CVE-2025-37953

Medium

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.

Package Linux Kernel
Published 2025-05-20
Last modified 2025-12-17
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-476

CVE-2025-37953 is a NULL Pointer Dereference vulnerability

What is NULL Pointer Dereference?

The product dereferences a pointer that it expects to be valid but is NULL, typically causing a crash. Learn more on MITRE CWE

Affected versions

Linux kernel versions 6.1.138, 6.6.90, 6.12.28, 6.14.6 and later are affected. Fixed in 6.1.139, 6.6.91, 6.12.29, 6.14.7 and their respective stable series.

Affected from
≥ 6.1.138 ≥ 6.6.90 ≥ 6.12.28 ≥ 6.14.6
Fixed in
✓ 6.1.139 6.1.x ✓ 6.6.91 6.6.x ✓ 6.12.29 6.12.x ✓ 6.14.7 6.14.x

References

9 total
Showing 5 of 9 references View all on NVD

Frequently asked questions

  • What is CVE-2025-37953?

    CVE-2025-37953 is a Medium severity Linux kernel vulnerability with a CVSS score of 5.5 out of 10 , classified as a NULL Pointer Dereference flaw (CWE-476) . It affects Linux kernel versions from 6.1.138 onward and has been patched in 6.1.139, 6.6.91, 6.12.29 and others. CVE-2025-37953 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

  • What is the CVSS score for CVE-2025-37953?

    CVE-2025-37953 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-2025-37953?

    Yes. CVE-2025-37953 has been patched. Fixed versions include 6.1.139, 6.6.91, 6.12.29 and others. If you are running Linux kernel 6.1.138 or later up to the fix versions, apply the relevant patch for your kernel branch.

  • Is CVE-2025-37953 actively exploited?

    No. CVE-2025-37953 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

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