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CVE-2026-57963

Medium

Description

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.

SeverityMedium
CVSS6.5
Exploit probability—
ProductMozilla Thunderbird
PublishedJul 1, 2026
First seenJul 1, 2026
Weakness typeCWE-79Cross-site scripting (XSS)

How to fix

Update
  • mozilla thunderbird140.12.1, 152.0.1 or later

Affected products

ProductAffected versionsFixed in
mozilla thunderbirdv < 140.12.1, v < 152.0.1140.12.1, 152.0.1

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