CVE-2026-4371

Summary

A malicious mail server could send malformed strings with negative lengths, causing the parser to read memory outside the buffer. If a mail server or connection to a mail server were compromised, an attacker could cause the parser to malfunction, potentially crashing Thunderbird or leaking sensitive data. This vulnerability was fixed in Thunderbird 149 and Thunderbird 140.9.

Impact & exploitability

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H

Affected products we track (1)

Recommendation

Apply the vendor fix promptly. Open any affected product above for its exact safe version.

Additional information

• NVD record
• https://www.mozilla.org/security/advisories/mfsa2026-23/Advisory
• https://www.mozilla.org/security/advisories/mfsa2026-24/Advisory
• https://bugzilla.mozilla.org/show_bug.cgi?id=2023493