Ransomware Hackers Using AuKill Tool to Disable EDR Software Using BYOVD Attack

Threat actors are employing a previously undocumented "defense evasion tool" dubbed AuKill that's designed to disable endpoint detection and response (EDR) software by means of a Bring Your Own Vulnerable Driver (BYOVD) attack.

"The AuKill tool abuses an outdated version of the driver used by version 16.32 of the Microsoft utility, Process Explorer, to disable EDR processes before deploying either a backdoor or ransomware on the target system," Sophos researcher Andreas Klopsch said in a report published last week.

Incidents analyzed by the cybersecurity firm show the use of AuKill since the start of 2023 to deploy various ransomware strains such as Medusa Locker and LockBit. Six different versions of the malware have been identified to date. The oldest AuKill sample features a November 2022 compilation timestamp.

The BYOVD technique relies on threat actors misusing a legitimate, but out-of-date and exploitable, driver signed by Microsoft (or using a stolen or leaked certificate) to gain elevated privileges and turn off security mechanisms.

By using valid, susceptible drivers, the idea is to bypass a key Windows safeguard known as Driver Signature Enforcement that ensures kernel-mode drivers have been signed by a valid code signing authority before they are allowed to run.

Play ransomware is notable for not only utilizing intermittent encryption to speed up the process, but also for the fact that it's not operated on a ransomware-as-a-service (RaaS) model. Evidence gathered so far points to Balloonfly carrying out the ransomware attacks as well as developing the malware themselves.

Grixba and VSS Copying Tool are the latest in a long list of proprietary tools such as Exmatter, Exbyte, and PowerShell-based scripts that are used by ransomware actors to establish more control over their operations, while also adding extra layers of complexity to persist in compromised environments and evade detection.

Another technique increasingly adopted by financially-motivated groups is the use of the Go programming language to develop cross-platform malware and resist analysis and reverse engineering efforts.

Indeed, a report from Cyble last week documented a new Golang ransomware called CrossLock that employs the double-extortion technique to increase the likelihood of payment from its victims, alongside taking steps to sidestep event tracing for Windows (ETW).

"This functionality can enable the malware to avoid detection by security systems that depend on event logs," Cyble said. "CrossLock Ransomware also performs several actions to reduce the chances of data recovery while simultaneously increasing the attack's effectiveness."

Source: Ransomware Hackers Using AuKill Tool to Disable EDR Software Using BYOVD Attack (thehackernews.com)