CodeCryptv016bv0163b

Hunt Hypothesis

This hypothesis targets the presence of obfuscated or packed code artifacts, which adversaries frequently employ to hide malicious payloads from static analysis tools. Proactively hunting for these patterns in Azure Sentinel allows the SOC to identify stealthy implant or loader stages that may be evading signature-based detections before they execute their full payload.

YARA Rule

rule CodeCryptv016bv0163b
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E9 2E 03 00 00 EB 02 83 3D 58 EB 02 FF 1D 5B EB 02 0F C7 5F }

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 Build Artifacts in CI/CD Pipelines: Automated build agents (e.g., Jenkins, Azure DevOps, or GitHub Actions) often compile C/C++ or Rust code where the compiler or linker applies standard obfuscation or packing techniques (like UPX or custom packers) to reduce binary size. This can result in binaries matching generic code encryption signatures.
  • Filter/Exclusion: Exclude processes running under specific CI/CD service accounts (e.g., jenkins, azure-pipelines, github-actions) or paths within build artifact directories (e.g., C:\Jenkins\workspace\, D:\builds\).
• Commercial Software Updaters and Installers: Many enterprise applications (e.g., Adobe Creative Cloud, JetBrains Toolbox, or Visual Studio Installer) use self-extracting archives or packed installers that employ code encryption to protect intellectual property or ensure integrity during transfer. These executables frequently reside in Program Files or AppData and are executed by standard user or admin accounts.
  • Filter/Exclusion: Exclude known vendor-specific update services (e.g., AdobeUpdateService.exe, JetBrainsUpdater.exe) or paths containing \Update\, \Installer\, or \Setup\ for major software vendors.
• Scheduled Maintenance and Backup Jobs: Enterprise backup solutions (e.g., Veeam, Commvault, or Acronis) or database maintenance scripts may use packed executables or encrypted helper binaries to perform disk operations or data transfer. These are often triggered by Windows Task Scheduler at specific intervals and run under dedicated service accounts.
  • Filter/Exclusion: Exclude processes initiated by the Task Scheduler (TaskScheduler.exe) or known backup service executables (e.g., VeeamBackup.exe, CommvaultClient.exe) when running under specific maintenance service accounts (e.g., `