Vulnerability in Mozilla Thunderbird
CVE-2026-14899
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.
EPSS: 0.003 (19.4th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.
Affected products
- Mozilla Thunderbird — versions 140.13, 153
Weakness classification (CWE)
References
- security@mozilla.org (Permissions Required)
- security@mozilla.org (Vendor Advisory)
- security@mozilla.org (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-14899?
- CVE-2026-14899 is a high-severity vulnerability in Mozilla Thunderbird, classified under Off-by-one Error. CVSS score: 7.5/10. Published 2026-07-22.
- How severe is CVE-2026-14899?
- High severity. CVSS v3 base score is 7.5 out of 10.