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
Base Score
CVSS 3.x
EPSS Score
Percentile: 9.09%
Affected Products (NVD)
VendorProductVersion
mozillathunderbird_esr
𝑥
< 140.12.1
mozillathunderbird
𝑥
< 152.0.1
𝑥
= Vulnerable software versions
Debian logo
Debian Releases
Debian Product
Codename
thunderbird
bookworm
vulnerable
bookworm (security)
1:140.13.0esr-2~deb12u1
fixed
bullseye
vulnerable
bullseye (security)
1:140.13.0esr-2~deb11u1
fixed
forky
vulnerable
sid
1:140.13.0esr-2
fixed
trixie
vulnerable
trixie (security)
1:140.13.0esr-2~deb13u1
fixed
Ubuntu logo
Ubuntu Releases
Ubuntu Product
Codename
thunderbird
jammy
needs-triage
noble
needs-triage
questing
ignored
resolute
needs-triage
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/