133. Marbled Dust: What to Hunt for?

Hello everyone!

Today we'll discuss a fresh report by Microsoft Threat Intelligence on Marbled Dust. The adversary exploited a zero-day vulnerability in Output Messenger Server Manager (CVE-2025-27920).

This directory traversal vulnerability enabled the threat actors to upload malicious files into the server’s startup directory. For example, the adversary dropped the malicious files OM.vbs and OMServerService.vbs to the Output Messenger server startup folder and dropped the malicious file OMServerService.exe to the server’s C:\Users\public\videos directory.

First, we can hunt for suspicious .vbs files executed from the startup folder:

event_type: "processcreatewin"

AND

cmdline: ("startup" AND "vbs")

Second, we can hunt for suspicious files executed from C:\Users\public\videos:

event_type: "processcreatewin"

AND

proc_file_path: "users\\public\\videos"

See you tomorrow!

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