PrintNightmare created havoc when it was accidentally disclosed by Chinese security researchers who put out a proof-of-concept exploit thinking the vulnerability in Windows Print Spooler had already been patched by Microsoft, which pushed the company to put out a new patch to address the remote code exploitation (RCE) vulnerability as well.
Now, Benjamin Delpy, creator of popular post exploitation tool Mimikatz, has found a way to exploit the vulnerability in the Windows Print Spooler to enable any user to gain admin privileges on a vulnerable computer.
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According to reports, Delpy’s workaround takes advantage of the fact that Windows doesn’t prevent Limited users from installing printer drivers. Furthermore, it won’t complain when these drivers are fetched from remote print servers, and will then run them with the System privilege level.
No end to the abuse
Notably, a section of security researchers, including Delpy, had raised concerns about the patch arguing that it’s how Microsoft checks for remote libraries in the PrintNightmare patch that offers an opportunity to work around the patch.
In a tweet, Delpy mentioned that PrintNightmare has taught him “a lot about printer spooler & drivers (even how to build and sign them).”
He’s put all his learnings into action by demonstrating a proof-of-concept (PoC) that downloads a rogue driver that misuses the latitude it’s given by Windows to eventually fire up a system prompt even for a user with a limited access account.
Speaking to Bleeping Computer, Delpy shared that we haven’t seen the last of Windows print spooler abuse, pointing to a couple of upcoming sessions at DefCon and Black Hat conferences that will share new shortcomings and exploits.