---
id: CVE-2021-34556
title: >-
  In the Linux kernel through 5.13.7, an unprivileged BPF program can obtain
  sensitive information from kernel memory via a Speculative Store Bypass
  side-channel attack because the protection mechanism neglects the possibility
  of uninitial…
summary: >-
  In the Linux kernel through 5.13.7, an unprivileged BPF program can obtain
  sensitive information from kernel memory via a Speculative Store Bypass
  side-channel attack because the protection mechanism neglects the possibility
  of uninitial…
severity: medium
cvss: 5.5
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N'
cwe:
  - CWE-203
vendor: linux
product: linux_kernel
affected:
  - linux_kernel <= 5.13.7
  - fedora = 33
  - fedora = 34
  - debian_linux = 9.0
published: '2021-08-02'
updated: '2026-10-08'
sourceUpdated: '2026-10-08T21:17:35.903'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2021-34556'
references:
  - url: 'http://www.openwall.com/lists/oss-security/2021/08/01/3'
    label: cve@mitre.org
  - url: >-
      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/?id=2039f26f3aca5b0e419b98f65dd36481337b86ee
    label: cve@mitre.org
  - url: >-
      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/?id=f5e81d1117501546b7be050c5fbafa6efd2c722c
    label: cve@mitre.org
  - url: 'https://lists.debian.org/debian-lts-announce/2021/10/msg00010.html'
    label: cve@mitre.org
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/565ZS55ZFEN62WVRRORT7R63RXW5F4T4/
    label: cve@mitre.org
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/6JKK6XNRZX5BT5QVYOKGVJ2BHFZAP5EX/
    label: cve@mitre.org
  - url: 'http://www.openwall.com/lists/oss-security/2021/08/01/3'
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/?id=2039f26f3aca5b0e419b98f65dd36481337b86ee
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/?id=f5e81d1117501546b7be050c5fbafa6efd2c722c
    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://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/565ZS55ZFEN62WVRRORT7R63RXW5F4T4/
    label: af854a3a-2127-422b-91ae-364da2661108
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/6JKK6XNRZX5BT5QVYOKGVJ2BHFZAP5EX/
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.00419
epssPercentile: 0.34239
ingestedAt: '2026-10-08T22:11:53.738Z'
---

## Overview

In the Linux kernel through 5.13.7, an unprivileged BPF program can obtain sensitive information from kernel memory via a Speculative Store Bypass side-channel attack because the protection mechanism neglects the possibility of uninitialized memory locations on the BPF stack.

## Affected

- `linux_kernel <= 5.13.7`
- `fedora = 33`
- `fedora = 34`
- `debian_linux = 9.0`

## Remediation

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