CVE-2021-24088

Windows Local Spooler Remote Code Execution Vulnerability

Recent assessments:

bwatters-r7 at August 10, 2021 9:35pm UTC reported:

This entry is based off the blackhat talk by Zhiniang Peng, Xuefeng Li, and Lewis Lee on August 4, 2021.

They said CVE-2021-24088, 24077, and 1722 were all similar, but only described 24088.
For 24088, there’s a bug in EnumJobsInLocalQueue where the user submits a buffer and job size. Because the buffer used in this case has metadata written to the top of the buffer and strings written to the bottom of the buffer, the buffer functionally grows toward the middle (AKA itself). There bug is in the check to ensure proper size of the buffer so that it does not cause an overwrite of the string data to the metadata, but that check is vulnerable to an integer overflow (I am not sure of the exact cause). Because the check can be bypassed using the integer overflow, it means someone can arbitrarily write data in the form of a string to the meta data section, or even underflow the address and write arbitrary data to adjacent heap allocations.
Because the nature of the exploit, being able to write arbitrary data to the heap could result in code execution, but as I have not seen a PoC that goes through all the steps, I’m unable to say definitively how easy the exploit is to create or run or what the attacker value is. Mitigations are as always, patch, and/or disable the spooler service on devices that do not need it.

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