CVE-2021-38506

MEDIUMNVD 4.34.3—
EchelonGraph scoreMEDIUM confidence

Score 4.3 from GitHub Security Advisory published 2021-12-09. NVD baseline CVSS 4.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Trending — 3 sources updated this week
4.3
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 1%CVSS: 4.3Exploit: NoneExposed: 0

A fix is available — apply it.

Through a series of navigations, Firefox could have entered fullscreen mode without notification or warning to the user. This could lead to spoofing attacks on the browser UI including phishing. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.

CVSS v3
4.3
EG Score
4.3(medium)
EG Risk
24(Track)
EG Risk 24/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity43% × 45%
Exploitation1% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS
70.8%
KEV
Not listed

Published

December 8, 2021

Last Modified

November 21, 2024

References (20)

Vendor Advisories for CVE-2021-38506(2)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(11)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuthunderbird-locale-id (1:91.5.0+build1-0ubuntu0.20.04.1) @ focal2026-05-26ubuntu
ubuntuthunderbird-locale-id (1:91.3.1+build1-0ubuntu0.21.10.1) @ impish2026-05-26ubuntu
ubuntufirefox-locale-ast (94.0+build3-0ubuntu0.21.10.1) @ impish2026-05-26ubuntu
redhatfirefox-0:91.3.0-1.el8_22021-11-10redhat
redhatfirefox-0:91.3.0-1.el8_12021-11-10redhat
redhatthunderbird-0:91.3.0-2.el7_92021-11-04redhat
redhatthunderbird-0:91.3.0-2.el8_42021-11-04redhat
redhatthunderbird-0:91.3.0-2.el8_12021-11-04redhat
redhatthunderbird-0:91.3.0-2.el8_22021-11-04redhat
redhatfirefox-0:91.3.0-1.el8_42021-11-03redhat
redhatfirefox-0:91.3.0-1.el7_92021-11-03redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(1)

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

Additional Vendor Advisories

(9)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 17× 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.

Showing the most recent 100 of 106 total refreshes for this CVE.

  1. 2026-07-23 14:16 UTCEPSS rescore
  2. 2026-07-23 14:16 UTCEPSS rescore
  3. 2026-07-23 02:03 UTCEG score recompute
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  43. 2026-06-12 15:10 UTCOSV refresh
  44. 2026-06-11 13:58 UTCEPSS rescore
  45. 2026-06-10 22:16 UTCEPSS rescore
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Frequently asked(5)

What is CVE-2021-38506?
CVE-2021-38506 is a medium vulnerability published on December 8, 2021. Through a series of navigations, Firefox could have entered fullscreen mode without notification or warning to the user. This could lead to spoofing attacks on the browser UI including phishing. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.
When was CVE-2021-38506 disclosed?
CVE-2021-38506 was first published in the National Vulnerability Database on December 8, 2021, 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-2021-38506 actively exploited?
CVE-2021-38506 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 70.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-38506?
CVE-2021-38506 has a CVSS v3 base score of 4.3 (NVD).
How do I remediate CVE-2021-38506?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-38506, 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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