CVE-2026-57963: Chat UI manipulation by injection

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-07-01 · updated 2026-10-25
Weakness: CWE-79

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.

Affected products

Mozilla Thunderbird: before 140.12.1; before 152.0.1 — fixed in 140.12.1, 152.0.1

How to fix

Upgrade to a fixed version: Mozilla Thunderbird 140.12.1, 152.0.1. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=2042910
https://www.mozilla.org/security/advisories/mfsa2026-63/
https://www.mozilla.org/security/advisories/mfsa2026-64/

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