CVE-2018-18509: Mozilla Thunderbird

Medium severity, CVSS 5.3. EPSS: 1.7% chance of exploitation in the next 30 days.

A flaw during verification of certain S/MIME signatures causes emails to be shown in Thunderbird as having a valid digital signature, even if the shown message contents aren't covered by the signature. The flaw allows an attacker to reuse a valid S/MIME signature to craft an email message with arbitrary content. This vulnerability affects Thunderbird < 60.5.1.

Affected products

• Mozilla Thunderbird: before 60.5.1 (fixed in 60.5.1)

Published 2019-04-26. Last modified 2026-06-17.