---
id: "CVE-2021-22555"
kind: "vulnerability"
aliases: ["CVE-2021-22555"]
title: "A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in net/netfilter/x_tables.c"
severity: "high"
cvss: 8.3
epss: null
exploited: true
status: "open"
category: "infrastructure"
products: [{"name": "netapp c400 firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp c250 firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp h410c firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp h300s firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp h500s firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp h700s firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp h410s firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "linux kernel", "fixed": ["4.4.267"], "affected": ">= 2.6.19, < 4.4.267", "ecosystem": "vendor"}, {"name": "linux kernel", "fixed": ["4.9.267"], "affected": ">= 4.5, < 4.9.267", "ecosystem": "vendor"}, {"name": "linux kernel", "fixed": ["4.14.231"], "affected": ">= 4.10, < 4.14.231", "ecosystem": "vendor"}, {"name": "linux kernel", "fixed": ["4.19.188"], "affected": ">= 4.15, < 4.19.188", "ecosystem": "vendor"}, {"name": "linux kernel", "fixed": ["5.4.113"], "affected": ">= 4.20, < 5.4.113", "ecosystem": "vendor"}, {"name": "linux kernel", "fixed": ["5.10.31"], "affected": ">= 5.5, < 5.10.31", "ecosystem": "vendor"}, {"name": "linux kernel", "fixed": ["5.12"], "affected": ">= 5.11, < 5.12", "ecosystem": "vendor"}, {"name": "broadcom fabric operating system", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp fas 8300 firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp fas 8700 firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp aff a400 firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp aff a250 firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp aff 500f firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp h610c firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp h610s firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp h615c firmware", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp cloud backup", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp hci management node", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp solidfire", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "netapp solidfire baseboard management controller", "fixed": [], "affected": "", "ecosystem": "vendor"}, {"name": "Linux Kernel", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["exploited", "infrastructure", "kubernetes", "linux", "multi-user-hosts", "self-hosted"]
not_affected_if: ["managed-hosting", "user-namespaces-disabled"]
published_at: "2021-07-07T12:15:08+00:00"
first_seen_at: "2026-10-23T19:11:51+00:00"
updated_at: "2026-10-24T00:09:50+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-22555", "first_seen_at": "2026-10-23T19:11:51+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2021-22555", "first_seen_at": "2026-10-23T23:44:51+00:00"}]
---

# A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in net/netfilter/x_tables.c

A heap out-of-bounds write in the Linux kernel's netfilter code can corrupt kernel memory when a local user creates a user namespace. An attacker with a local account can gain root privileges or crash the machine, and CISA lists it as actively exploited.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:netapp c400 firmware affected ? fixed ?
- vendor:netapp c250 firmware affected ? fixed ?
- vendor:netapp h410c firmware affected ? fixed ?
- vendor:netapp h300s firmware affected ? fixed ?
- vendor:netapp h500s firmware affected ? fixed ?
- vendor:netapp h700s firmware affected ? fixed ?
- vendor:netapp h410s firmware affected ? fixed ?
- vendor:linux kernel affected >= 2.6.19, < 4.4.267 fixed 4.4.267
- vendor:linux kernel affected >= 4.5, < 4.9.267 fixed 4.9.267
- vendor:linux kernel affected >= 4.10, < 4.14.231 fixed 4.14.231
- vendor:linux kernel affected >= 4.15, < 4.19.188 fixed 4.19.188
- vendor:linux kernel affected >= 4.20, < 5.4.113 fixed 5.4.113
- vendor:linux kernel affected >= 5.5, < 5.10.31 fixed 5.10.31
- vendor:linux kernel affected >= 5.11, < 5.12 fixed 5.12
- vendor:broadcom fabric operating system affected ? fixed ?
- vendor:netapp fas 8300 firmware affected ? fixed ?
- vendor:netapp fas 8700 firmware affected ? fixed ?
- vendor:netapp aff a400 firmware affected ? fixed ?
- vendor:netapp aff a250 firmware affected ? fixed ?
- vendor:netapp aff 500f firmware affected ? fixed ?
- vendor:netapp h610c firmware affected ? fixed ?
- vendor:netapp h610s firmware affected ? fixed ?
- vendor:netapp h615c firmware affected ? fixed ?
- vendor:netapp cloud backup affected ? fixed ?
- vendor:netapp hci management node affected ? fixed ?
- vendor:netapp solidfire affected ? fixed ?
- vendor:netapp solidfire baseboard management controller affected ? fixed ?
- vendor:Linux Kernel affected ? fixed ?

## How to check

uname -r
Check your distro's kernel advisory for CVE-2021-22555 against your installed kernel build

## Fix

Upgrade to a patched kernel from your distribution (version unknown from the sources), then reboot.
If you cannot patch, follow CISA's BOD 22-01 guidance or the vendor's mitigation instructions.

## Timeline

- 2026-10-23T19:11:51+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2021-22555
- 2026-10-23T23:44:51+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2021-22555

## From the sources

Linux Kernel contains a heap out-of-bounds write vulnerability that could allow an attacker to gain privileges or cause a DoS (via heap memory corruption) through user name space.

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.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_