Thunderbird MIME header OBO read before 153
CVE-2026-14899 Published on July 22, 2026
Off-by-one out of bounds read in MIME header parser for forwarding
The code to parse MIME headers for display when forwarding a message (if the setting to view all headers was enabled) had an off-by-one error, allowing a single byte to be read from the memory after the buffer for the headers, and potentially crashing Thunderbird. This vulnerability was fixed in Thunderbird 153 and Thunderbird 140.13.
Products Associated with CVE-2026-14899
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Affected Versions
Mozilla Thunderbird:- Version 140.13, <= 140.* is unaffected.
- Version 153, <= * is unaffected.