Skip to main content
ExploitedIn CISA KEVFix available

CVE-2021-22555

Exploitation confirmed. First attested on 2025-10-04 by CISA-ADP, CISA KEV, GCVE · kevintel.

  • Published2021-07-07
  • Fixed in5.12 · 5.10.31 · 5.4.113 · 4.19.188 · 4.14.231 · 4.9.267
  • WeaknessCWE-787

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

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

Timeline

dates in UTC
  1. 2021-07-0712:15CVE publishedNVD
  2. 2021-07-15Exploit-DB entryExploit-DB
  3. 2025-10-0403:55Exploitation first reportedCISA-ADP
  4. 2025-10-0403:55SSVC exploitation set to activeCISA-ADP
  5. 2025-10-06Added to the CISA KEV catalogCISA KEV
  6. 2025-10-06Listed as exploited by GCVEGCVE

Observed activity

isMalicious corpus · updated 2026-11-03 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-22555?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-22555?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Linux linux kernel
BranchAffectedFixed in
5.x≥ 5.11, < 5.125.12
5.x≥ 5.5, < 5.10.315.10.31
5.4≥ 4.20, < 5.4.1135.4.113
4.x≥ 4.15, < 4.19.1884.19.188
4.x≥ 4.10, < 4.14.2314.14.231
4.x≥ 4.5, < 4.9.2674.9.267
4.4≥ 2.6.19, < 4.4.2674.4.267
Broadcom fabric operating system
BranchAffectedFixed in
—all versionsno fix published
Netapp aff 500f firmwareversion to verify
BranchAffectedFixed in
—all versionsno fix published

18 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Products declared by the CNA1 product

As Google, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • Linux Kernel
    Affected
    • = 2.6.19-rc1no fix statedcustom

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2022-01-06

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • :linux_kernel:Androidfrom :0 · fixed in :2021-10-05
  • kernelTuxCare:OracleLinux:6all versions · fixed in 2.6.32-754.35.2.el6and 6 other packages
  • kernelTuxCare:CentOS:6all versions · fixed in 2.6.32-754.35.6.el6and 9 other packages
  • kernelRocky Linux:8all versions · fixed in 0:4.18.0-305.12.1.el8_4
  • kernelRed Hat:rhel_tus:7.7::serverall versions · fixed in 0:3.10.0-1062.56.1.el7and 18 other packages
  • kernelRed Hat:rhel_tus:7.6::serverall versions · fixed in 0:3.10.0-957.84.1.el7and 17 other packages
  • kernelRed Hat:rhel_eus:8.2::baseosall versions · fixed in 0:4.18.0-193.64.1.el8_2and 32 other packages
  • kernelRed Hat:rhel_eus:8.1::baseosall versions · fixed in 0:4.18.0-147.52.1.el8_1and 32 other packages

272 more package ranges on OSV.dev

Vendor advisories

  • CVE-2021-22555 Red Hat Product Security1,259 products fixed · 16 known affected

    kernel: out-of-bounds write in xt_compat_target_from_user() in net/netfilter/x_tables.c

    kernel as a component of Red Hat Enterprise Linux 7 · kernel-abi-whitelists as a component of Red Hat Enterprise Linux 7 · kernel-alt.src as a component of Red Hat Enterprise Linux 7 · +13 more

  • RHSA-2025:17733 Red Hat Product Security56 products fixed

    Red Hat Security Advisory: kernel security update

  • RHSA-2021:3812 Red Hat Product Security96 products fixed

    Red Hat Security Advisory: kernel security update

  • RHSA-2021:3814 Red Hat Product Security50 products fixed

    Red Hat Security Advisory: kpatch-patch security update

  • RHSA-2021:3725 Red Hat Product Security24 products fixed

    Red Hat Security Advisory: kernel security and bug fix update

  • RHSA-2021:3523 Red Hat Product Security45 products fixed

    Red Hat Security Advisory: kpatch-patch security update

16 more advisories

Full record on NVD

Fix

  1. Update Linux linux kernel to 5.12 · 5.10.31 · 5.4.113 · 4.19.188 · 4.14.231 · 4.9.267 · 4.4.267
  2. CISA’s 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.due 2025-10-27
  3. Vendor fix Red Hat Product Security RHSA-2025:17733 · 56 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258 The system must be rebooted for this update to take effect.
  4. Vendor fix Red Hat Product Security RHSA-2021:3814 · 50 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/11258
  5. Vendor fix Red Hat Product Security RHSA-2021:3477 · 4 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://access.redhat.com/articles/2974891
  6. Workaround from the vendor Red Hat Product Security RHSA-2025:17733 · 56 productsThe mitigation for the Red Hat Enterprise Linux 8 is to disable unprivileged users from running unshare(CLONE_NEWUSER) or unshare(CLONE_NEWNET) that could be done with this command: echo 0 > /proc/sys/user/max_user_namespaces For making this change in configuration permanent. Note: User namespaces…

Advisories and patches

Detection

read 2026-11-03 22:42 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
EDB-50135
Exploit-DB
Proof-of-concept repositories
13 repositories, unverifiedJoneyJunior/cve-2021-22555xyjl-ly/CVE-2021-22555-Exploitcgwalters/container-cve-2021-22555daletoniris/CVE-2021-22555-esc-privveritas501/CVE-2021-22555-PipeVersion
PoC-in-GitHub
Metasploit modules
1 moduleexploit/linux/local/netfilter_xtables_heap_oob_write_priv_escrank: greatModule metadata: Metasploit Framework, © Rapid7, Inc., BSD-3-Clause.
Metasploit Framework

CISA Known Exploited Vulnerability

Date Added
2025-10-06
Patch Due Date
2025-10-27
Ransomware Use
Unknown
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.

Sources

  • CISA KEVKEV entry2025-10-06
  • ENISA EUVDexploitation2025-10-062025-10-06
  • GCVEexploitation2025-10-06
  • CISA-ADPSSVC decisionactive2025-10-04
  • OpenCVESSVC decisionactive—
  • CNACVSS 3.18.3known since 2026-10-23
  • NVDCVSS 3.17.8read 2026-10-23
  • NVDCVSS 2.04.6read 2026-10-23
  • CNAweakness (CWE)CWE-787known since 2026-10-23
  • NVDweakness (CWE)CWE-787read 2026-10-23
  • FIRST EPSSEPSS score78.7 %read 2026-11-03
  • PoC-in-GitHubproof of concept13read 2026-11-03
  • Exploit-DBdetectionread 2026-11-03
  • Metasploit FrameworkMetasploit modules1known since 2026-11-01
  • OSVaffected packages—

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Published
2021-07-07
Last Modified
2026-10-13
NVD status
Analyzed

Frequently asked questions

What is CVE-2021-22555?

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

Is CVE-2021-22555 actively exploited?

Yes. CVE-2021-22555 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, meaning it has been confirmed as actively exploited in the wild. CISA requires federal agencies to patch by 2025-10-27.

What is the CVSS score for CVE-2021-22555?

CVE-2021-22555 has a CVSS v3 base score of 7.8 (HIGH severity), with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

Running Linux kernel? Hear about its next vulnerability

Surveillance reads the versions in your stack — a domain, a lockfile or a list — checks each CVE against the ranges its sources publish, and alerts you when one you run is exploited or enters CISA KEV. A version it cannot read stays « version not verified ».

Get alerts for this productCISA KEV additions, October 2025Search CVEs

No credit card required · No monthly cap on website lookups · 250 API requests/month

Go further

Related vulnerabilities

Same product first, then the same vendor advisory and the same publication week.

Back to CVE Database

Sources for this record