LameCryptLaZaRus

Hunt Hypothesis

This hunt hypothesis targets adversaries utilizing the LameCryptLaZaRus malware family to detect early-stage encryption activities that may precede ransomware deployment or data exfiltration. Proactively hunting for this signature in Azure Sentinel is essential because its low-severity classification often results in missed alerts, requiring manual investigation to identify subtle lateral movement before a full-scale incident occurs.

YARA Rule

rule LameCryptLaZaRus
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 66 9C BB 00 [2] 00 80 B3 00 10 40 00 90 4B 83 FB FF 75 F3 66 9D 61 B8 [2] 40 00 FF E0 }

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 4 specific false positive scenarios for the LameCryptLaZaRus detection rule in an enterprise environment, including suggested filters and exclusions:

• Scenario: Automated Backup Encryption by Veeam or Commvault

  • Context: Enterprise backup agents (e.g., Veeam Agent for Windows, Commvault) frequently scan and encrypt large volumes of data on disk. These processes often exhibit high I/O patterns and temporary file creation that mimic the behavior of ransomware encryption, triggering the YARA signature.
  • Filter/Exclusion: Add a process exclusion for known backup service executables (e.g., VeeamService.exe, CommServe.exe) running under the system or dedicated backup account context (NT SERVICE\VeeamBackup).

• Scenario: Scheduled Antivirus Scanning with Real-Time Protection

  • Context: During off-hours, scheduled deep scans by security suites like Microsoft Defender for Endpoint or Symantec Endpoint Protection may lock and process files in a manner that resembles the “locking” behavior of LameCryptLaZaRus. The YARA rule might flag the scanning engine’s temporary file handling as suspicious encryption activity.
  • Filter/Exclusion: Exclude processes matching MsMpEng.exe (Microsoft Defender) or Symantec Antivirus Console.exe when they are performing scheduled scans, specifically filtering out alerts where the parent process is a known scheduler service (TaskScheduler.exe).

• Scenario: Document Management and E-Signature Workflows

  • Context: Tools like Adobe Acrobat Pro DC or DocuSign often perform batch processing on PDFs, applying digital signatures and encryption to documents in shared network folders. This involves rapid file modification and metadata updates that can trigger the detection logic designed for ransomware file locking.
  • Filter/Exclusion: Create a rule exclusion based