RCryptorv13v14Vaska

Hunt Hypothesis

This rule detects the presence of RCryptor ransomware variants (versions 13 and 14) and the Vaska ransomware family, indicating a potential active encryption or staging phase within the environment. Proactively hunting for these specific signatures in Azure Sentinel allows the SOC team to identify compromised hosts or lateral movement artifacts early, mitigating the risk of widespread data encryption before the ransomware completes its execution cycle.

YARA Rule

rule RCryptorv13v14Vaska
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 8B 44 24 04 83 E8 4F 68 [4] FF D0 58 59 50 }
	$a1 = { 55 8B EC 8B 44 24 04 83 E8 4F 68 [4] FF D0 58 59 50 B8 [4] 3D [4] 74 06 80 30 ?? 40 EB F3 }

condition:
		$a0 at pe.entry_point or $a1 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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Legacy Backup Agent Updates: The RCryptor family is frequently used in older or niche backup software (e.g., certain versions of Acronis True Image or Veeam Backup & Replication agents) to encrypt backup archives. When these agents perform scheduled encryption tasks or update their encryption modules, the binary or temporary files may match the YARA signature.

  • Filter/Exclusion: Exclude processes or files located in specific backup agent directories (e.g., C:\Program Files\Acronis\, C:\Program Files\Veeam\) or exclude parent processes like acronis.exe or veeam.exe if the detection is triggered on the child encryption utility.

• Third-Party Disk Encryption Tools: Enterprise environments often deploy third-party full-disk encryption (FDE) or volume encryption tools (e.g., BitLocker management utilities, Symantec PGP, or GPG4Win wrappers) that utilize custom encryption routines. If a vendor updates their encryption library to a version compatible with the RCryptor algorithm (v13/v14), the associated executable or DLL may trigger the rule.

  • Filter/Exclusion: Exclude files with known vendor signatures (e.g., Symantec, GPG) or specific file paths associated with encryption management consoles (e.g., C:\Program Files\Symantec\PGP\).

• Custom Application Packaging: Developers or IT teams may package internal line-of-business (LOB) applications using obfuscation or encryption tools that incorporate RCryptor libraries for code protection or data-at-rest encryption. This is common in Java-based enterprise apps or .NET frameworks where native encryption modules are bundled.

  • Filter/Exclusion: Exclude processes launched by known application servers (e.g., java.exe,