---
title: "CVE-2021-22555: Linux Kernel Heap Out-of-Bounds Write Vulnerability"
url: https://erroneo.us/security/cve/CVE-2021-22555/
description: "CVE-2021-22555 (Linux Kernel): Exploited in the wild (CISA KEV). A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in…"
type: vulnerability-record
section: "Security Digest"
date_published: 2021-07-07
date_modified: 2025-12-30
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2021-22555"
kev: true
cvss: 8.3
epss: 0.78684
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2021-22555: Linux Kernel Heap Out-of-Bounds Write Vulnerability

**Signal:** Exploited: patch now if you run it. CISA has confirmed exploitation in the wild. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Yes, if you run Linux Kernel. CISA added this CVE to its Known Exploited Vulnerabilities catalog on 2025-10-06, which means there is reliable evidence of exploitation in the wild. US federal agencies must remediate by 2025-10-27 ; treat that as the outer limit, not the target.
- EPSS 78.7% , percentile 99.6: FIRST’s model estimates a 78.7% chance of exploitation activity in the next 30 days, higher than 99.6% of all scored CVEs (very high). EPSS is a probability, not a verdict.

## What it is

A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in net/netfilter/xtables.c. This allows an attacker to gain privileges or cause a DoS (via heap memory corruption) through user name space

## Affected products (CVE record)

- n/a Linux Kernel: 2.6.19-rc1 < unspecified

## Severity

- Google CVSS 3.1: 8.3 `CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H`

## Exploitation

- CISA KEV: added 2025-10-06; federal due date 2025-10-27. Known ransomware use: Unknown.
- CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
- CISA SSVC assessment: exploitation active , automatable no , technical impact total .
- FIRST EPSS (model of 2026-10-21): 78.68% probability of exploitation activity in the next 30 days; percentile 99.6.

## Sources

- [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=9fa492cdc160cd27ce1046cb36f47d3b2b1efa21)
- [Listed in CISA KEV notes (git.kernel.org)](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=b29c457a6511435960115c0f548c4360d5f4801d)
- [Listed in CISA KEV notes (security.netapp.com)](https://security.netapp.com/advisory/ntap-20210805-0010/)
- [Listed in CISA KEV notes (github.com)](https://github.com/google/security-research/security/advisories/GHSA-xxx5-8mvq-3528)
- [CVE.org record CVE-2021-22555](https://www.cve.org/CVERecord?id=CVE-2021-22555)
- [NVD entry CVE-2021-22555](https://nvd.nist.gov/vuln/detail/CVE-2021-22555)
- [CISA Known Exploited Vulnerabilities catalog entry](https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-22555)
- [packetstormsecurity.com](http://packetstormsecurity.com/files/163528/Linux-Kernel-Netfilter-Heap-Out-Of-Bounds-Write.html)
- [packetstormsecurity.com](http://packetstormsecurity.com/files/163878/Kernel-Live-Patch-Security-Notice-LSN-0080-1.html)
- [packetstormsecurity.com](http://packetstormsecurity.com/files/164155/Kernel-Live-Patch-Security-Notice-LSN-0081-1.html)
- [packetstormsecurity.com](http://packetstormsecurity.com/files/164437/Netfilter-x_tables-Heap-Out-Of-Bounds-Write-Privilege-Escalation.html)
- [packetstormsecurity.com](http://packetstormsecurity.com/files/165477/Kernel-Live-Patch-Security-Notice-LSN-0083-1.html)

---
Source page: https://erroneo.us/security/cve/CVE-2021-22555/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt