---
id: CVE-2021-33034
title: >-
  In the Linux kernel before 5.12.4, net/bluetooth/hci_event.c has a
  use-after-free when destroying an hci_chan, aka CID-5c4c8c954409
summary: >-
  In the Linux kernel before 5.12.4, net/bluetooth/hci_event.c has a
  use-after-free when destroying an hci_chan, aka CID-5c4c8c954409. This leads
  to writing an arbitrary value.
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 < 4.4.269
  - 'linux_kernel >= 4.5, < 4.9.269'
  - 'linux_kernel >= 4.10, < 4.14.233'
  - 'linux_kernel >= 4.15, < 4.19.191'
  - 'linux_kernel >= 4.20, < 5.4.119'
  - 'linux_kernel >= 5.5, < 5.10.37'
  - 'linux_kernel >= 5.11, < 5.11.21'
  - 'linux_kernel >= 5.12, < 5.12.4'
  - fedora = 34
  - debian_linux = 9.0
patched:
  - linux_kernel 5.12.4
published: '2021-05-14'
updated: '2026-08-13'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2021-33034'
references:
  - url: 'https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.12.4'
    label: cve@mitre.org
  - url: >-
      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5c4c8c9544099bb9043a10a5318130a943e32fc3
    label: cve@mitre.org
  - url: 'https://lists.debian.org/debian-lts-announce/2021/06/msg00019.html'
    label: cve@mitre.org
  - url: 'https://lists.debian.org/debian-lts-announce/2021/06/msg00020.html'
    label: cve@mitre.org
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GI7Z7UBWBGD3ABNIL2DC7RQDCGA4UVQW/
    label: cve@mitre.org
  - url: >-
      https://sites.google.com/view/syzscope/kasan-use-after-free-read-in-hci_send_acl
    label: cve@mitre.org
  - url: >-
      https://syzkaller.appspot.com/bug?id=2e1943a94647f7732dd6fc60368642d6e8dc91b1
    label: cve@mitre.org
  - url: 'https://cdn.kernel.org/pub/linux/kernel/v5.x/ChangeLog-5.12.4'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5c4c8c9544099bb9043a10a5318130a943e32fc3
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2021/06/msg00019.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2021/06/msg00020.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GI7Z7UBWBGD3ABNIL2DC7RQDCGA4UVQW/
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://sites.google.com/view/syzscope/kasan-use-after-free-read-in-hci_send_acl
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://syzkaller.appspot.com/bug?id=2e1943a94647f7732dd6fc60368642d6e8dc91b1
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
  - exploit-available
epss: 0.00819
epssPercentile: 0.55311
ingestedAt: '2026-08-13T20:06:14.938Z'
exploits:
  github: 1
  githubRepos:
    - >-
      https://github.com/Trinadh465/device_renesas_kernel_AOSP10_r33_CVE-2021-33034
  checkedAt: '2026-09-25T08:20:38.546Z'
exploitAvailable: true
---

## Overview

In the Linux kernel before 5.12.4, net/bluetooth/hci_event.c has a use-after-free when destroying an hci_chan, aka CID-5c4c8c954409. This leads to writing an arbitrary value.

## Affected

- `linux_kernel < 4.4.269`
- `linux_kernel >= 4.5, < 4.9.269`
- `linux_kernel >= 4.10, < 4.14.233`
- `linux_kernel >= 4.15, < 4.19.191`
- `linux_kernel >= 4.20, < 5.4.119`
- `linux_kernel >= 5.5, < 5.10.37`
- `linux_kernel >= 5.11, < 5.11.21`
- `linux_kernel >= 5.12, < 5.12.4`
- `fedora = 34`
- `debian_linux = 9.0`

## Remediation

Upgrade past the affected range:

- `linux_kernel 5.12.4`