for native binaries) to reduce the size of a custom internal microservice or CLI utility before deployment to a staging environment. The YARA rule PESpinv03Engcyberbob likely targets specific byte patterns or entropy characteristics common in obfuscated or packed executables, causing the clean, optimized binary to match the signature.

  • Filter/Exclusion: Exclude files located in specific development or build artifact directories (e.g., C:\Builds\, D:\Artifacts\) or exclude binaries where the PE header indicates a known compiler (e.g., MSVC or GCC) and the file size is below a certain threshold (e.g., < 5MB), unless the file is executed from a user profile directory.

• Scenario: An IT administrator installs a new version of a widely used enterprise application (e.g., Adobe Creative Cloud, Zoom, or Slack) that includes a custom installer or updater component. These components are often packed or protected by vendor-specific packers to prevent tampering, which can trigger generic “packed/obfuscated PE” YARA rules. The rule may misidentify the vendor’s standard packing technique as malicious because it matches the PESpinv03Engcyberbob pattern.

  • Filter/Exclusion: Create an allowlist for known vendor-specific executable paths (e.g., C:\Program Files\Adobe\, C:\Program Files\Zoom\) or exclude files where the digital signature is valid and issued by a trusted CA (e.g., Adobe, Zoom, Slack) and the signer matches a known enterprise certificate.

• Scenario: A data science team uses Python or Go to