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Vulnerabilities

Vulnerability · 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 p…

Published Feb 18, 2025 · catalog updated Oct 15, 2026 · linux kernel

Check if you run it

No confirmed exploitation is on record for CVE-2025-21703. EPSS is 0.30%. Act only if a listed version of linux kernel is installed.

Gaps on this record

  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High7.8
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.30%
Remediation
Advisory link
Affected products
cpe linux/linux kernel

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe linux/linux kernel6.14

How to fix CVE-2025-21703

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2025-21703. EPSS is 0.30%. Act only if a listed version of linux kernel is installed.

Which versions are affected?

Compare what you have installed with linux/linux kernel 6.14. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-416: Use After Free. EPSS 0.30%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Feb 18, 2025 · NIST NVD

    Detected

    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

  2. Oct 15, 2026 · NIST NVD

    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

Sources

  • CVE.orgVulnerability recordCVE-2025-21703

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2025-21703

    30-day exploitation probability 0.3%

    first.org
  • NIST NVDVulnerability recordCVE-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 befor

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 16, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.