---
id: CVE-2026-74544
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds

  u32_change() copies the user-provided tc_u32_sel.offshift (unsigned char,
  0-255) into the kernel k…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds

  u32_change() copies the user-provided tc_u32_sel.offshift (unsigned char,
  0-255) into the kernel k…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    9990cac513e8b191de2ee589051ea7ebf3cee940
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    313cb9ffc4101a885d791facf4b5ea3d5e06144d
  - >-
    Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <
    aef96eead2860cbfa371e4471d4f04412213b958
  - Linux 2.6.12
published: '2026-08-15'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T11:17:47.287'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-74544'
references:
  - url: 'https://git.kernel.org/stable/c/313cb9ffc4101a885d791facf4b5ea3d5e06144d'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9990cac513e8b191de2ee589051ea7ebf3cee940'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/aef96eead2860cbfa371e4471d4f04412213b958'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
epss: 0.00165
epssPercentile: 0.05338
ingestedAt: '2026-10-15T11:00:41.671Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

net/sched: cls_u32: validate offshift to prevent shift-out-of-bounds

u32_change() copies the user-provided tc_u32_sel.offshift (unsigned char,
0-255) into the kernel knode object without bounds validation. When a
packet later hits u32_classify() with TC_U32_VAROFFSET set, it evaluates
`ntohs(offmask & *data) >> offshift` where the left operand is a 16-bit
value promoted to a 32-bit int. Any offshift >= 32 is undefined behavior
per C11 6.5.7p3, triggerable by an unprivileged user via user/network
namespaces.

UBSAN: shift-out-of-bounds in net/sched/cls_u32.c:236:43
shift exponent 32 is too large for 32-bit type int

Fix this by rejecting offshift >= 16 during filter creation in
u32_change().

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.