MSLRHv032afakeyodascryptor12emadicius

Hunt Hypothesis

This hypothesis targets the presence of the “afakeyodascryptor” YARA signature, which likely indicates a specific low-severity cryptor or obfuscated payload used for initial access or in-memory execution. Proactively hunting for this pattern in Azure Sentinel allows the SOC team to identify dormant or stealthy malware instances that may evade standard behavioral detections, ensuring early visibility into potential low-fidelity threats within the environment.

YARA Rule

rule MSLRHv032afakeyodascryptor12emadicius
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 00 00 00 00 5D 81 ED F3 1D 40 00 B9 7B 09 00 00 8D BD 3B 1E 40 00 8B F7 AC 90 2C 8A C0 C0 78 90 04 62 EB 01 00 61 EB 05 E8 EB 04 40 00 EB FA E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF 83 C4 08 74 04 75 02 EB 02 EB 01 81 50 E8 02 00 00 00 29 5A 58 6B C0 03 E8 02 00 00 00 29 5A 83 C4 04 58 74 04 75 02 EB 02 EB 01 81 0F 31 50 0F 31 E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF }

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 Scenario: A DevOps team executes a custom Python-based encryption utility (e.g., aes_encryptor.py) to rotate secrets for a microservice deployment. The script uses a hardcoded key string or specific cryptographic library imports (like pycryptodome) that match the YARA pattern for “cryptor” behavior, triggering the rule during the CI/CD pipeline.

  • Filter/Exclusion: Exclude processes where the parent process is a CI/CD agent (e.g., jenkins.exe, azureagent.exe, github-runner.exe) or where the command line contains specific arguments like --rotate-keys or --deploy.

• Legitimate Scenario: An IT administrator runs a scheduled PowerShell job to encrypt backup files using System.IO.FileStream with AES-256 before uploading them to Azure Blob Storage. The YARA rule detects the memory pattern of the encryption routine or the specific string literals used in the PowerShell script, flagging it as a potential cryptor.

  • Filter/Exclusion: Exclude events where the process name is powershell.exe or pwsh.exe and the command line contains Encrypt or Backup keywords, or restrict the rule to exclude paths under C:\Scripts\Backup\ or C:\AdminTools\.

• Legitimate Scenario: A security engineer performs a manual penetration test using a tool like Cobalt Strike or Mimikatz in a controlled test environment. The tool’s memory footprint or embedded strings match the YARA signature for “afakeyodascryptor” (a likely obfuscated or generic cryptor pattern), causing a false positive in the production SOC feed if the test environment is not properly tagged.

  • Filter/Exclusion: Exclude hosts tagged with Environment=Test or Tag=PenTest in the asset inventory