Mail Header Buffer Overread (Read Past End) in Thunderbird <155 (fixed in 155)
CVE-2026-84640 Published on September 1, 2026
One byte overflow read in mail parser
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.
Products Associated with CVE-2026-84640
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Affected Versions
Mozilla Thunderbird:- Version 140.15, <= 140.* is unaffected.
- Version 153.2, <= 153.* is unaffected.
- Version 155, <= * is unaffected.