CVE-2021-43529

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2023-02-17. NVD baseline CVSS 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Trending — 3 sources updated this week
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 0%CVSS: 9.8Exploit: NoneExposed: 0

A fix is available — apply it.

Thunderbird versions prior to 91.3.0 are vulnerable to the heap overflow described in CVE-2021-43527 when processing S/MIME messages. Thunderbird versions 91.3.0 and later will not call the vulnerable code when processing S/MIME messages that contain certificates with DER-encoded DSA or RSA-PSS signatures.

CVSS v3
9.8
EG Score
9.8(medium)
EG Risk
—
EPSS
37.9%
KEV
Not listed

Published

February 16, 2023

Last Modified

March 19, 2025

Advisory Details (1)

Auto-updated Jul 7, 2026
No patch confirmed yet.
generic

1738501 - (CVE-2021-43529) Automatic S/MIME cert import should use additional verification using mozilla::pkix

https://bugzilla.mozilla.org/show_bug.cgi?id=CVE-2021-43529

Vendor Advisories for CVE-2021-43529(1)

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

Patch Availability(4)

Vendor / EcosystemFixed in / PatchReleasedSource
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

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

(3)

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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Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-43529?
CVE-2021-43529 is a critical vulnerability published on February 16, 2023. Thunderbird versions prior to 91.3.0 are vulnerable to the heap overflow described in CVE-2021-43527 when processing S/MIME messages. Thunderbird versions 91.3.0 and later will not call the vulnerable code when processing S/MIME messages that contain certificates with DER-encoded DSA or RSA-PSS…
When was CVE-2021-43529 disclosed?
CVE-2021-43529 was first published in the National Vulnerability Database on February 16, 2023, with the most recent update on March 19, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-43529 actively exploited?
CVE-2021-43529 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 37.9% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-43529?
CVE-2021-43529 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-43529?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-43529, 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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