CVE-2021-22555

Confirmed PUBLISHED

Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACE

Linux · Linux Kernel

1 day faster than CISA KEV

Exploited in the wild PoC available

Recommended Action

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

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Confidence

Confirmed

Exploitation Status

Exploited in the wild

Observed in Sensors

Attempts (30d)

—

Unique Attacker IPs

—

CISA KEV

In CISA KEV

CVSS / EPSS

8.3 High EPSS 78.7%

At a Glance

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

cisa linux

CVE Published: Jul 07, 2021
Exploitation Reported: Jun 01, 2026
CVSS: 8.3 High
EPSS: 78.7%

No user interaction Unauthenticated

Affected Versions

Vendor	Product	Version	Status
n/a	Linux Kernel	2.6.19-rc1 to < unspecified	Affected

CVE References

GitHub — google/security-research github.com · CVE Record https://github.com/google/security-research/security/advisories/GHSA-...
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/... git.kernel.org · CVE Record https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co...
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/... git.kernel.org · CVE Record https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/co...
packetstormsecurity.com/files/163528/Linux-Kernel-Netfilter-Heap-Out... packetstormsecurity.com · CVE Record http://packetstormsecurity.com/files/163528/Linux-Kernel-Netfilter-He...
security.netapp.com/advisory/ntap-20210805-0010 security.netapp.com · CVE Record https://security.netapp.com/advisory/ntap-20210805-0010/

Show 4 more references

packetstormsecurity.com/files/163878/Kernel-Live-Patch-Security-Noti... packetstormsecurity.com · CVE Record http://packetstormsecurity.com/files/163878/Kernel-Live-Patch-Securit...
packetstormsecurity.com/files/164155/Kernel-Live-Patch-Security-Noti... packetstormsecurity.com · CVE Record http://packetstormsecurity.com/files/164155/Kernel-Live-Patch-Securit...
packetstormsecurity.com/files/164437/Netfilter-x_tables-Heap-Out-Of-... packetstormsecurity.com · CVE Record http://packetstormsecurity.com/files/164437/Netfilter-x_tables-Heap-O...
packetstormsecurity.com/files/165477/Kernel-Live-Patch-Security-Noti... packetstormsecurity.com · CVE Record http://packetstormsecurity.com/files/165477/Kernel-Live-Patch-Securit...

Recommended Actions

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.
Check enrichment artifacts for scanner coverage and available PoCs before rolling remediation validation.
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Known Exploited Vulnerability Sources

Catalogues that list this CVE as a known exploited vulnerability.

Per-source evidence links for KEV attestations are available through the KEVIntel Pro API.

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Source	Added
CVE First	2026-06-01 10:41 UTC
CISA	2026-06-02 14:05 UTC

Scanner Artifacts

Nuclei and Metasploit references linked to this CVE.

Scanner	Reference	Detected
Metasploit	https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/linux/local/netfilter_xtables_heap_oob_write_priv_esc.rb	Apr 28, 2025

CVSS Scores

CVSS v3.1 8.3 High

CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H

CVSS v2.0 4.6 Medium

AV:L/AC:L/Au:N/C:P/I:P/A:P

Exploitation Status

Exploited in the wild

Recorded 2026-06-01 13:30:37 UTC · CISA

Proof of concept available

Recorded 2021-07-16 01:54:01 UTC · GitHub

Weaknesses (CWE)

CWE-787

Out-of-bounds Write

Scanner Integrations

Scanner	Reference	Detected
Metasploit	https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/linux/local/netfilter_xtables_heap_oob_write_priv_esc.rb	Apr 28, 2025

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

letsr00t/-2021-LOCALROOT-CVE-2021-22555

github · Created 2024-02-05 07:05:13 UTC · 0 stars

pashayogi/CVE-2021-22555

github · Created 2023-08-20 14:26:28 UTC · 0 stars

Linux Kernel 2.6.19 < 5.9 - 'Netfilter Local Privilege Escalation'

tukru/CVE-2021-22555

github · Created 2023-08-05 18:56:18 UTC · 3 stars

This repo hosts TUKRU's Linux Privilege Escalation exploit (CVE-2021-22555). It demonstrates gaining root privileges via a vulnerability. Tested on Ubuntu 5.8.0-48-generic and COS 5.4.89+. Use responsibly and ethically.

veritas501/CVE-2021-22555-PipeVersion

github · Created 2022-04-05 06:35:25 UTC · 36 stars

CVE-2021-22555 exploit rewritten with pipe primitive

xyjl-ly/CVE-2021-22555-Exploit

github · Created 2021-07-16 01:54:01 UTC · 10 stars

CVE-2021-22555 Exploit

netfilter_xtables_heap_oob_write_priv_esc

metasploit · Created Unknown

Metasploit module for CVE-2021-22555

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Confidence scoring, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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Pro API Example

GET /api/v2/pro/kevs/CVE-2021-22555

{
  "cve_id": "CVE-2021-22555",
  "title": "Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACE",
  "affected_vendor": "Linux",
  "affected_product": "Linux Kernel",
  "affected_versions": [
    { "vendor": "...", "product": "...", "status": "affected", "display_label": "..." }
  ],
  "confidence": "Confirmed",
  "cvss_score": 8.3,
  "epss_score": 0.78684,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "...": "Pro API fields" },
  "proof_of_concepts": [ "..." ],
  "scanner_integrations": [ "..." ]
}

The free JSON API returns basic KEV fields only. Confidence, telemetry, and artifact enrichment require Pro API access.

CVE-2021-22555

At a Glance

Affected Versions

CVE References

Recommended Actions

Known Exploited Vulnerability Sources

Scanner Artifacts

Virtual Patch

CVSS Scores

Exploitation Status

Weaknesses (CWE)

Scanner Integrations

Potential Proof of Concepts

Timeline

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