Malware Updater

Hunt Hypothesis

The Malware Updater rule detects potential adversary behavior involving the deployment of malware through periodic or scheduled update mechanisms. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate persistent malware infections that may evade traditional detection methods.

YARA Rule

rule Malware_Updater
{
meta:
	Author="US-CERT Code Analysis Team"
	Date="2017/08/02"
	Incident="10132963"
	MD5_1="8F4FC2E10B6EC15A01E0AF24529040DD"
	MD5_2="584AC94142F0B7C0DF3D0ADDE6E661ED"
	Info="Malware may be used to update multiple systems with secondary payloads"
	super_rule=1
	report = "https://www.us-cert.gov/sites/default/files/publications/MAR-10132963.pdf"
	report = "https://www.us-cert.gov/HIDDEN-COBRA-North-Korean-Malicious-Cyber-Activity"
strings:
	$s0 = { 8A4C040480F15D80C171884C04044083F8107CEC }
	$s1 = { 8A4D0080F19580E97C884D00454B75F0 }
condition: 
	any 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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: Scheduled System Update via Windows Server Update Services (WSUS)
  Description: A legitimate system update process using WSUS may trigger the Malware_Updater YARA rule due to similar file patterns.
  Filter/Exclusion: Check for file.path containing C:\Windows\SoftwareDistribution\ or wsusoffline in the file name.

• Scenario: Microsoft Endpoint Configuration Manager (MECM) Software Deployment
  Description: MECM often deploys software updates and may use similar update mechanisms that could match the Malware_Updater rule.
  Filter/Exclusion: Filter by process.name containing msiexec.exe or ConfigurationManager.exe, or check for process.parent related to MECM services.

• Scenario: Admin Task - Windows Update Agent (WUA) Background Task
  Description: The Windows Update Agent may run background tasks that could be flagged by the Malware_Updater rule.
  Filter/Exclusion: Use process.name matching wuauclt.exe or check for process.parent with svchost.exe and Windows Update service.

• Scenario: Third-Party Patch Management Tool (e.g., SCCM, Altiris)
  Description: Patch management tools often deploy updates and may have similar file structures or behaviors that could trigger the rule.
  Filter/Exclusion: Filter by file.path containing C:\Program Files\Altiris\ or C:\Windows\System32\ccm\ for SCCM.

• Scenario: Legitimate Software Installer with Similar Signature (e.g., Adobe Updater)
  Description: Some legitimate software installers, such as Adobe Updater, may have file signatures that resemble malware update patterns.
  Filter/Exclusion: Check for file.name containing `AdobeUpdater