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CVE record · CVE-2026-84143

Internally found bugs fixed in Thunderbird 155, Thunderbird ESR 153.2 and Thunderbird ESR 140.15

CVSS 9.8 CriticalCriticalEPSS 0.0038 · 31st percentile

Critical, because:

  • CVSS score 9.8: 9.0 or more.

How we decide what’s critical

Published by the CVE Program (CNA: mozilla) at 1 Sept 2026, 12:19 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it.

Affected products, as the CNA wrote them
VendorProductVersions
Mozilla Firefox
  • unaffected 140.15 to 140.*, inclusive rpm
  • unaffected 153.2 to 153.*, inclusive rpm
  • unaffected 155 to *, inclusive rpm
Mozilla Thunderbird
  • unaffected 140.15 to 140.*, inclusive rpm
  • unaffected 153.2 to 153.*, inclusive rpm
  • unaffected 155 to *, inclusive rpm
Identifiers
CVE-2026-84143
CNA
mozilla
Weakness (CWE)
CWE-200
Tags
Published
1 Sept 2026
Updated
3 Sept 2026

Not analysed yet

We haven’t published our own analysis of this CVE. If a person reviews it, this page will say what’s affected and what has to be true for it to matter.

Severity and exploitation

ScoreRatingCVSSVectorSource
9.8 Critical 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H ADP (CISA-ADP)
  • CISA KEV Not listed.
  • EPSS 0.0038, the 31st percentile, on 9 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

This record came from the full history of the CVE Program, published 1 Sept 2026. New records show when each source confirmed them.

Sources

References from the CNA

Facts on this page come from the CVE List as the CNA published them, with CVSS from the sources named above, CISA KEV and FIRST EPSS. Vendors, products and versions are shown as the CNA wrote them. We don’t reproduce the CVE’s description.