CVE-2025-3523: Mozilla Thunderbird

Medium severity, CVSS 6.4. EPSS: 0.3% chance of exploitation in the next 30 days.

When an email contains multiple attachments with external links via the X-Mozilla-External-Attachment-URL header, only the last link is shown when hovering over any attachment. Although the correct link is used on click, the misleading hover text could trick users into downloading content from untrusted sources. This vulnerability was fixed in Thunderbird 137.0.2 and Thunderbird 128.9.2.

Affected products

• Mozilla Thunderbird: before 128.9.2 (fixed in 128.9.2); from 129.0, before 137.0.2 (fixed in 137.0.2)

Published 2025-04-15. Last modified 2026-06-17.