yodasCrypter13AshkbizDanehkar

Hunt Hypothesis

This detection identifies potential fileless or memory-based encryption activities associated with the specific YODAS crypter signature, which may indicate early-stage ransomware or data exfiltration attempts. Proactively hunting for this behavior in Azure Sentinel allows the SOC team to validate low-severity alerts that could precede a larger incident, ensuring timely intervention before encryption spreads across critical assets.

YARA Rule

rule yodasCrypter13AshkbizDanehkar
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 53 56 57 60 E8 00 00 00 00 5D 81 ED 6C 28 40 00 B9 5D 34 40 00 81 E9 C6 28 40 00 8B D5 81 C2 C6 28 40 00 8D 3A 8B F7 33 C0 EB 04 90 EB 01 C2 AC }

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 yodasCrypter13AshkbizDanehkar detection rule, including recommended filters and exclusions:

• Scenario: Automated Backup Encryption by Veeam or Commvault

  • Context: Enterprise backup agents (e.g., Veeam.Backup.Service.exe or commvault.cmd) frequently encrypt large data blocks during scheduled nightly windows. The YARA rule may flag the encryption engine’s memory footprint and file I/O patterns as suspicious “crypter” behavior, mistaking legitimate backup encryption for ransomware activity.
  • Filter/Exclusion: Create a whitelist exclusion based on the specific process image path (e.g., C:\Program Files\Veeam\BackupAndReplication\...) and restrict detection to non-business hours if the rule triggers during known maintenance windows.

• Scenario: Microsoft Office 365 ProPlus Document Protection

  • Context: When users open or save sensitive documents with “Encrypt with Password” enabled, WINWORD.EXE or EXCEL.EXE utilizes internal cryptographic APIs that match the YARA signature for file encryption. This is common in legal and finance departments where document protection is standard operating procedure.
  • Filter/Exclusion: Exclude processes belonging to the Microsoft Office suite (*Office16*\WINWORD.EXE, *Office16*\EXCEL.EXE) from this rule, or add a filter that ignores events where the parent process is OFFICESETUP.EXE during installation phases.

• Scenario: Antivirus Real-Time Scanning and Heuristic Analysis

  • Context: Endpoint Protection platforms like CrowdStrike Falcon or Microsoft Defender for Endpoint perform real-time scanning which involves temporary file creation, hashing, and encryption of scan logs. The YARA rule might interpret the rapid I/O and memory