Silver Fox Exploits Microsoft-Signed WatchDog Driver to Deploy ValleyRAT Malware
Sep 02, 2025
Financial Fraud / Endpoint Protection
The threat actor known as Silver Fox has been attributed to abuse of a previously unknown vulnerable driver associated with WatchDog Anti-malware as part of a Bring Your Own Vulnerable Driver ( BYOVD ) attack aimed at disarming security solutions installed on compromised hosts. The vulnerable driver in question is "amsdk.sys" (version 1.0.600), a 64-bit, validly signed Windows kernel device driver that's assessed to be built upon Zemana Anti-Malware SDK. "This driver, built on the Zemana Anti-Malware SDK, was Microsoft-signed, not listed in the Microsoft Vulnerable Driver Blocklist , and not detected by community projects like LOLDrivers," Check Point said in an analysis. The attack is characterized by a dual-driver strategy, where a known vulnerable Zemana driver ("zam.exe") is used for Windows 7 machines, and the undetected WatchDog driver for systems that run on Windows 10 or 11. The WatchDog Anti-malware driver has been found to contain mu...