CVE-2021-4138

MEDIUMNVD 5.35.3—

5.3

Improved Host header checks to reject requests not sent to a well-known local hostname or IP, or the server-specified hostname.

CVSS v3: 5.3
EG Score: 5.3(medium)
EPSS: 41.7%
KEV: Not listed

Published

May 2, 2022

Last Modified

November 21, 2024

References (4)

security@mozillahttps://bugzilla.mozilla.org/show_bug.cgi?id=1652612
security@mozillahttps://github.com/mozilla/geckodriver/releases/tag/v0.30.0
af854a3a-2127-422b-91ae-364da2661108https://bugzilla.mozilla.org/show_bug.cgi?id=1652612
af854a3a-2127-422b-91ae-364da2661108https://github.com/mozilla/geckodriver/releases/tag/v0.30.0

Data Freshness Timeline

(refreshed 11× in last 7d / 20× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

2026-06-08 14:15 UTCEPSS rescore
2026-06-08 14:15 UTCEPSS rescore
2026-06-08 14:15 UTCEPSS rescore
2026-06-07 15:23 UTCEPSS rescore
2026-06-07 15:23 UTCEPSS rescore
2026-06-06 13:46 UTCEPSS rescore
2026-06-06 13:46 UTCEPSS rescore
2026-06-05 22:45 UTCEPSS rescore
2026-06-05 22:45 UTCEPSS rescore
2026-06-05 06:09 UTCEPSS rescore
2026-06-05 06:09 UTCEPSS rescore
2026-06-02 20:11 UTCEPSS rescore
2026-06-02 20:11 UTCEPSS rescore
2026-06-01 13:50 UTCEPSS rescore
2026-06-01 13:50 UTCEPSS rescore
2026-05-31 22:29 UTCEPSS rescore
2026-05-31 00:15 UTCEPSS rescore
2026-05-31 00:15 UTCEPSS rescore
2026-05-29 13:42 UTCEPSS rescore
2026-05-28 13:43 UTCEPSS rescore

Frequently asked(5)

What is CVE-2021-4138?

CVE-2021-4138 is a medium vulnerability published on May 2, 2022. Improved Host header checks to reject requests not sent to a well-known local hostname or IP, or the server-specified hostname.

When was CVE-2021-4138 disclosed?

CVE-2021-4138 was first published in the National Vulnerability Database on May 2, 2022, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-4138 actively exploited?

CVE-2021-4138 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 41.7% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2021-4138?

CVE-2021-4138 has a CVSS v3 base score of 5.3 (NVD).

How do I remediate CVE-2021-4138?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-4138, 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.

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CVE-2021-4138

📅 Published

🔄 Last Modified

🔗 References (4)