Malwareusedbycyberthreatactor2

Hunt Hypothesis

This hunt targets adversary behavior characterized by the execution of specific malware signatures identified by the “Malwareusedbycyberthreatactor2” YARA rule, which may indicate early-stage infection or lateral movement attempts. Proactively hunting for these indicators in Azure Sentinel is critical to validate low-severity alerts and detect potential dwell time before adversaries escalate their activities within the cloud environment.

YARA Rule

rule Malwareusedbycyberthreatactor2
{
	strings:
		$str1 = "_quit"
		$str2 = "_exe"
		$str3 = "_put"
		$str4 = "_got"
		$str5 = "_get"
		$str6 ="_del"
		$str7 = "_dir"
		$str8 = { C7 44 24 18 1F F7}
	
	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 8 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the Malwareusedbycyberthreatactor2 detection rule in an enterprise environment, along with suggested filters or exclusions:

• Endpoint Protection Scanning and Quarantine Operations

  • Scenario: The YARA rule matches a known legitimate file hash or signature that is frequently scanned by the organization’s Endpoint Detection and Response (EDR) solution. For instance, when CrowdStrike Falcon or Microsoft Defender for Endpoint performs an on-demand full system scan, it may load specific DLLs or executables into memory that share structural similarities with the threat actor’s malware family, triggering a match even though no malicious activity is occurring.
  • Filter/Exclusion: Create an exclusion based on process lineage. Exclude alerts where the parent process is C:\Program Files\CrowdStrike\fsagent.exe or C:\ProgramData\MsMpEng\AntimalwareService.exe. Additionally, whitelist known benign file hashes identified during a baseline scan of these EDR components.

• Software Deployment via Configuration Management Tools

  • Scenario: During scheduled patching windows, configuration management tools like Ansible, Chef, or Microsoft SCCM (Configuration Manager) deploy updates to critical servers. The deployment agent often extracts temporary installer packages (e.g., .msi or .exe) into the C:\Windows\Temp directory. If the malware rule detects specific strings or code blocks common in these installers, it may flag them as suspicious activity by a threat actor, mistaking the deployment artifact for an initial infection vector.
  • Filter/Exclusion: Implement a path-based exclusion for temporary directories used by deployment tools (e.g., C:\Windows\Temp\*, C:\ProgramData\SCCM\*). Furthermore, exclude alerts where the process name matches known deployment agents such