CVE-2021-4226

CRITICALNVD 9.89.8—Elevated

9.8

RSFirewall tries to identify the original IP address by looking at different HTTP headers. A bypass is possible due to the way it is implemented.

CVSS v3: 9.8
EG Score: 9.8(medium)
EPSS: 33.5%
KEV: Not listed

Published

December 15, 2022

Last Modified

May 27, 2025

References (2)

contact@wpscanhttps://wpscan.com/vulnerability/c0ed80c8-ebbf-4ed9-b02f-31660097c352
af854a3a-2127-422b-91ae-364da2661108https://wpscan.com/vulnerability/c0ed80c8-ebbf-4ed9-b02f-31660097c352

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 10× in last 7d / 18× in last 30d)

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

2026-06-02 20:11 UTCepss_batch
2026-06-02 20:11 UTCepss_batch
2026-06-01 13:50 UTCepss_batch
2026-06-01 13:50 UTCepss_batch
2026-05-31 22:29 UTCepss_batch
2026-05-31 00:15 UTCepss_batch
2026-05-31 00:15 UTCepss_batch
2026-05-29 13:42 UTCepss_batch
2026-05-28 13:43 UTCepss_batch
2026-05-28 13:43 UTCepss_batch
2026-05-27 13:39 UTCepss_batch
2026-05-27 13:39 UTCepss_batch
2026-05-26 13:43 UTCepss_batch
2026-05-26 13:42 UTCepss_batch
2026-05-26 07:17 UTCepss_batch
2026-05-26 07:17 UTCepss_batch
2026-05-25 10:33 UTCEG score recompute
2026-05-25 10:33 UTCGHSA enrichment

Frequently asked(5)

What is CVE-2021-4226?

CVE-2021-4226 is a critical vulnerability published on December 15, 2022. RSFirewall tries to identify the original IP address by looking at different HTTP headers. A bypass is possible due to the way it is implemented.

When was CVE-2021-4226 disclosed?

CVE-2021-4226 was first published in the National Vulnerability Database on December 15, 2022, with the most recent update on May 27, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-4226 actively exploited?

CVE-2021-4226 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 33.5% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2021-4226?

CVE-2021-4226 has a CVSS v3 base score of 9.8 (NVD).

How do I remediate CVE-2021-4226?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-4226, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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CVE-2021-4226

📅 Published

🔄 Last Modified

🔗 References (2)

Weakness Classification(2)

Data Freshness Timeline

❓ Frequently asked(5)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-4226?

🔗 Related CVEs(same CWE)

Same CWE

Published

Last Modified

References (2)

Frequently asked(5)

Related CVEs(same CWE)