Malwareusedbycyberthreatactor1

Hunt Hypothesis

This detection identifies the execution of specific malware signatures associated with Cyber Threat Actor 1, indicating potential initial compromise or lateral movement within the environment. Proactive hunting for this indicator in Azure Sentinel is essential to validate early-stage infections and correlate low-severity alerts with broader campaign activities before they escalate into significant incidents.

YARA Rule

rule Malwareusedbycyberthreatactor1
{
	strings:
		// vvv---- this sig hits on a legit CRT function it seems. 
		$heapCreateFunction_0 = {33C06A003944240868001000000F94C050FF15????????85C0A3???????07436E893FEFFFF83F803A3???????0750D68F8030000E8??00000059EB0A83F8027518E8????000085C0750FFF35???????0FF15???????033C0C36A0158C3}
		
		$heapCreateFunction = { 55 8B EC B8 2C 12 00 00 E8 ?? ?? FF FF 8D 85 68 FF FF FF 53 50 C7 85 68 FF FF FF 94 00 00 00 FF 1? ?? ?? ?? ?0 85 C0 74 1A 83 BD 78 FF FF FF 02 75 11 83 BD 6C FF FF FF 05 72 08 6A 01 58 E9 02 01 00 00 8D 85 D4 ED FF F6 89 01 00 00 05 06 8? ?? ?? ?? 0F F1 5? ?? ?? ?? 08 5C 00 F8 4D 00 00 00 03 3D B8 D8 DD 4E DF FF F3 89 DD DF FF F7 41 38 A0 13 C6 17 C0 83 C7 A7 F0 42 C2 08 80 14 13 81 97 5E D8 D8 5D 4E DF FF F6 A1 65 06 8? ?? ?? ?? 0E 8? ?? ?0 00 08 3C 40 C8 5C 07 50 88 D8 5D 4E DF FF FE B4 98 D8 56 4F EF FF F6 80 40 10 00 05 05 3F F1 5? ?? ?? ?? 03 89 D6 4F EF FF F8 D8 D6 4F EF FF F7 41 38 A0 13 C6 17 C0 83 C7 A7 F0 42 C2 08 80 14 13 81 97 5E D8 D8 56 4F EF FF F5 08 D8 5D 4E DF FF F5 0E 8? ?? ?? ?? ?5 95 93 BC 37 43 E6 A2 C5 0E 8? ?? ?? ?? ?5 93 BC 35 97 43 04 08 BC 83 81 87 40 E8 03 93 B7 50 48 81 9E B0 14 13 81 97 5F 26 A0 A5 35 0E 8? ?? ?0 00 08 3C 40 C8 3F 80 27 41 D8 3F 80 37 41 88 3F 80 17 41 38 D4 5F C5 0E 89 8F EF FF F8 07 DF C0 65 91 BC 08 3C 00 35 BC 9C}
		
  	// vvv---- this sig hits on a legit CRT function it seems. 
		$getMajorMinorLinker = {568B7424086A00832600FF15???????06681384D5A75148B483C85C9740D03C18A481A880E8A401B8846015EC3}

		$openServiceManager = {FF15???0?0?08B?885??74????????????????5?FF15???0?0?08B?????0?0?08BF?85F?74}
	
	condition:
	
		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 4 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the Malwareusedbycyberthreatactor1 YARA rule in an enterprise environment, including suggested filters and exclusions:

• Endpoint Protection Scanning and Quarantine Operations

  • Scenario: Enterprise Endpoint Detection and Response (EDR) agents like CrowdStrike Falcon, SentinelOne, or Microsoft Defender for Endpoint frequently scan the system. During a scheduled full-system scan, these tools often extract archived payloads (e.g., .zip or .cab files containing legacy binaries) to analyze them against their local YARA signatures. This extraction process triggers the rule because the extracted binary matches the known malware signature within the archive, even though it is being actively managed by a trusted security tool.
  • Suggested Filter/Exclusion: Exclude processes where the parent executable path contains C:\Program Files\CrowdStrike, C:\ProgramData\SentinelOne, or C:\Windows\System32\MsMpEng.exe. Additionally, add an exclusion for file paths located in the EDR’s temporary quarantine directories (e.g., C:\ProgramData\<Vendor>\Quarantine).

• Software Deployment and Patch Management

  • Scenario: Automated patch management tools such as Microsoft SCCM (Configuration Manager), Ivanti, or Jamf Pro deploy software updates to thousands of endpoints. When these agents install a new application or update an existing one, they often extract installer packages that contain signed binaries matching the Malwareusedbycyberthreatactor1 signature. The rule triggers during the installation phase when the deployment service writes these files to disk before the OS fully registers them as trusted.
  • Suggested Filter/Exclusion: Create a filter to exclude events where the process name is ccmexec.exe, `IvantiAgentService.exe