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

Q: How do I fix CVE-2021-22555?

c400 firmware: mitigate or apply the listed mitigation; c250 firmware: mitigate or apply the listed mitigation; h410c firmware: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2021-22555 being exploited?

Yes. CVE-2021-22555 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

Q: What does CVE-2021-22555 affect?

CVE-2021-22555 affects c400 firmware, c250 firmware, h410c firmware. Severity is high (CVSS 8.3). A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in net/netfilter/x_tables.c. This allows an attacker to gain privileges or cause a DoS (via heap memory corruption) through user name space

Q: How urgent is CVE-2021-22555?

Priority 89/100. High severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Public exploit reference; On your watchlist

Patch now

HIGH 8.3EXPLOITEDWATCHLISTMITIGATEMITIGATEMITIGATE

CVE-2021-22555 is a high-severity flaw (CVSS 8.3) affecting c400 firmware, c250 firmware, h410c firmware, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

High severity
EPSS top 1%: very likely to be exploited
Exploited in the wild (CISA KEV)
Public exploit reference
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	8.3 (High)
Attack vector	Adjacent network
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	78.7% (top 1%)
CISA exploited list	Yes, fix due 2025-10-27
Weakness	CWE-787
Published	2021-07-07
Last modified	2026-10-13

Publisher (CNA): Google Inc. · Vendor: netapp

Last updated 2026-10-13 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-07-07 12:15 UTCPublished CVE record published
2025-10-06Exploited Added to the CISA Known Exploited Vulnerabilities list
2025-10-27Deadline CISA due date for US federal agencies to patch
2026-10-13 18:25 UTCUpdated Record last modified

netapp c400 firmware MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

netapp c250 firmware MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

netapp h410c firmware MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

netapp h300s firmware MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

netapp h500s firmware MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

netapp h700s firmware MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · bitcoin-core-selinux · FIXED · 0.3-2.fc46 · FEDORA-2026-51fc806272 · source

sudo dnf upgrade --advisory=FEDORA-2026-51fc806272

Fedora ELN · guestfs-tools · FIXED · 1.57.5-1.eln159 · FEDORA-2026-9577c5ec16 · source

sudo dnf upgrade --advisory=FEDORA-2026-9577c5ec16

Ubuntu 22.04 · linux · NOT AFFECTED

Ubuntu 20.04 · linux · FIXED · 5.4.0-74.83

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "5.4.0-74.83" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 24.04 · linux · NOT AFFECTED

Ubuntu 24.10 · linux · NOT AFFECTED

Ubuntu 25.04 · linux · NOT AFFECTED

Debian 12 · linux · FIXED · 5.10.38-1

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "5.10.38-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · linux · FIXED · 5.10.38-1

sudo apt update && sudo apt install --only-upgrade linux dpkg --compare-versions "$(dpkg-query -W -f='${Version}' linux)" ge "5.10.38-1" && echo PATCHED || echo STILL-VULNERABLE

RHEL 6 Extended Lifecycle Support - EXTENSION · kernel · FIXED · kernel-2.6.32-754.58.1.el6

sudo dnf upgrade --advisory=RHSA-2025:17733 rpm -q kernel

RHEL 7 · kernel-rt · FIXED · kernel-rt-3.10.0-1160.41.1.rt56.1181.el7

sudo dnf upgrade --advisory=RHSA-2021:3328 rpm -q kernel-rt

RHEL 7 · kernel · FIXED · kernel-3.10.0-1160.41.1.el7

sudo dnf upgrade --advisory=RHSA-2021:3327 rpm -q kernel

RHEL 7.2 Advanced Update Support · kernel · FIXED · kernel-3.10.0-327.100.1.el7

sudo dnf upgrade --advisory=RHSA-2021:3399 rpm -q kernel

RHEL 7.3 Advanced Update Support · kernel · FIXED · kernel-3.10.0-514.92.1.el7

sudo dnf upgrade --advisory=RHSA-2021:3321 rpm -q kernel

Amazon Linux 2 · see advisory · FIXED · ALAS2-2021-1627 · source

sudo yum update --advisory=ALAS2-2021-1627

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

GitHub PoC: veritas501/CVE-2021-22555-PipeVersion (40 stars)
GitHub PoC: xyjl-ly/CVE-2021-22555-Exploit (14 stars)
GitHub PoC: cgwalters/container-cve-2021-22555 (4 stars)
Write-up: git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c
Write-up: git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c
Write-up: github.com/google/security-research/security/advisories/GHSA-xxx5-8mvq-3528
Exploit-DB: Linux Kernel 2.6.19 < 5.9 - 'Netfilter Local Privilege Escalation
Metasploit: Netfilter x_tables Heap OOB Write Privilege Escalation

Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-22555?

c400 firmware: mitigate or apply the listed mitigation; c250 firmware: mitigate or apply the listed mitigation; h410c firmware: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-22555 being exploited?

Yes. CVE-2021-22555 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2021-22555 affect?

CVE-2021-22555 affects c400 firmware, c250 firmware, h410c firmware. Severity is high (CVSS 8.3). A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in net/netfilter/x_tables.c. This allows an attacker to gain privileges or cause a DoS (via heap memory corruption) through user name space

How urgent is CVE-2021-22555?

Priority 89/100. High severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Public exploit reference; On your watchlist

Software pages

Linux kernel vulnerabilities

Related CVEs

CVE-2024-26735 MEDIUM 5.5 UPGRADE MITIGATE In the Linux kernel, the following vulnerability has been resolved: ipv6: sr: fix possible use-after-free and
CVE-2021-22600 MEDIUM 6.6 EXPLOITED MITIGATE MITIGATE Linux Kernel Privilege Escalation Vulnerability

References

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