CVE-2026-57963

EUVD-2026-40862
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.
Cross-site Scripting
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
NISTPrimary
6.5 MEDIUM
NETWORK
LOW
NONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Awaiting analysis
This vulnerability is currently awaiting analysis.
Base Score
CVSS 3.x
EPSS Score
Percentile: 3%
Common Weakness Enumeration
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/