CVE-2025-38350

A use-after-free (UAF) vulnerability was found in the Linux kernel's net/sched subsystem, specifically in the Credit-Based Shaper (CBS) qdisc implementation (sch_cbs). The vulnerability occurs because the CBS qdisc's reset function (qdisc_reset_queue()) only resets its internal queue but fails to reset its child qdisc recursively. As a result, a mismatch in queue length (qlen) occurs between CBS and its children during interface resets, eventually allowing attackers to trigger UAF on a parent HFSC scheduler.

On Red Hat Enterprise Linux 8 and later releases, regular (non-root) users can exploit this issue by abusing unprivileged user namespaces. On Red Hat Enterprise Linux 7, unprivileged user namespaces are disabled by default. Red Hat Enterprise Linux 6 did not include support for them at all, meaning that root privileges are necessary to trigger this flaw.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

To mitigate this issue, prevent the sch_cbs module from being loaded. Please see https://access.redhat.com/solutions/41278 for how information on how to blacklist a kernel module to prevent it from loading automatically.