CVE-2025-21703: netem: Update sch->q.qlen before qdisc_tree_reduce_backlog()
In the Linux kernel, the following vulnerability has been resolved:
netem: Update sch->q.qlen before qdisctreereducebacklog()
qdisctreereducebacklog() 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->qlennotify(), in the case of DRR, it resulted in UAF since DRR uses ->qlennotify() to maintain its active list.
Other sources
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— Launchpad
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
debian/linuxto a version that resolves this vulnerability.Fixed in 5.10.234-1Fixed in 6.1.129-1Fixed in 6.1.135-1Fixed in 6.12.27-1 - Upgrade
Upgrade
debian/linux-6.1to a version that resolves this vulnerability.Fixed in 6.1.129-1~deb11u1
Event History
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.