CVE-2026-57963: Mozilla Thunderbird

Medium severity, CVSS 6.5. EPSS: 0.3% chance of exploitation in the next 30 days.

An attacker who can send HTML chat messages (via Matrix or XMPP) can inject arbitrary styled content, phishing links, and CSS that manipulates the chat UI. This vulnerability was fixed in Thunderbird 152.0.1 and Thunderbird 140.12.1.

Affected products

• Mozilla Thunderbird: before 140.12.1 (fixed in 140.12.1); before 152.0.1 (fixed in 152.0.1)

Published 2026-07-01. Last modified 2026-07-06.