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Fencer Vulns
high 7.8

CVE-2025-21971 json

net_sched: Prevent creation of classes with TC_H_ROOT

published 2025-04-01 19 mo ago modified 2026-10-15 24 d ago also EUVD-2025-9349

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 13%
public exploits
0
none known

Summary

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.

Patch / fix

  • Linux Linux 5.4.292, 5.10.236, 5.15.180, 6.1.132, 6.6.84, 6.12.20, 6.13.8, 6.14
  • linux Debian 12 6.1.133-1
  • linux Debian 14, Debian 13 6.12.20-1

debian advisories DEBIAN-CVE-2025-21971

  • linux Ubuntu 20.04 LTS 5.4.0-216.236
  • linux Ubuntu 22.04 LTS 5.15.0-140.150
  • linux Ubuntu 24.04 LTS 6.8.0-60.63
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1146.156
  • linux-aws Ubuntu 22.04 LTS 5.15.0-1084.91
  • linux-aws Ubuntu 24.04 LTS 6.8.0-1029.31
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1149.158
  • linux-gcp Ubuntu 22.04 LTS 5.15.0-1083.92

ubuntu advisories UBUNTU-CVE-2025-21971

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-livepatch-MICRO-6-0-RT_Update_3 Linux Micro 6.0 14-1.2
  • kernel-livepatch-MICRO-6-0-RT_Update_2 Linux Micro 6.1, Linux Micro 6.0 14-1.1
  • kernel-livepatch-MICRO-6-0_Update_2 Linux Micro 6.1, Linux Micro 6.0 14-1.1
  • kernel-livepatch-MICRO-6-0_Update_4 Linux Micro 6.1, Linux Micro 6.0 12-1.2
  • kernel-livepatch-MICRO-6-0_Update_5 Linux Micro 6.1, Linux Micro 6.0 10-1.2
  • kernel-livepatch-MICRO-6-0_Update_3 Linux Micro 6.0 14-1.2
  • kernel-livepatch-MICRO-6-0-RT_Update_5 Linux Micro 6.1, Linux Micro 6.0 10-1.1
  • kernel-livepatch-MICRO-6-0-RT_Update_4 Linux Micro 6.1, Linux Micro 6.0 11-1.1

suse advisories SUSE-SU-2025:4123-1SUSE-SU-2025:20891-1SUSE-SU-2025:20890-1SUSE-SU-2025:20920-1SUSE-SU-2025:20886-1SUSE-SU-2025:20909-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-21971 updated cvss 5.5

kernel: net_sched: Prevent creation of classes with TC_H_ROOT

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel
    affected: no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
24 d ago

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 5.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
  • CWE-835 Loop with Unreachable Exit Condition
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.