CVE-2023-4921: Use-after-free in Linux kernel's net/sched: sch_qfq component

Vulnerability summary

CVE-2023-4921 is a high (CVSS 7.8) Use After Free vulnerability in debian debian_linux. EPSS estimates a 0.42% chance of exploitation in the next 30 days, higher than 36.3% of scored vulnerabilities. 2 public exploits are recorded.

Timeline

1. 12-09-2023
   PublishedVulnerability first disclosed.
2. 14-10-2026
   Last modifiedVulnerability information updated.

Description

A use-after-free vulnerability in the Linux kernel's net/sched: sch_qfq component can be exploited to achieve local privilege escalation. When the plug qdisc is used as a class of the qfq qdisc, sending network packets triggers use-after-free in qfq_dequeue() due to the incorrect .peek handler of sch_plug and lack of error checking in agg_dequeue(). We recommend upgrading past commit 8fc134fee27f2263988ae38920bc03da416b03d8.

• CWE-416Use After FreeThe product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.