CVE-2025-21703: netem: Update sch->q.qlen before qdisc_tree_reduce_backlog()
First published: Tue Feb 18 2025(Updated: )
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.
Credit: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Linux Kernel |
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Reference Links
- https://git.kernel.org/stable/c/1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5
- https://git.kernel.org/stable/c/6312555249082d6d8cc5321ff725df05482d8b83
- https://git.kernel.org/stable/c/839ecc583fa00fab785fde1c85a326743657fd32
- https://git.kernel.org/stable/c/638ba5089324796c2ee49af10427459c2de35f71
- https://git.kernel.org/stable/c/7b79ca9a1de6a428d486ff52fb3d602321c08f55
Frequently Asked Questions
What is the severity of CVE-2025-21703?
CVE-2025-21703 has a moderate severity rating affecting the Linux kernel.
How do I fix CVE-2025-21703?
To fix CVE-2025-21703, update your Linux kernel to the latest stable version that includes the security patch.
Which versions of the Linux kernel are affected by CVE-2025-21703?
CVE-2025-21703 affects specific versions of the Linux kernel prior to the applied security update.
Is CVE-2025-21703 publicly known?
Yes, CVE-2025-21703 is a publicly disclosed vulnerability.
What type of vulnerability is CVE-2025-21703?
CVE-2025-21703 is related to a backlog management issue in the networking subsystem of the Linux kernel.
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