SEH vba

Hunt Hypothesis

The SEH vba rule detects potential adversarial use of Visual Basic for Applications (VBA) code embedded within a document to exploit Structured Exception Handling (SEH) vulnerabilities, which could lead to arbitrary code execution. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage attacks that leverage document-based exploitation vectors.

YARA Rule

rule SEH__vba : AntiDebug SEH {
	meta:
		weight = 1
		Author = "naxonez"
		reference = "https://github.com/naxonez/yaraRules/blob/master/AntiDebugging.yara"
	strings:
		$ = "vbaExceptHandler"
	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

References

• https://github.com/naxonez/yaraRules/blob/master/AntiDebugging.yara
• Source Rule

False Positive Guidance

• Scenario: A legitimate VBA macro used in Microsoft Excel for automating data processing tasks.
  Filter/Exclusion: Exclude files with the .xls or .xlsx extension that are located in standard office document directories (e.g., C:\Users\*\Documents\ or C:\Program Files\Microsoft Office\).
  Additional Context: Use a filter to exclude files that contain the string Microsoft Excel or Excel in their content.

• Scenario: A scheduled system maintenance task that uses a VBA script to clean temporary files.
  Filter/Exclusion: Exclude files with the .vbs or .vba extension that are located in the Windows Task Scheduler job directory (e.g., C:\Windows\Tasks\).
  Additional Context: Use a filter to check for the presence of Task Scheduler or schtasks.exe in the process tree.

• Scenario: A legitimate admin task involving the use of VBA for automating report generation in Microsoft Access.
  Filter/Exclusion: Exclude files with the .accdb or .mdb extension that are located in the Microsoft Access application directory (e.g., C:\Program Files\Microsoft Office\Access).
  Additional Context: Use a filter to check for the presence of Microsoft Access or msaccess.exe in the process tree.

• Scenario: A user-generated script in a shared enterprise VBA library used across multiple departments.
  Filter/Exclusion: Exclude files that are located in a shared network drive or a known enterprise VBA library path (e.g., \\server\shared_vba_lib\).
  Additional Context: Use a filter to check for the presence of a known enterprise VBA library identifier or version string.

• Scenario: A legitimate PowerShell script that uses COM automation to interact with Excel and execute VBA code