CVE-2026-14899
High
Description
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.
SeverityHigh
CVSS7.5
Exploit probability—
Product
Mozilla Thunderbird
PublishedJul 22, 2026
First seenJul 22, 2026
Weakness typeCWE-193CWE-193
How to fix
Update
- mozilla thunderbird140.13.0 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| mozilla thunderbird | v < 140.13.0 | 140.13.0 |
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