---
id: CVE-2021-33033
title: >-
  The Linux kernel before 5.11.14 has a use-after-free in cipso_v4_genopt in
  net/ipv4/cipso_ipv4.c because the CIPSO and CALIPSO refcounting for the DOI
  definitions is mishandled, aka CID-ad5d07f4a9cd
summary: >-
  The Linux kernel before 5.11.14 has a use-after-free in cipso_v4_genopt in
  net/ipv4/cipso_ipv4.c because the CIPSO and CALIPSO refcounting for the DOI
  definitions is mishandled, aka CID-ad5d07f4a9cd. This leads to writing an
  arbitrary va…
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 >= 2.6.28, < 4.9.298'
  - 'linux_kernel >= 4.10, < 4.14.226'
  - 'linux_kernel >= 4.15, < 4.19.181'
  - 'linux_kernel >= 4.20, < 5.4.106'
  - 'linux_kernel >= 5.5, < 5.10.24'
  - 'linux_kernel >= 5.11, < 5.11.7'
patched:
  - linux_kernel 5.11.7
published: '2021-05-14'
updated: '2026-08-05'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2021-33033'
references:
  - url: 'https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.11.14'
    label: cve@mitre.org
  - url: 'https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.11.7'
    label: cve@mitre.org
  - url: >-
      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1165affd484889d4986cf3b724318935a0b120d8
    label: cve@mitre.org
  - url: >-
      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ad5d07f4a9cd671233ae20983848874731102c08
    label: cve@mitre.org
  - url: >-
      https://sites.google.com/view/syzscope/kasan-use-after-free-read-in-cipso_v4_genopt
    label: cve@mitre.org
  - url: >-
      https://syzkaller.appspot.com/bug?id=96e7d345748d8814901c91cd92084ed04b46701e
    label: cve@mitre.org
  - url: 'https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.11.14'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.11.7'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1165affd484889d4986cf3b724318935a0b120d8
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ad5d07f4a9cd671233ae20983848874731102c08
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://sites.google.com/view/syzscope/kasan-use-after-free-read-in-cipso_v4_genopt
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://syzkaller.appspot.com/bug?id=96e7d345748d8814901c91cd92084ed04b46701e
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.00566
epssPercentile: 0.44571
ingestedAt: '2026-08-05T18:50:24.770Z'
---

## Overview

The Linux kernel before 5.11.14 has a use-after-free in cipso_v4_genopt in net/ipv4/cipso_ipv4.c because the CIPSO and CALIPSO refcounting for the DOI definitions is mishandled, aka CID-ad5d07f4a9cd. This leads to writing an arbitrary value.

## Affected

- `linux_kernel >= 2.6.28, < 4.9.298`
- `linux_kernel >= 4.10, < 4.14.226`
- `linux_kernel >= 4.15, < 4.19.181`
- `linux_kernel >= 4.20, < 5.4.106`
- `linux_kernel >= 5.5, < 5.10.24`
- `linux_kernel >= 5.11, < 5.11.7`

## Remediation

Upgrade past the affected range:

- `linux_kernel 5.11.7`