CVE-2025-37953 Affecting kernel package, versions *


Severity

Recommended
medium

Based on CentOS security rating.

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  • Snyk IDSNYK-CENTOS6-KERNEL-10190312
  • published21 May 2025
  • disclosed20 May 2025

Introduced: 20 May 2025

NewCVE-2025-37953  (opens in a new tab)

How to fix?

There is no fixed version for Centos:6 kernel.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel package and not the kernel package as distributed by Centos. See How to fix? for Centos:6 relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1