CVE-2026-31421

Local kernel crash via cls_fw NULL dereference

Published Apr 13, 2026 · Updated Apr 13, 2026

NULL pointer dereference in the Linux Kernel allows local users to crash the kernel through cls_fw packet classification. The old fw_classify path obtains a NULL queue from tcf_block_q() for a shared block and dereferences q->handle instead of rejecting the old-method filter configuration. Exploitation requires an empty cls_fw filter on a shared block and a packet whose skb mark has a nonzero major value, causing kernel availability loss.

CVSS severity5.5
Medium
EPSS probability0.12%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

NULL pointer dereference in the Linux Kernel allows local users to crash the kernel through cls_fw packet classification. The old fw_classify path obtains a NULL queue from tcf_block_q() for a shared block and dereferences q->handle instead of rejecting the old-method filter configuration. Exploitation requires an empty cls_fw filter on a shared block and a packet whose skb mark has a nonzero major value, causing kernel availability loss.

The record

CVE
CVE-2026-31421
Published
Apr 13, 2026
Updated
Apr 13, 2026
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-476, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 13, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1abf272022cf1d18469405f47b4ec49c6a3125db <18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28
  2. Affected versionversion=1abf272022cf1d18469405f47b4ec49c6a3125db <3cb055df9e8625ce699a259d8178d67b37f2b160
  3. Affected versionversion=1abf272022cf1d18469405f47b4ec49c6a3125db <3d41f9a314afa94b1c7c7c75405920123220e8cd
  4. Affected versionversion=1abf272022cf1d18469405f47b4ec49c6a3125db <5cf41031922c154aa5ccda8bcdb0f5e6226582ec
  5. Affected versionversion=1abf272022cf1d18469405f47b4ec49c6a3125db <96426c348def662b06bfdc65be3002905604927a
  6. Affected versionversion=1abf272022cf1d18469405f47b4ec49c6a3125db <faeea8bbf6e958bf3c00cb08263109661975987c
  7. Affected versionversion=4.15

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linux Kernelversion=1abf272022cf1d18469405f47b4ec49c6a3125db <18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28; version=1abf272022cf1d18469405f47b4ec49c6a3125db <3cb055df9e8625ce699a259d8178d67b37f2b160; version=1abf272022cf1d18469405f47b4ec49c6a3125db <3d41f9a314afa94b1c7c7c75405920123220e8cd; version=1abf272022cf1d18469405f47b4ec49c6a3125db <5cf41031922c154aa5ccda8bcdb0f5e6226582ec; version=1abf272022cf1d18469405f47b4ec49c6a3125db <96426c348def662b06bfdc65be3002905604927a; version=1abf272022cf1d18469405f47b4ec49c6a3125db <faeea8bbf6e958bf3c00cb08263109661975987c; version=4.15

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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