VulnerabilityPublished 20 May 2025Updated 5 Nov 2026

CVE-2025-37932: Linux kernel · sch_htb: make htb_qlen_notify() idempotent

Affects Linux kernelSource GCVE Database

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Not known to be exploited.

Data as of 5 Nov 2026, 22:03 UTC

Severity

Unrated

Rated by Threat Radar · No CVSS score from NVD or the CNA

Thin evidence

One scorer or none

Exploitation evidence

Disclosed: evidence found.
CVE published 20 May 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

AI-suggested

A fix has been implemented in the Linux kernel to make htb_qlen_notify() idempotent. Users should update to the fixed kernel version once available. Since no exploit is known and this is an internal kernel function improvement, no additional mitigation steps are required.

Description

A vulnerability in the Linux kernel's sch_htb component was addressed by making the htb_qlen_notify() function idempotent. Previously, this function always deactivated the HTB class and could trigger warnings if called multiple times when already deactivated, causing issues for callers like fq_codel_dequeue(). The fix improves stability and reliability of the queueing discipline operations.

Impact

The issue could cause warnings or instability in the Linux kernel's traffic control subsystem when htb_qlen_notify() is called multiple times unnecessarily. This may affect network traffic scheduling reliability and performance. However, no exploitation in the wild is known, and the impact is limited to internal kernel queue management behavior.

Summary

The Linux kernel's sch_htb module contained a flaw where the htb_qlen_notify() function was not idempotent. It always deactivated the HTB class regardless of its current state, potentially triggering warnings if the class was already deactivated. This behavior could negatively affect callers such as fq_codel_dequeue() that rely on htb_qlen_notify(). The vulnerability was resolved by modifying htb_qlen_notify() to be idempotent, preventing unnecessary deactivation and warnings, thereby easing the operation of qdisc_tree_reduce_backlog() and related functions.

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 5 Nov 2026, 22:03 UTC

Technical details

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