PESPinv13Cyberbob

Hunt Hypothesis

This hypothesis targets the presence of the “Cyberbob” YARA signature, which likely indicates a specific low-severity malware variant or suspicious process behavior within the environment. Proactively hunting for this indicator allows the SOC to identify potentially dormant or early-stage infections that may not yet trigger high-fidelity alerts, enabling timely containment before the adversary establishes a foothold in Azure Sentinel.

YARA Rule

rule PESPinv13Cyberbob
{
      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 AC 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

• Legitimate Application Update via MSI/EXE Installer: Many enterprise applications (e.g., Adobe Creative Cloud, Microsoft Office, or specialized engineering CAD tools) use installers that may contain specific byte patterns or string signatures matching PESPinv13Cyberbob due to embedded libraries or obfuscated update scripts.

  • Filter/Exclusion: Exclude processes where the parent process is a known installer executable (e.g., msiexec.exe, setup.exe, install.exe) and the file path resides in standard installation directories like C:\Program Files\ or C:\Program Files (x86)\.

• Scheduled Backup or Snapshot Utility Execution: Enterprise backup solutions (e.g., Veeam, Commvault, or Windows Server Backup) often spawn child processes to handle file compression or encryption, which might trigger YARA rules if the binary contains specific cryptographic or compression library signatures.

  • Filter/Exclusion: Exclude events where the process name matches known backup agents (e.g., vssadmin.exe, wbadmin.exe, veeamagent.exe) and the process was initiated by a scheduled task or service account (e.g., NT AUTHORITY\SYSTEM or a dedicated backup service account).

• Antivirus/Endpoint Protection Real-Time Scanning: Security tools like CrowdStrike Falcon, Microsoft Defender for Endpoint, or SentinelOne perform deep file scans and may load temporary copies of scanned files into memory or create short-lived helper processes that match the YARA signature.

  • Filter/Exclusion: Exclude processes where the parent process is a known EDR/AV agent (e.g., FalconSensor.exe, MsMpEng.exe, SentinelOneAgent.exe) and the file location is in a temporary or quarantine directory (e.g., C:\ProgramData\McAfee\, `C:\Program Files\Microsoft