MemStub64 GH1

Hunt Hypothesis

The MemStub64 GH1 rule detects potential memory-resident malware execution by identifying suspicious memory stubs commonly associated with advanced persistent threats. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify stealthy, persistence-based attacks that evade traditional signature-based detection.

YARA Rule

rule MemStub64_GH1 {
    meta:
        author = "Jaume Martin"
    condition:
        hash.md5(0, filesize) == "2350403a09e6928f0a7ba5d74da58cb9"
}

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: Windows Update or Microsoft Defender scheduled scan
  Description: A legitimate scheduled task runs MemStub64 as part of a system scan or update process.
  Filter/Exclusion: Check for ProcessName containing svchost.exe or WindowsUpdate.exe, or filter by ImageLoaded paths in system directories like C:\Windows\System32.

• Scenario: Administrative tool usage (e.g., Process Explorer, Process Hacker)
  Description: A security administrator uses a tool like Process Explorer or Process Hacker to inspect memory-mapped files or stubs.
  Filter/Exclusion: Filter by ProcessName containing procexp.exe or processhacker.exe, or check for User field indicating a domain admin or security team member.

• Scenario: Scheduled backup or data integrity check
  Description: A backup tool like Veeam, Acronis, or VSS writer may load memory stubs during a backup or integrity check.
  Filter/Exclusion: Check for ProcessName containing Veeam.exe, Acronis.exe, or vssadmin.exe, or filter by ImageLoaded paths in backup tool directories.

• Scenario: System file integrity check (e.g., DISM, SFC)
  Description: A system file check using DISM or SFC /scannow may temporarily load memory stubs during repair operations.
  Filter/Exclusion: Filter by ProcessName containing dism.exe or sfc.exe, or check for CommandLine arguments related to system repair.

• Scenario: Third-party application with memory-mapped files (e.g., SQL Server, Oracle)
  Description: Applications like SQL Server or **