---
id: CVE-2021-33624
title: >-
  In kernel/bpf/verifier.c in the Linux kernel before 5.12.13, a branch can be
  mispredicted (e.g., because of type confusion) and consequently an
  unprivileged BPF program can read arbitrary memory locations via a
  side-channel attack, aka C…
summary: >-
  In kernel/bpf/verifier.c in the Linux kernel before 5.12.13, a branch can be
  mispredicted (e.g., because of type confusion) and consequently an
  unprivileged BPF program can read arbitrary memory locations via a
  side-channel attack, aka C…
severity: medium
cvss: 4.7
cvssVector: 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:N/A:N'
cwe:
  - CWE-843
vendor: linux
product: linux_kernel
affected:
  - linux_kernel < 5.12.13
  - debian_linux = 9.0
patched:
  - linux_kernel 5.12.13
published: '2021-06-23'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T21:17:35.550'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2021-33624'
references:
  - url: 'http://www.openwall.com/lists/oss-security/2021/06/21/1'
    label: cve@mitre.org
  - url: 'https://github.com/benschlueter/CVE-2021-33624'
    label: cve@mitre.org
  - url: >-
      https://github.com/torvalds/linux/commit/9183671af6dbf60a1219371d4ed73e23f43b49db
    label: cve@mitre.org
  - url: 'https://lists.debian.org/debian-lts-announce/2021/10/msg00010.html'
    label: cve@mitre.org
  - url: 'https://www.usenix.org/conference/usenixsecurity21/presentation/kirzner'
    label: cve@mitre.org
  - url: 'http://www.openwall.com/lists/oss-security/2021/06/21/1'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://github.com/torvalds/linux/commit/9183671af6dbf60a1219371d4ed73e23f43b49db
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://lists.debian.org/debian-lts-announce/2021/10/msg00010.html'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: 'https://www.usenix.org/conference/usenixsecurity21/presentation/kirzner'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
  - exploit-available
epss: 0.00922
epssPercentile: 0.59147
exploits:
  github: 1
  githubRepos:
    - 'https://github.com/benschlueter/CVE-2021-33624'
  checkedAt: '2026-10-09T10:30:31.214Z'
exploitAvailable: true
ingestedAt: '2026-10-08T22:11:53.737Z'
---

## Overview

In kernel/bpf/verifier.c in the Linux kernel before 5.12.13, a branch can be mispredicted (e.g., because of type confusion) and consequently an unprivileged BPF program can read arbitrary memory locations via a side-channel attack, aka CID-9183671af6db.

## Affected

- `linux_kernel < 5.12.13`
- `debian_linux = 9.0`

## Remediation

Upgrade past the affected range:

- `linux_kernel 5.12.13`