“A local, authenticated attacker could gain elevated local system or administrator privileges through a vulnerability in the Win32k.sys driver.” reads the advisory published by Microsoft.
Now RyeLv published a detailed analysis of the vulnerability that affects all supported support versions of Windows 10.
Using this vulnerability, threat actors with limited access to a compromised device can easily elevate their privileges to help spread laterally within the network, create new administrative users, or perform privileged commands.
“Attacker can intercept this callback [xxxClientAllocWindowClassExtraBytes] through hook xxxClientAllocWindowClassExtraBytes in KernelCallbackTable,and use the NtUserConsoleControl method to set the ConsoleWindow flag of the tagWND object, which will modify the window type.” reads the analysis published by RyeLv. “After the final callback, the system does not check whether the window type has changed, and the wrong data is referenced due to type confusion. The difference before and after the flag modified is that before setting the flag, the system thinks that tagWND.WndExtra saves a user_mode pointer; after the flag is set, the system thinks that tagWND.WndExtra is the offset of the kernel desktop heap,and attacker can control this offset, then cause out-of-bounds R&W.”
Multiple experts confirmed that the exploits correctly work, including the CERT/CC vulnerability analyst Will Dormann:
Administrators that have yet to install January 2022 security updates are recommended to do it as soon as possible to prevent attacks exploiting this issue.
(SecurityAffairs – hacking, REvil ransomware)