HTML Injection via Matrix/XMPP in Thunderbird <152.0.1 & <140.12.1
CVE-2026-57963 Published on July 1, 2026
Chat UI manipulation by injection
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.
Vulnerability Analysis
CVE-2026-57963 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality and integrity, and no impact on availability.
Weakness Type
What is a XSS Vulnerability?
The software does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
CVE-2026-57963 has been classified to as a XSS vulnerability or weakness.
Products Associated with CVE-2026-57963
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Affected Versions
Mozilla Thunderbird:- Version 140.12.1, <= 140.* is unaffected.
- Version 152.0.1, <= * is unaffected.