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Fencer Vulns
medium 5.5

CVE-2025-37953 json

sch_htb: make htb_deactivate() idempotent

published 2025-05-20 17 mo ago modified 2026-06-17 4 mo ago also EUVD-2025-15902

cvss
5.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 9%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

sch_htb: make htb_deactivate() idempotent

Alan reported a NULL pointer dereference in htb_next_rb_node() after we made htb_qlen_notify() idempotent.

It turns out in the following case it introduced some regression:

htb_dequeue_tree(): |-> fq_codel_dequeue() |-> qdisc_tree_reduce_backlog() |-> htb_qlen_notify() |-> htb_deactivate() |-> htb_next_rb_node() |-> htb_deactivate()

For htb_next_rb_node(), after calling the 1st htb_deactivate(), the clprio[prio]->ptr could be already set to NULL, which means htb_next_rb_node() is vulnerable here.

For htb_deactivate(), although we checked qlen before calling it, in case of qlen==0 after qdisc_tree_reduce_backlog(), we may call it again which triggers the warning inside.

To fix the issues here, we need to:

1) Make htb_deactivate() idempotent, that is, simply return if we already call it before. 2) Make htb_next_rb_node() safe against ptr==NULL.

Many thanks to Alan for testing and for the reproducer.

Patch / fix

  • Linux Linux 6.1.139, 6.6.91, 6.12.29, 6.14.7
  • linux Debian 12 6.1.140-1
  • linux Debian 14, Debian 13 6.12.29-1

debian advisories DEBIAN-CVE-2025-37953

  • kernel-coco SLE Module for Confidential Computing Technical Preview 15 SP6 6.4.0-15061.28.coco15sp6.1
  • kernel-syms-coco SLE Module for Confidential Computing Technical Preview 15 SP6 6.4.0-15061.28.coco15sp6.1
  • kernel-coco_debug SLE Module for Confidential Computing Technical Preview 15 SP6 6.4.0-15061.28.coco15sp6.1
  • kernel-source-coco SLE Module for Confidential Computing Technical Preview 15 SP6 6.4.0-15061.28.coco15sp6.1
  • kernel-64kb SLES 15 SP4-LTSS, SLE High Performance Computing 15 SP4-LTSS, SLE High Performance Computing 15 SP4-ESPOS 5.14.21-150400.24.170.2
  • kernel-syms SLES for SAP 15 SP4, SLES 15 SP4-LTSS, SLE High Performance Computing 15 SP4-LTSS +3 more 5.14.21-150400.24.170.1
  • kernel-source SLES for SAP 15 SP4, SLES 15 SP4-LTSS, SLE High Performance Computing 15 SP4-LTSS +3 more 5.14.21-150400.24.170.1
  • kernel-default SLES for SAP 15 SP4, SLES 15 SP4-LTSS, SLE Micro 5.4 +6 more 5.14.21-150400.24.170.2

suse advisories SUSE-SU-2025:02923-1SUSE-SU-2025:02537-1SUSE-SU-2025:02333-1SUSE-SU-2025:02322-1SUSE-SU-2025:02321-1SUSE-SU-2025:02320-1

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-2025-37953 updated cvss 5.5

kernel: Linux kernel: sch_htb NULL pointer dereference

  • 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 Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux 10 kernel
    not affected: vulnerable code not present

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

Exploit prediction

0.19% chance of exploitation in the next 30 days, higher than 9% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
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
Technology feeds

References

Sources

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