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 a Infinite Loop flaw (CWE-835), affecting Linux kernel versions from 2.6.25 onward and 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. 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?

CVE-2025-21971 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

What is Infinite Loop (CWE-835)?

The product contains an iteration that does not exit even when it should. See MITRE CWE for full details: https://cwe.mitre.org/data/definitions/835.html

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

10 total

Kernel Git
https://git.kernel.org/stable/c/003d92c91cdb5a64b25a9a74cb8543aac9a8bb48

Patch
Kernel Git
https://git.kernel.org/stable/c/0c3057a5a04d07120b3d0ec9c79568fceb9c921e

Patch
Kernel Git
https://git.kernel.org/stable/c/5c3ca9cb48b51bd72bf76b8b05e24f3cd53db5e7

Patch
Kernel Git
https://git.kernel.org/stable/c/78533c4a29ac3aeddce4b481770beaaa4f3bfb67

Patch
Kernel Git
https://git.kernel.org/stable/c/7a82fe67a9f4d7123d8e5ba8f0f0806c28695006

Patch

Showing 5 of 10 references View all on NVD

Details

CVE ID CVE-2025-21971

Severity Medium

CVSS score 5.5 / 10

CVSS version 3.1

Published 2025-04-01

Modified 2025-11-03

KEV No

Patch

Yes

Package linux

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.