CVE-2025-21971

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.

CVSS 3.1

5.5CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS

0.2% chance of exploitation in the next 30 days; higher than 13% of CVEs (scores of 2026-10-25)

CWE

CWE-835

Published

2025-04-01

Modified

2026-10-15

Record from

the NVD, synced 2026-10-19

Affected

• linux:linux_kernel

References

• https://git.kernel.org/stable/c/003d92c91cdb5a64b25a9a74cb8543aac9a8bb48
• https://git.kernel.org/stable/c/0c3057a5a04d07120b3d0ec9c79568fceb9c921e
• https://git.kernel.org/stable/c/5c3ca9cb48b51bd72bf76b8b05e24f3cd53db5e7
• https://git.kernel.org/stable/c/78533c4a29ac3aeddce4b481770beaaa4f3bfb67
• https://git.kernel.org/stable/c/7a82fe67a9f4d7123d8e5ba8f0f0806c28695006

Check your stackJSON