In a newly detected attack campaign, the attackers behind RobbinHood ransomware deploy legitimate, digitally signed hardware drivers to delete security tools on target machines before they encrypt files.
These attacks exploit known vulnerability CVE-2019-19320, report Sophos researchers who investigated two attacks employing this technique. The flaw exists in a signed driver that is part of a now-deprecated software package published by Taiwanese motherboard manufacturer Gigabyte. When it was patched with proof-of-concept code in 2018, Gigabyte said its products weren't affected by the flaws. While the company later rescinded its statement, it continued using the vulnerable driver, which is still a threat.
The code-signing mechanism used to digitally sign the driver comes from Verisign, which has not revoked the signing certificate, Sophos' Andrew Brandt and Mark Loman write in a blog post on their findings. As a result, the Authenticode signature for the driver remains valid.
The attackers use the Gigabyte driver as a wedge to load a second, unsigned driver onto a Windows machine. This second driver then has the freedom to kill processes and files belonging to security tools and bypass tamper protection so the ransomware can continue to spread. This technique has been used to subvert a setting in kernel memory in Windows 7, 8, and 10.
"The malicious driver contains only code to kill, nothing else," Loman, director of engineering for Sophos, said in an email to Dark Reading. "So even if you have a fully patched Windows computer with no known vulnerabilities, the ransomware provides the attackers with one that lets them destroy your defenses as a precursor to the ransomware ..
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