PESpinv13betaCyberbob

Hunt Hypothesis

This hypothesis targets the execution of the specific binary “PESpinv13betaCyberbob,” which likely indicates the deployment of a low-severity, potentially experimental or beta-stage tooling often used for initial access or lateral movement. Proactively hunting for this artifact in Azure Sentinel allows the SOC to identify early-stage adversary activity or benign test deployments that may be overlooked by standard high-fidelity detections, ensuring visibility into unique or emerging threat tooling within the environment.

YARA Rule

rule PESpinv13betaCyberbob
{
      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 71 DF 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
}

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 developer or DevOps engineer is running a local build pipeline that compiles a C++ application using the Microsoft Visual C++ Compiler (cl.exe) or MSBuild, where the compiler generates intermediate object files or debug symbols that match the heuristic pattern for “Cyberbob” (likely a placeholder for a specific PE header anomaly or version string check).
  • Filter/Exclusion: Exclude processes where the parent process is MSBuild.exe, cl.exe, or vstest.console.exe, and the file path contains \bin\ or \obj\ directories.
• Scenario: An IT administrator is deploying a legacy application update via Group Policy or a configuration management tool (e.g., SCCM/MECM) that temporarily stages a PE binary in the C:\Windows\Temp or C:\Users\Public directory for installation, which may have an unusual version resource or missing digital signature that triggers the “Spin” heuristic.
  • Filter/Exclusion: Exclude events where the file path is under C:\Windows\Temp, C:\Users\Public, or C:\ProgramData and the process name is msiexec.exe, setup.exe, or install.exe.
• Scenario: A security team is performing a controlled test or using a tool like PE-sieve or Detect-IT to analyze a known benign binary for research purposes, where the tool intentionally modifies or inspects the PE header in a way that mimics the “Cyberbob” signature.
  • Filter/Exclusion: Exclude processes where the parent process is powershell.exe or cmd.exe and the command line contains arguments like -scan, -dump, or -analyze, or where the user account is a dedicated service account (e.g., svc_security_test).
• Scenario: A Java or