CVE-2021-43537

HIGHNVD 8.88.8—
EchelonGraph scoreMEDIUM confidence

Score 8.8 from GitHub Security Advisory (severity: HIGH) published 2021-12-09. NVD baseline CVSS 8.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Trending — 3 sources updated this week
8.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 2%CVSS: 8.8Exploit: NoneExposed: 0

A fix is available — apply it.

An incorrect type conversion of sizes from 64bit to 32bit integers allowed an attacker to corrupt memory leading to a potentially exploitable crash. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.

CVSS v3
8.8
EG Score
8.8(medium)
EG Risk
—
EPSS
78.9%
KEV
Not listed

Published

December 8, 2021

Last Modified

November 21, 2024

References (20)

Vendor Advisories for CVE-2021-43537(2)

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

Patch Availability(13)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuthunderbird-locale-id (1:91.5.0+build1-0ubuntu0.21.10.1) @ impish2026-05-26ubuntu
ubuntufirefox-locale-ast (95.0+build1-0ubuntu0.18.04.1) @ bionic2026-05-26ubuntu
ubuntuthunderbird-locale-id (1:91.5.0+build1-0ubuntu0.20.04.1) @ focal2026-05-26ubuntu
redhatthunderbird-0:91.4.0-3.el7_92021-12-09redhat
redhatthunderbird-0:91.4.0-2.el8_42021-12-09redhat
redhatthunderbird-0:91.4.0-2.el8_52021-12-09redhat
redhatthunderbird-0:91.4.0-2.el8_12021-12-09redhat
redhatthunderbird-0:91.4.0-2.el8_22021-12-09redhat
redhatfirefox-0:91.4.0-1.el8_12021-12-08redhat
redhatfirefox-0:91.4.0-1.el8_42021-12-08redhat
redhatfirefox-0:91.4.0-1.el7_92021-12-08redhat
redhatfirefox-0:91.4.0-1.el8_52021-12-08redhat
redhatfirefox-0:91.4.0-1.el8_22021-12-08redhat

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

(11)

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 12× in last 7d / 50× 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 107 total refreshes for this CVE.

  1. 2026-07-22 22:51 UTCEG score recompute
  2. 2026-07-22 14:06 UTCEPSS rescore
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Frequently asked(5)

What is CVE-2021-43537?
CVE-2021-43537 is a high vulnerability published on December 8, 2021. An incorrect type conversion of sizes from 64bit to 32bit integers allowed an attacker to corrupt memory leading to a potentially exploitable crash. This vulnerability affects Thunderbird < 91.4.0, Firefox ESR < 91.4.0, and Firefox < 95.
When was CVE-2021-43537 disclosed?
CVE-2021-43537 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-2021-43537 actively exploited?
CVE-2021-43537 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 78.9% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-43537?
CVE-2021-43537 has a CVSS v3 base score of 8.8 (NVD).
How do I remediate CVE-2021-43537?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-43537, 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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