PT-2026-32347 · Linux · Linux Kernel

Published 2026-04-13 · Updated 2026-05-20 · CVE-2026-31421

Positive Technologies (AI Summary)

CVSS v3.1

5.5

Medium

Base vector

AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Name of the Vulnerable Software and Affected Versions Linux kernel (affected versions not specified)

Description A NULL pointer dereference occurs in the fw classify() function when an empty cls fw filter is attached to a shared block and a packet with a nonzero major skb mark is classified. This happens because the old-method path in fw classify() calls tcf block q() and attempts to dereference q->handle, but shared blocks leave block->q as NULL.

Recommendations At the moment, there is no information about a newer version that contains a fix for this vulnerability.

NULL Pointer Dereference

Weakness Enumeration

CWE-476

Related Identifiers

CVE-2026-31421

ECHO-1082-352E-3C42

Affected Products

Linux Kernel

References · 21

• https://git.kernel.org/stable/c/faeea8bbf6e958bf3c00cb08263109661975987c · Patch
• https://osv.dev/vulnerability/UBUNTU-CVE-2026-31421 · Vendor Advisory
• https://git.kernel.org/stable/c/febf64ca79a2d6540ab6e5e197fa0f4f7e84473e · Patch
• https://git.kernel.org/stable/c/3cb055df9e8625ce699a259d8178d67b37f2b160 · Patch
• https://osv.dev/vulnerability/ROOT-OS-UBUNTU-2404-CVE-2026-31421 · Vendor Advisory
• https://git.kernel.org/stable/c/d6d5bd62a09650856e1e2010eb09853eba0d64e1 · Patch
• https://git.kernel.org/stable/c/3d41f9a314afa94b1c7c7c75405920123220e8cd · Patch
• https://git.kernel.org/stable/c/18328eff2f97d1a6adcdb6d4a0f42f2f83a31e28 · Patch
• https://security-tracker.debian.org/tracker/CVE-2026-31421 · Vendor Advisory
• https://osv.dev/vulnerability/DEBIAN-CVE-2026-31421 · Vendor Advisory
• https://git.kernel.org/stable/c/96426c348def662b06bfdc65be3002905604927a · Patch
• https://git.kernel.org/stable/c/5cf41031922c154aa5ccda8bcdb0f5e6226582ec · Patch
• https://nvd.nist.gov/vuln/detail/CVE-2026-31421 · Security Note
• https://ubuntu.com/security/CVE-2026-31421 · Vendor Advisory
• https://osv.dev/vulnerability/ROOT-OS-UBUNTU-2204-CVE-2026-31421 · Vendor Advisory