CVE-2025-21971

Medium

In the Linux kernel, the following vulnerability has been resolved: net_sched: Prevent creation of classes with TC_H_ROOT The function qdisc_tree_reduce_backlog() uses TC_H_ROOT as a termination condition when traversing up the qdisc tree to update parent backlog counters. However, if a class is created with classid TC_H_ROOT, the traversal terminates prematurely at this class instead of reaching the actual root qdisc, causing parent statistics to be incorrectly maintained. In case of DRR, this could lead to a crash as reported by Mingi Cho. Prevent the creation of any Qdisc class with classid TC_H_ROOT (0xFFFFFFFF) across all qdisc types, as suggested by Jamal.

Package Linux Kernel
Published 2025-04-01
Last modified 2025-11-03
CVSS version 3.1
Patch available
Yes

CVSS 3.1 score

5.5

out of 10
Medium
Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
High
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness type

CWE-835

CVE-2025-21971 is a Infinite Loop vulnerability

What is Infinite Loop?

The product contains an iteration that does not exit even when it should. Learn more on MITRE CWE

Affected versions

Linux kernel versions 2.6.25 and later are affected. Fixed in 5.4.292, 5.10.236, 5.15.180, 6.1.132, 6.6.84, 6.12.20, 6.13.8, 6.14 and their respective stable series.

Affected from
≥ 2.6.25
Fixed in
✓ 5.4.292 5.4.x ✓ 5.10.236 5.10.x ✓ 5.15.180 5.15.x ✓ 6.1.132 6.1.x ✓ 6.6.84 6.6.x ✓ 6.12.20 6.12.x ✓ 6.13.8 6.13.x ✓ 6.14

References

The following references provide additional information about CVE-2025-21971 including vendor advisories, patch commits, exploit details, and third-party analysis. Links are sourced from the NIST NVD database.

8 patch commits total View all on NVD

Frequently asked questions

  • What is CVE-2025-21971?

    CVE-2025-21971 is a Medium severity Linux kernel vulnerability with a CVSS score of 5.5 out of 10 , classified as an Infinite Loop flaw (CWE-835) . It affects Linux kernel versions from 2.6.25 onward and has been patched in 5.4.292, 5.10.236, 5.15.180 and others. CVE-2025-21971 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

  • What is the CVSS score for CVE-2025-21971?

    CVE-2025-21971 has a CVSS score of 5.5 out of 10, rated Medium severity (CVSS 3.1). The vector string is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H .

  • Is there a patch available for CVE-2025-21971?

    Yes — CVE-2025-21971 has been patched. Fixed versions include 5.4.292, 5.10.236, 5.15.180 and others. If you are running Linux kernel 2.6.25 or later up to the fix versions, apply the relevant patch for your kernel branch.

  • Is CVE-2025-21971 actively exploited?

    No — CVE-2025-21971 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

  • What is Infinite Loop (CWE-835)?

    The product contains an iteration that does not exit even when it should. View CWE-835 on MITRE CWE →

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