Is CVE-2026-57963 in the CISA KEV catalog?

No. CVE-2026-57963 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-57963?

CVE-2026-57963 has a CVSS v3 base score of 6.5 (MEDIUM).

How do I fix or mitigate CVE-2026-57963?

No published fix for CVE-2026-57963 has been found yet. Check the linked vendor advisories for guidance as it becomes available.

CVE & CISA-KEV Catalog

CVE-2026-57963

MEDIUM

6.5

CVSS v3

NVD

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.

CWE-79Cross-Site Scripting (XSS)

How to fix

No published remediation has been found for this vulnerability's affected products yet.

Mitigation guidance may be in the linked vendor advisories in the References section below.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityLow

IntegrityLow

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Exploit Intelligence

EPSS data unavailable for this CVE.

References

Other references3

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Markdown

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HTML

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-07-01.