Vulnerability details

CVE-2026-84639

Uninitialized memory in MIME parsing

CVSS 3.1

9.1Critical

Official 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.

CVSS scores

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

Affected products

Vendor	Product	Versions	Source
No product information recorded.

References and advisories

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Details

Published: 2026-09-02
Last updated: 2026-09-17
State: Published
Assigner (CNA): mozilla

Exploit prediction (EPSS)

0.32%

Probability of exploitation in 30 days

25.4%

Percentile (among all CVEs)

SSVC assessment (CISA)

Automatable: Yes
Exploitation: None
Technical impact: Partial

Weaknesses (CWE)

CWE-457
Use of Uninitialized Variable