Medium 6.5Published Jul 1, 2026

CVE-2026-57963An 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.

Updated under an hour ago (2026-10-19 09:10 UTC)

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It affects mozilla thunderbird. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

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.

CVSS: 6.5 MEDIUM (v3.1, NVD)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Weakness (CWE): CWE-79
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: Not given
NVD analysis: Analyzed
Record last updated: Jul 6, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

mozilla thunderbird mozilla:thunderbird	before 140.12.1; before 152.0.1	NVD

References

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

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.