---
id: CVE-2023-4921
title: >-
  A use-after-free vulnerability in the Linux kernel's net/sched: sch_qfq
  component can be exploited to achieve local privilege escalation.


  When the plug qdisc is used as a class of the qfq qdisc, sending network
  packets triggers use-afte…
summary: >-
  A use-after-free vulnerability in the Linux kernel's net/sched: sch_qfq
  component can be exploited to achieve local privilege escalation.


  When the plug qdisc is used as a class of the qfq qdisc, sending network
  packets triggers use-afte…
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'
cwe:
  - CWE-416
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 3.8, < 4.14.326'
  - 'linux_kernel >= 4.15, < 4.19.295'
  - 'linux_kernel >= 4.20, < 5.4.257'
  - 'linux_kernel >= 5.5, < 5.10.195'
  - 'linux_kernel >= 5.11, < 5.15.132'
  - 'linux_kernel >= 5.16, < 6.1.54'
  - 'linux_kernel >= 6.2, < 6.5.4'
  - debian_linux = 10.0
patched:
  - linux_kernel 6.5.4
published: '2023-09-12'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T22:17:18.763'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2023-4921'
references:
  - url: >-
      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8fc134fee27f2263988ae38920bc03da416b03d8
    label: cve-coordination@google.com
  - url: 'https://kernel.dance/8fc134fee27f2263988ae38920bc03da416b03d8'
    label: cve-coordination@google.com
  - url: 'https://lists.debian.org/debian-lts-announce/2023/10/msg00027.html'
    label: cve-coordination@google.com
  - url: 'https://lists.debian.org/debian-lts-announce/2024/01/msg00004.html'
    label: cve-coordination@google.com
  - url: >-
      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=8fc134fee27f2263988ae38920bc03da416b03d8
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://kernel.dance/8fc134fee27f2263988ae38920bc03da416b03d8'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2023/10/msg00027.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2024/01/msg00004.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-398330.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-769027.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-794697.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00418
epssPercentile: 0.34476
ingestedAt: '2026-10-14T23:00:02.003Z'
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2024-05-10T04:00:09.695048Z'
---

## Overview

A use-after-free vulnerability in the Linux kernel's net/sched: sch_qfq component can be exploited to achieve local privilege escalation.

When the plug qdisc is used as a class of the qfq qdisc, sending network packets triggers use-after-free in qfq_dequeue() due to the incorrect .peek handler of sch_plug and lack of error checking in agg_dequeue().

We recommend upgrading past commit 8fc134fee27f2263988ae38920bc03da416b03d8.

## Affected

- `linux_kernel >= 3.8, < 4.14.326`
- `linux_kernel >= 4.15, < 4.19.295`
- `linux_kernel >= 4.20, < 5.4.257`
- `linux_kernel >= 5.5, < 5.10.195`
- `linux_kernel >= 5.11, < 5.15.132`
- `linux_kernel >= 5.16, < 6.1.54`
- `linux_kernel >= 6.2, < 6.5.4`
- `debian_linux = 10.0`

## Remediation

Upgrade past the affected range:

- `linux_kernel 6.5.4`