PECompact2xxBitSumTechnologies

Hunt Hypothesis

This detection identifies potentially obfuscated or packed executables utilizing BitSum Technologies’ compression signatures, which adversaries often employ to evade static analysis and conceal malicious payloads within legitimate-looking binaries. Proactively hunting for these artifacts in Azure Sentinel is critical because low-severity alerts may mask sophisticated evasion tactics where attackers leverage packing techniques to bypass traditional signature-based defenses and establish a foothold before executing their primary attack logic.

YARA Rule

rule PECompact2xxBitSumTechnologies
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B8 [4] 50 64 FF 35 00 00 00 00 64 89 25 00 00 00 00 33 C0 89 08 50 45 43 6F 6D 70 61 63 74 32 00 }

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

Here are 3-5 specific false positive scenarios for the PECompact2xxBitSumTechnologies detection rule, including suggested filters and exclusions:

• Scenario: Deployment of Microsoft Office Click-to-Run updates via the OfficeC2RClient.exe process.

  • Context: The Office update client frequently generates compacted PE binaries (often 32-bit or mixed) during background patching cycles, which can match the signature for BitSum Technologies’ compression techniques even though they are native Microsoft artifacts.
  • Filter/Exclusion: Add a whitelist exclusion for the process image path C:\Program Files\Microsoft Office\root\Office16\OfficeC2RClient.exe and its child processes when the file hash matches known Microsoft update signatures.

• Scenario: Execution of scheduled antivirus definition updates by CrowdStrike Falcon or Symantec Endpoint Protection.

  • Context: Security agents often download and unpack compacted definition packages (PE files) that utilize similar bit-summing compression algorithms to reduce memory footprint during real-time scanning, triggering the rule when the agent writes these temporary files to disk.
  • Filter/Exclusion: Exclude file paths containing \ProgramData\Symantec or \Program Files\CrowdStrike\Falcon where the parent process is ccSvcHst.exe (Symantec) or FalconSensorService.exe (CrowdStrike).

• Scenario: Automated software installation via SCCM/Intune using the msiexec.exe wrapper.

  • Context: When System Center Configuration Manager (SCCM) or Microsoft Intune pushes application updates, it often extracts compacted installer packages that utilize 2xx-bit summing logic for payload verification before handing them off to the Windows Installer service.
  • Filter/Exclusion: Create a rule exception where the parent process is