CVE-2021-4128

MEDIUMNVD 6.56.5—Elevated

6.5

When transitioning in and out of fullscreen mode, a graphics object was not correctly protected; resulting in memory corruption and a potentially exploitable crash.*This bug only affects Firefox on MacOS. Other operating systems are unaffected.*. This vulnerability affects Firefox < 95.

CVSS v3: 6.5
EG Score: 6.5(medium)
EPSS: 41.5%
KEV: Not listed

Published

December 22, 2022

Last Modified

April 16, 2025

References (4)

security@mozillahttps://bugzilla.mozilla.org/show_bug.cgi?id=1735852
security@mozillahttps://www.mozilla.org/security/advisories/mfsa2021-52/
af854a3a-2127-422b-91ae-364da2661108https://bugzilla.mozilla.org/show_bug.cgi?id=1735852
af854a3a-2127-422b-91ae-364da2661108https://www.mozilla.org/security/advisories/mfsa2021-52/

Weakness Classification(1)

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

CWE-416Use After Free

Data Freshness Timeline

(refreshed 12× in last 7d / 49× 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.

2026-06-21 01:58 UTCEPSS rescore
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2026-06-19 19:24 UTCEPSS rescore
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2026-06-18 17:51 UTCEPSS rescore
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2026-06-16 17:51 UTCEPSS rescore
2026-06-15 17:46 UTCEPSS rescore
2026-06-14 23:15 UTCEPSS rescore
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2026-06-13 22:58 UTCEPSS rescore
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2026-06-12 23:10 UTCEPSS rescore
2026-06-11 13:58 UTCEPSS rescore
2026-06-10 22:16 UTCEPSS rescore
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2026-06-08 14:15 UTCEPSS rescore
2026-06-08 14:15 UTCEPSS rescore
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2026-06-07 15:23 UTCEPSS rescore
2026-06-07 15:23 UTCEPSS rescore
2026-06-06 13:46 UTCEPSS rescore
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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
2026-06-04 13:11 UTCEPSS rescore
2026-06-04 13:10 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
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2026-05-29 13:42 UTCEPSS rescore
2026-05-28 13:43 UTCEPSS rescore
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2026-05-27 13:39 UTCEPSS rescore
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2026-05-26 13:43 UTCEPSS rescore
2026-05-26 13:42 UTCEPSS rescore
2026-05-26 07:17 UTCEPSS rescore
2026-05-26 07:17 UTCEPSS rescore
2026-05-25 10:03 UTCEG score recompute
2026-05-25 10:03 UTCGHSA enrichment

Frequently asked(5)

What is CVE-2021-4128?

CVE-2021-4128 is a medium vulnerability published on December 22, 2022. When transitioning in and out of fullscreen mode, a graphics object was not correctly protected; resulting in memory corruption and a potentially exploitable crash.<br>This bug only affects Firefox on MacOS. Other operating systems are unaffected.. This vulnerability affects Firefox < 95.

When was CVE-2021-4128 disclosed?

CVE-2021-4128 was first published in the National Vulnerability Database on December 22, 2022, with the most recent update on April 16, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-4128 actively exploited?

CVE-2021-4128 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 41.5% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2021-4128?

CVE-2021-4128 has a CVSS v3 base score of 6.5 (NVD).

How do I remediate CVE-2021-4128?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-4128, 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-2021-4128

📅 Published

🔄 Last Modified

🔗 References (4)

Weakness Classification(1)

Data Freshness Timeline

❓ Frequently asked(5)

Dependency Blast Radius

Is Your Infrastructure Affected by CVE-2021-4128?

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References (4)

Frequently asked(5)

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