MemStub32 GH1 | SOC Hunt Feed

Hunt Hypothesis

The MemStub32 GH1 rule detects potential memory-resident malware execution by identifying suspicious memory stubs associated with known malicious activity. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage threats that evade traditional signature-based detection.

YARA Rule

rule MemStub32_GH1 {
    meta:
        author = "Jaume Martin"
    condition:
        hash.md5(0, filesize) == "0a579ad25fdd4db8110aac4dbb7d2da3"
}

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
Source Rule

False Positive Guidance

Scenario: Scheduled system maintenance using Task Scheduler to run a legitimate cleanup tool like CCleaner or Disk Cleanup.
Filter/Exclusion: Exclude processes with ImageLoaded containing “ccleaner” or “diskcleanup” in the YARA rule.
Scenario: Administrative task involving Windows Update or Group Policy deployment that temporarily loads memory-resident modules.
Filter/Exclusion: Exclude processes with ImageLoaded containing “wuau” or “gpo” in the YARA rule.
Scenario: Use of Process Explorer or Procmon by IT administrators for troubleshooting or monitoring system behavior.
Filter/Exclusion: Exclude processes with ImageLoaded containing “procexp” or “procmon” in the YARA rule.
Scenario: Execution of PowerShell scripts for routine system configuration or patch management, which may load memory-resident modules.
Filter/Exclusion: Exclude processes with ImageLoaded containing “powershell” and command-line arguments related to patching or configuration.
Scenario: Legitimate use of Windows Defender or Microsoft Defender ATP for real-time protection, which may trigger memory-resident behavior.
Filter/Exclusion: Exclude processes with ImageLoaded containing “mpengine” or “defender” in the YARA rule.