CVE-2026-84640
highA maliciously constructed mail header could lead to a one byte read past the end of a buffer.
Vendor / product: Mozilla — thunderbird
A maliciously constructed mail header could lead to a one byte read past the end of a buffer. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.
CVSS
7.5
7.5 (CVSS v3.1)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N Severity source: NVD CVSS v3.1 (134c704f-9b21-4f2e-91b3-4a467353bcc0)
Timeline (UTC)
Published: 2026-09-01 22:17
Modified: 2026-09-03 19:01
NVD status: Analyzed
Last synced 1 day ago
Verified against the source API 2026-10-27 06:50 UTC
Exploitation
Not listed in CISA KEV (as of last catalog sync)
Absence from KEV does not mean a CVE is not exploited. Exploitation status: unknown (no authoritative evidence in our sources).
Affected products
mozilla / thunderbird <140.15.0, ≥141.0 <153.2.0, ≥154.0 <155.0
Weakness classification (CWE)
Source: NVD / CISA. “NVD-CWE-Other” and “NVD-CWE-noinfo” mean NVD could not assign a specific weakness.
Mitigation & advisories
Vendor advisory: https://www.mozilla.org/security/advisories/mfsa2026-86/
Vendor advisory: https://www.mozilla.org/security/advisories/mfsa2026-87/
Vendor advisory: https://www.mozilla.org/security/advisories/mfsa2026-88/
References
- https://bugzilla.mozilla.org/show_bug.cgi?id=2063964 security@mozilla.org
- https://www.mozilla.org/security/advisories/mfsa2026-86/ security@mozilla.org
- https://www.mozilla.org/security/advisories/mfsa2026-87/ security@mozilla.org
- https://www.mozilla.org/security/advisories/mfsa2026-88/ security@mozilla.org
Data sources
NVD CVE API 2.0 — fetched 2026-10-27 06:50 UTC · record ↗