The BlackByte ransomware has been observed targeting a vulnerability in a legitimate driver to disable endpoint detection and response (EDR) solutions running on the victim machine.
Although a decryptor for BlackByte ransomware was released in October last year, the threat has continued to remain active, with the FBI warning of attacks targeting critical infrastructure sectors, including government, financial, and food and agriculture organizations.
While investigating recent activity surrounding the ransomware-as-a-service (RaaS) and its new data leak site, Sophos security researchers discovered that the threat has been using a sophisticated technique that allows it to bypass security products.
Called ‘Bring Your Own Driver’, the technique involves dropping a vulnerable driver version on the victim’s machine, executing it, and abusing it to remove process creation callbacks from the kernel memory.
For this, BlackByte ransomware abuses drivers that Micro-Star’s graphics card overclocking utility MSI AfterBurner 220.127.116.1158 uses to gain extended control over graphic cards on the system. The ransomware operators also use valid code signing certificates to sign those drivers.
The RTCore64.sys driver, Sophos explains, is affected by an authenticated read/write arbitrary memory vulnerability. Tracked as CVE-2019-16098, the issue leads to privilege escalation, information disclosure, and code execution with elevated privileges.
The technique works because “the I/O control codes in RTCore64.sys are directly accessible by user-mode processes” and because the targeted vulnerability can be exploited by simply accessing these control codes, without the need for exploit code.
BlackByte ransomware exploits the vulnerable driver to remove callback entries of drivers used by EDR products from kernel memory, by overwriting them with zeros.
“The evasion technique supports disabling a whopping list of over 1,000 drivers on which security products rely to provide protection,” Sophos notes.
Other ransomware families out there were also seen using this technique in attacks this year, albeit they abuse different drivers, including the mhyprot2.sys anti-cheat driver for the Genshin Impact video game and the aswarpot.sys Avast anti-rootkit driver, which was being abused by AvosLocker ransomware.