CodeCryptv014b

Hunt Hypothesis

This detection identifies potential code obfuscation or encryption activities within executable files that may indicate an adversary attempting to evade static analysis by hiding malicious logic. Proactively hunting for this behavior in Azure Sentinel is essential to uncover stealthy threats that might bypass traditional signature-based defenses, allowing the SOC team to investigate suspicious binaries before they execute harmful payloads.

YARA Rule

rule CodeCryptv014b
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E9 C5 02 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

Here are 5 specific false positive scenarios for the CodeCryptv014b detection rule, along with recommended filters and exclusions:

• Antivirus Real-Time Scanning of Encrypted Archives

  • Scenario: The enterprise endpoint protection suite (e.g., Microsoft Defender Antivirus or CrowdStrike Falcon) performs real-time scanning on large .7z or encrypted .zip archives stored in shared network drives. The YARA rule flags the internal encryption headers and compression streams as suspicious code obfuscation, triggering an alert when users simply open these files.
  • Filter/Exclusion: Add a process exclusion for MsMpEng.exe (Defender) or C-Host.exe (CrowdStrike) to ignore alerts generated while scanning file paths containing \Shared\Archives\. Alternatively, exclude the specific file extensions .7z, .rar, and encrypted .zip from the rule’s scope.

• Scheduled Backup Job Execution

  • Scenario: A nightly automated backup job running via Windows Task Scheduler utilizes Veeam Agent for Windows or Acronis Cyber Protect. During the backup window, the agent encrypts and compresses database logs before transmission. The rule detects the high entropy of these encrypted payloads as potential code packing/obfuscation typical of malware.
  • Filter/Exclusion: Create a time-based exclusion for the alert during the defined maintenance window (e.g., 02:00–04:00 UTC). Additionally, exclude processes named VeeamAgent.exe or AcronisCyberProtectService.exe from triggering this rule.

• CI/CD Pipeline Artifact Generation

  • Scenario: In the DevOps environment, the Jenkins build server executes a pipeline step using Docker Buildx to create