UBUNTU-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.
02 / AFFECTED SOFTWARE
Affected packages
11 explicit affected versions
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37 explicit affected versions
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38 explicit affected versions
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11 explicit affected versions
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14 explicit affected versions
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78 explicit affected versions
11 explicit affected versions
1 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
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.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/638ba5089324796c2ee49af10427459c2de35f71
- https://git.kernel.org/stable/c/1f8e3f4a4b8b90ad274dfbc66fc7d55cb582f4d5
- https://git.kernel.org/stable/c/6312555249082d6d8cc5321ff725df05482d8b83
- https://git.kernel.org/stable/c/638ba5089324796c2ee49af10427459c2de35f71
- https://git.kernel.org/stable/c/839ecc583fa00fab785fde1c85a326743657fd32
- https://ubuntu.com/security/CVE-2025-21703
- https://ubuntu.com/security/notices/USN-7445-1
- https://ubuntu.com/security/notices/USN-7448-1
- https://ubuntu.com/security/notices/USN-7455-1
- https://ubuntu.com/security/notices/USN-7455-2
- https://ubuntu.com/security/notices/USN-7455-3
- https://ubuntu.com/security/notices/USN-7455-4
- https://ubuntu.com/security/notices/USN-7455-5
- https://ubuntu.com/security/notices/USN-7459-1
- https://ubuntu.com/security/notices/USN-7459-2
- https://ubuntu.com/security/notices/USN-7460-1
- https://ubuntu.com/security/notices/USN-7461-1
- https://ubuntu.com/security/notices/USN-7461-2
- https://ubuntu.com/security/notices/USN-7461-3
- https://ubuntu.com/security/notices/USN-7462-1
- https://ubuntu.com/security/notices/USN-7462-2
- https://ubuntu.com/security/notices/USN-7475-1
- https://www.cve.org/CVERecord?id=CVE-2025-21703