CVE-2022-21999

Windows Print Spooler Elevation of Privilege Vulnerability

Recent assessments:

space-r7 at March 11, 2022 9:07pm UTC reported:

This is a useful vulnerability; however, an existing session on the target is required, and escalation of privileges can sometimes depend on luck. To achieve the directory creation and ultimately the file write, one first needs to reinitialize the print spooler. There exists one primitive to do this using SetPrinterDataEx() and AppVTerminator.dll as a Point and Print dll, but it’s limited to two uses because the print spooler will not automatically restart after two crashes. If the print spooler has reached its maximum number of restarts, then this exploit will only work by restarting the system completely, which is not particularly stealthy. Additionally, the previously-mentioned primitive is limited, as Windows 7 does not appear to have the AppVTerminator dll.

Assuming that the attacker has a printer handle with the PRINTER_ACCESS_ADMINISTER privilege and the ability to restart the print spooler, this vulnerability is fairly easy to exploit. Create a temp directory, set the SpoolDirectory to the temp path with the version 4 directory appended (in UNC path form), create junction between the temp path and the printer driver directory, restart spooler, write malicious dll, then load the dll.

I wouldn’t call this the first priority in the list of vulnerabilities to patch mainly due to an existing session being a requirement and success potentially depending on a reboot, but it should certainly be patched.

Assessed Attacker Value: 3
Assessed Attacker Value: 3Assessed Attacker Value: 4