device driver

Attackers have been using the ThrottleStop.sys driver to disable antivirus software in compromised networks since October 2024. This driver, designed for CPU throttling, allows malware to gain kernel-level memory access and terminate security processes. Initial access is typically gained through stolen RDP credentials or brute-forced administrative accounts, enabling the deployment of the AV killer alongside ransomware like MedusaLocker. Once inside, attackers extract additional user credentials using tools like Mimikatz and move laterally with Pass-the-Hash techniques. They upload two key components, ThrottleBlood.sys (the renamed driver) and All.exe (the AV killer), to user directories. The malware effectively disables Windows Defender and other endpoint protections, leading to severe data encryption in industries with exposed RDP endpoints, particularly affecting victims in Brazil, Ukraine, Kazakhstan, Belarus, and Russia. Securelist analysts noted that traditional self-defense features in Kaspersky products can counter this AV killer, but many organizations still rely on less effective solutions. The malware exploits two vulnerable IOCTL functions in the ThrottleStop.sys driver, allowing arbitrary memory reads and writes. It uses a loop to match and terminate antivirus processes by invoking kernel functions. The malware avoids detection by restoring original kernel bytes after execution. This situation highlights the need for improved driver integrity monitoring and robust security strategies.