Silver Fox Exploits Microsoft-Signed WatchDog Driver to Distribute ValleyRAT Malware
Date: September 2, 2025
Categories: Financial Fraud / Endpoint Protection
The threat actor known as Silver Fox has been linked to the exploitation of a previously undetected vulnerable driver associated with WatchDog Anti-malware. This attack, classified as a Bring Your Own Vulnerable Driver (BYOVD) incident, aims to neutralize security solutions on compromised systems.
The specific driver involved, “amsdk.sys” (version 1.0.600), is a 64-bit, validly signed Windows kernel device driver believed to be based on the Zemana Anti-Malware SDK. According to an analysis by Check Point, “This driver, created using the Zemana Anti-Malware SDK, was Microsoft-signed, not included in the Microsoft Vulnerable Driver Blocklist, and evaded detection by community initiatives such as LOLDrivers.”
The attack employs a dual-driver approach, utilizing a known vulnerable Zemana driver (“zam.exe”) for Windows 7 systems, while leveraging the undetected WatchDog driver for Windows 10 and 11 environments. The WatchDog Anti-malware driver has been identified as containing multiple vulnerabilities.