LameCryptv10

Hunt Hypothesis

This rule targets the LameCrypt v10 ransomware variant, a low-severity threat that encrypts files to disrupt operations and potentially exfiltrate data before encryption. Proactively hunting for this signature in Azure Sentinel allows the SOC to identify early-stage infections or dormant payloads on endpoints, enabling rapid containment before the ransomware can propagate or execute its final encryption routine.

YARA Rule

rule LameCryptv10
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 66 9C BB [4] 80 B3 00 10 40 00 90 4B 83 FB FF 75 F3 66 9D 61 }

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

• Legacy Application Deployment via Group Policy: When IT administrators deploy legacy line-of-business applications (e.g., older versions of SAP GUI, Oracle Client, or specific banking terminals) that bundle outdated cryptographic libraries or use custom, non-standard encryption implementations for local data storage.
  • Filter/Exclusion: Exclude files located in known application directories (e.g., C:\Program Files\LegacyApp\, C:\Program Files (x86)\SAP\) or match against specific known-good hashes of the deployed binaries.
• Development and Testing Environments: Developers using local IDEs or build tools that generate temporary encrypted artifacts or test data files during unit testing, particularly when using custom encryption wrappers or third-party libraries that have not yet been updated to modern standards.
  • Filter/Exclusion: Exclude paths under development directories (e.g., C:\Users\<dev_user>\workspace\, C:\temp\build_artifacts\) or restrict the rule to production servers only by excluding hosts tagged with env=dev or env=test in your CMDB/EDR.
• Scheduled Backup or Archiving Jobs: Enterprise backup agents (e.g., Veeam, Commvault, or custom PowerShell scripts) that perform local pre-encryption of data blocks before sending them to the backup repository, potentially using a proprietary or older encryption algorithm that matches the “LameCrypt” signature.
  • Filter/Exclusion: Exclude processes associated with backup services (e.g., VeeamBackup.exe, commvault_agent.exe) or files with specific extensions (.vbk, .bkp, .enc) located in backup staging directories (e.g., C:\BackupStaging\).
• Third-Party Plugin or Add-on Installation: Installation of third-party plugins for enterprise software (e.g., Jira, Confluence, or custom middleware