Malwareusedbycyberthreatactor3

Hunt Hypothesis

This hunt targets adversary behavior characterized by the execution of specific malware signatures identified by the “Malwareusedbycyberthreatactor3” YARA rule, which may indicate early-stage infection or lateral movement attempts. Proactively hunting for this low-severity indicator in Azure Sentinel is critical to validate its prevalence across endpoints and ensure that potential threats are not overlooked due to their initial low risk classification before they escalate into significant incidents.

YARA Rule

rule Malwareusedbycyberthreatactor3
{
	strings:
		$STR1 = { 50 68 80 00 00 00 68 FF FF 00 00 51 C7 44 24 1C 3a 8b 00 00 }
	
	condition:
		(uint16(0) == 0x5A4D or uint16(0) == 0xCFD0 or uint16(0) == 0xC3D4 or uint32(0) == 0x46445025 or uint32(1) == 0x6674725C) and all of them
}

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 Malwareusedbycyberthreatactor3 YARA rule in an enterprise environment, along with suggested filters or exclusions:

• Scenario: Endpoint Protection Scanning and Quarantine Operations

  • Context: The rule may trigger on legitimate files being processed by the organization’s primary endpoint protection suite (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint, or SentinelOne) during routine background scans. These engines often create temporary copies, quarantine archives, or signature update packages that contain code structures matching the YARA pattern of known threat actor malware families.
  • Suggested Filter: Exclude file paths containing standard antivirus installation directories and quarantine folders (e.g., C:\ProgramData\McAfee\Agent\, C:\Windows\System32\com\CrowdStrike\, or files with extensions like .qar or .tmp located within the AV vendor’s root directory).

• Scenario: Scheduled Software Deployment via Configuration Management Tools

  • Context: Automated patch management and software deployment tools (such as Microsoft SCCM/MECM, Ansible, or Ivanti Endpoint Manager) frequently extract installer packages, scripts, or compressed binaries to temporary execution folders. If the YARA rule detects specific cryptographic signatures or code sections common in these deployment artifacts (e.g., a PowerShell script wrapper used for patching), it may flag them as malicious activity associated with the threat actor.
  • Suggested Filter: Create an exclusion based on the process name of the deployment agent (e.g., ccmexec.exe, AnsibleService.exe) and restrict alerts to files located in temporary deployment paths like %TEMP%\SCCM\ or C:\Program Files\Ivanti\Deployment.

• Scenario: Enterprise Application Updates via Web Browsers