PESpin V07 cyberbobnbsp nbsp SignByfly 20080312

Hunt Hypothesis

This YARA rule targets specific PE file characteristics associated with the “PESpin” family, potentially indicating the presence of legacy or obfuscated executables that may be used for initial access or persistence. Proactively hunting for these signatures in Azure Sentinel allows the SOC to identify dormant or low-noise malware artifacts that standard behavioral detections might miss, ensuring comprehensive coverage of the endpoint attack surface.

YARA Rule

rule PESpin_V07_cyberbobnbsp_nbsp_SignByfly_20080312: PEiD
{
    strings:
        $a = { EB 01 ?? 60 E8 00 00 00 00 8B 1C 24 83 C3 12 81 2B E8 B1 06 00 FE 4B FD 82 2C 24 83 D5 46 00 0B E4 74 9E 75 01 ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? 19 77 00 43 B7 F6 C3 6B B7 00 00 F9 FF E3 C9 C2 08 00 ?? ?? ?? ?? ?? 5D 33 C9 41 E2 17 EB 07 ?? ?? ?? ?? ?? ?? ?? E8 01 00 00 00 ?? 5A 83 EA 0B FF E2 EB 04 ?? EB 04 00 EB FB FF 8B ?? ?? ?? ?? ?? 8B 42 3C 03 C2 89 ?? ?? ?? ?? ?? EB 01 ?? 41 C1 E1 07 8B 0C 01 03 CA E8 03 00 00 00 EB 04 ?? EB FB ?? 83 04 24 0C C3 }
    condition:
        $a 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

• Legacy .NET Framework Installer Execution: The rule likely targets specific byte patterns or string signatures associated with older PE spinners or packers (e.g., UPX, FSG, or custom spinners used in 2008-era software). Legitimate enterprise applications, particularly those built on the .NET 1.1 or 2.0 framework (common in legacy ERP systems like SAP or older versions of Microsoft Office), may use these spinners for size optimization.

  • Filter/Exclusion: Exclude files located in standard application directories (e.g., C:\Program Files\, C:\Program Files (x86)\) where the parent process is a known service host (e.g., svchost.exe, w3wp.exe) or a specific legacy application binary (e.g., sqlservr.exe, oracle.exe).

• Scheduled Backup or Archiving Jobs: Enterprise backup solutions (e.g., Veeam, Commvault, or Windows Server Backup) often compress or pack data files before transfer. If the backup agent uses a PE-based compression utility or if the rule matches the header of compressed archives that retain PE structure, this can trigger false positives during nightly scheduled tasks.

  • Filter/Exclusion: Exclude executions where the command line contains backup-related keywords (e.g., /backup, /archive, /compress) or where the process name matches known backup agents (e.g., vssadmin.exe, wbadmin.exe, commvault.exe).

• Third-Party Antivirus or EDR Quarantine Scans: Some endpoint protection tools or disk imaging utilities (e.g., Acronis, Symantec) create temporary PE-based containers or use spinner-like structures for on-the-fly scanning and restoration. These temporary files, often created in C:\Windows\Temp or C:\Users\Public\Documents, may match