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.
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.003 (18.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 19th percentile — 18.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000
Affected products
- Mozilla Thunderbird — versions 140.13, 153
Weakness classification (CWE)
References
- bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
- www.mozilla.org/security/advisories/mfsa2026-71/ (Vendor Advisory)
- www.mozilla.org/security/advisories/mfsa2026-72/ (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.