CVE-2026-4371

Description

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.

CVSS Metrics

• v3.1•HIGH•Score: 7.4CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H

EPSS Trends

Current EPSS score: 0.06%• Percentile: 20%

Techniques & Countermeasures

• CWE-126•Buffer Over-read

  The product reads from a buffer using buffer access mechanisms such as indexes or pointers that reference memory locations after the targeted buffer.

Affected Systems

• mozilla•thunderbird

  ≥ unspecified, < 149 | ≥ unspecified, < 140.9 | < 140.9.0 | < 149.0

References (3)

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