CVE-2025-21703

In the Linux kernel, the following vulnerability has been resolved: netem: Update sch->q.qlen before qdisc_tree_reduce_backlog() qdisc_tree_reduce_backlog() notifies parent qdisc only if child qdisc becomes empty, therefore we need to reduce the backlog of the child qdisc before calling it. Otherwise it would miss the opportunity to call cops->qlen_notify(), in the case of DRR, it resulted in UAF since DRR uses ->qlen_notify() to maintain its active list.

Jann Horn discovered that the watch_queue event notification subsystem in the Linux kernel contained an out-of-bounds write vulnerability. A local attacker could use this to cause a denial of service or escalate their privileges. Several security issues were discovered in the Linux kernel. An attacker could possibly use these to compromise the system.