modifiedHACKSTOPv111f

Hunt Hypothesis

This YARA rule targets specific memory patterns associated with the HACKSTOP malware family, indicating the presence of a known threat actor’s tooling within the environment. Proactively hunting for this signature allows the SOC to identify compromised workstations or servers before the malware can establish persistence or execute further post-exploitation actions.

YARA Rule

rule modifiedHACKSTOPv111f
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 52 B4 30 CD 21 52 FA ?? FB 3D [2] EB ?? CD 20 0E 1F B4 09 E8 }

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: Web Application Deployment (Node.js/Python)

  • Context: During a standard CI/CD pipeline deployment, a package-lock.json or requirements.txt file is updated with new dependencies. If the YARA rule modifiedHACKSTOPv111f contains signatures for common library names (e.g., express, lodash, requests) or specific version strings, it may match the text content of these configuration files.
  • Filter/Exclusion: Exclude files with extensions .json, .txt, .yml, or .yaml located in standard project directories (e.g., C:\Projects\, /var/www/html/) from the scan scope, or add a YARA condition to ignore files smaller than a certain threshold (e.g., < 50KB) if the rule targets binary patterns.

• Scenario: Backup Software Metadata Files

  • Context: Enterprise backup solutions like Veeam, Commvault, or Acronis create metadata files (e.g., .vbk, .cat, .xml) that may contain embedded strings or checksums matching the YARA pattern. If the rule looks for specific hex sequences or ASCII strings associated with “HACKSTOP” or similar keywords, these metadata files can trigger false positives.
  • Filter/Exclusion: Exclude files with extensions .vbk, .cat, .bak, .zip, .7z, or .tar.gz from the detection rule. Additionally, exclude paths under common backup directories such as C:\Backup\, D:\VeeamBackup\, or /var/backups/.

• Scenario: Development IDE Caches and Logs

  • Context: Developers using IDEs like Visual Studio, IntelliJ, or VS Code generate cache files (e.g., .vs/, .idea/, `.