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vulnerability

CVE-2021-22555

8.3
High
KEV · Exploited in wildEPSS 79%Patch available

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

exploited
Yes, in CISA KEV since 6 Oct 2025fix by 27 Oct 2025 (CISA deadline for US federal agencies)public exploit code
fix
Patch available see the advisory in the references
likelihood
EPSS 78.7%
Published 7 Jul 2021Analysed here 2 Nov 2026CVSS scored by the publisher (CNA)

do firstApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

triage
server-sideruntimeWAF can block: noAV · adjacent networkCWE-787· Out-of-Bounds Write

Can a WAF block it? No. The vulnerability involves a heap out-of-bounds write in the Linux kernel's netfilter component, which requires local or user namespace access to exploit. It is not triggered via HTTP requests, so a web application firewall cannot detect or block it.

Also consider: patch

Based on an AI reading of the CVE description, and no vendor rule found yet. We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.

cvss vector
attack vectoradjacentattack complexityhighprivileges requirednoneuser interactionnonescopechangedconfidentialityhighintegrityhighavailabilityhigh
CVSS 3.1 · CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
common questions

Is CVE-2021-22555 being exploited?

Yes. CVE-2021-22555 appears in CISA's Known Exploited Vulnerabilities catalog, which means exploitation in the wild has been confirmed and reported. Treat it as active rather than theoretical, and patch it ahead of higher-scoring vulnerabilities that carry no exploitation evidence.

How severe is CVE-2021-22555?

CVE-2021-22555 is rated High with a CVSS score of 8.3. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.

Is there a patch for CVE-2021-22555?

Yes. A fix has been recorded for CVE-2021-22555. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.

What does CVE-2021-22555 affect?

CVE-2021-22555 affects netapp:c400_firmware, netapp:c250_firmware, netapp:h410c_firmware, netapp:h300s_firmware, and 17 further products or versions. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.

Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.

executive summary
technical analysis
affected
netapp:c400_firmwarenetapp:c250_firmwarenetapp:h410c_firmwarenetapp:h300s_firmwarenetapp:h500s_firmwarenetapp:h700s_firmwarenetapp:h410s_firmwarelinux:linux_kernelbroadcom:fabric_operating_systemnetapp:fas_8300_firmwarenetapp:fas_8700_firmwarenetapp:aff_a400_firmwarenetapp:aff_a250_firmwarenetapp:aff_500f_firmwarenetapp:h610c_firmwarenetapp:h610s_firmwarenetapp:h615c_firmwarenetapp:cloud_backupnetapp:hci_management_nodenetapp:solidfirenetapp:solidfire_baseboard_management_controller
affected versions
Linux Kernel
  • affected>= 2.6.19-rc1 and < unspecified

As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.

public exploits

Public exploit code: 1 on Exploit-DB · 1 Metasploit module · 13 GitHub proofs of concept

Exploit-DB
GitHub proofs of concept
+9 more repositories

Listed so you can judge urgency, not as a recommendation to run anything. GitHub “proofs of concept” are unvetted: some are fake or carry malware. Exploit-DB marks the entries its staff verified.

cisa ssvc

exploitation
active
automatable
no
technical impact
total

Assessed by CISA 4 Oct 2025 (SSVC 2.0.3).

timeline

  1. 7 Jul 2021Published
  2. 15 Jul 2021First public exploit or proof of concept · 7 days later
  3. 4 Oct 2025CISA SSVC assessment: exploitation active · 1,542 days (about 4 years) later
  4. 6 Oct 2025Added to CISA KEV (exploited in the wild) · 2 days later
  5. 27 Oct 2025CISA remediation due date (US federal agencies) · 21 days later
  6. 30 Dec 2025CVE record last updated · 65 days (about 2 months) later
  7. 2 Nov 2026Analysed by vulneraibility.com · 307 days (about 10 months) later

also known as

GHSA-xxx5-8mvq-3528
how to fix
Remediation steps are tailored for users whose stack is affected. Add this technology to your stack to see the fix checklist.
references
NVDCVE.orgCVE DetailsSource
10 references in the CVE record: 10 links
Show 2 more
  • Linkpacketstormsecurity.com /files/165477/Kernel-Live-Patch-Security-Notice-LSN-0083-1.html
  • Linkcisa.gov /known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-22555

sources

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