CVE-2026-84639

Uninitialized memory in MIME parsing

State: Published
Severity: 9.1 Critical
Published: Sep 1, 2026
Updated: Sep 17, 2026
Reserved: Sep 1, 2026

Description

Triggering an error condition in certain MIME bodies would cause uninitialized memory to be used. This vulnerability was fixed in Thunderbird 155, Thunderbird 140.15, and Thunderbird 153.2.

Scores

CVSS	Score	Vector	Source
3.1	9.1 Critical	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H	CISA-ADP

Weaknesses

CWE-457 Use of Uninitialized Variable

Affected Products

Product	Versions
ThunderbirdMozilla	140.15 through 140.Not affected 153.2 through 153.Not affected 155 and laterNot affected

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2061087
https://www.mozilla.org/security/advisories/mfsa2026-86/
https://www.mozilla.org/security/advisories/mfsa2026-87/
https://www.mozilla.org/security/advisories/mfsa2026-88/

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