PeCompact2253276BitSumTechnologies

Hunt Hypothesis

This YARA rule targets specific PE file characteristics associated with BitSum Technologies, potentially indicating the presence of specialized or obfuscated binaries that may be leveraged for initial access or persistence. Proactively hunting for these signatures in Azure Sentinel allows the SOC team to identify low-severity indicators of compromise early, ensuring that subtle adversary footholds are detected before they escalate into more significant threats.

YARA Rule

rule PeCompact2253276BitSumTechnologies
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B8 [4] 55 53 51 57 56 52 8D 98 C9 11 00 10 8B 53 18 52 8B E8 6A 40 68 00 10 00 00 FF 73 04 6A 00 8B 4B 10 03 CA 8B 01 FF D0 5A 8B F8 50 52 8B 33 8B 43 20 03 C2 8B 08 89 4B 20 8B 43 1C 03 C2 8B 08 89 4B 1C 03 F2 8B 4B 0C 03 CA 8D 43 1C 50 57 56 FF }

condition:
		$a0
}

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 Use of 7-Zip or WinRAR for Archive Creation/Extraction

  • Scenario: Administrators or developers frequently use 7z.exe or WinRAR.exe to compress logs, deploy software packages, or extract vendor-provided archives. The YARA rule likely matches the specific bit-sum signature or header structure of these compacted PE files, triggering alerts on standard file operations.
  • Filter/Exclusion: Exclude processes where the parent image is 7z.exe, WinRAR.exe, or WinRAR.exe (case-insensitive), or exclude file paths ending in .7z, .rar, or .zip if the rule is file-based.

• Scheduled Task Execution of Third-Party Maintenance Scripts

  • Scenario: Enterprise scheduled tasks (e.g., Task Scheduler jobs) run maintenance scripts or small utility binaries (often compiled with compactors like UPX or similar) for log rotation, database backups, or disk cleanup. These small, optimized PE files may match the PeCompact signature.
  • Filter/Exclusion: Exclude processes launched by svchost.exe with the service name Schedule (Task Scheduler service) or exclude specific known-good binary paths (e.g., C:\Program Files\BackupTool\cleanup.exe) verified by the asset inventory.

• Development Environment: Visual Studio or JetBrains IDE Build Processes

  • Scenario: Developers using Visual Studio, IntelliJ, or other IDEs compile and link small C/C++ or C# applications. The linker or compiler may produce compacted PE binaries for testing, or the IDE’s internal helper tools (e.g., devenv.exe spawning csc.exe or link.exe) may generate files matching the compact signature.
  • Filter/Exclusion: Exclude processes where the parent image