CVE-2026-84639: critical vulnerability in Mozilla Thunderbird
Uninitialized memory in MIME parsing
Published · Updated
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28Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 9.1epss 0.3%
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:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H
Affected products
Mozilla · ThunderbirdRelated CVEs — Mozilla Thunderbird
In the same product, most dangerous first.