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CVE-2026-57963

MEDIUM 6.5

Published 2026-07-01 · Last modified 2026-07-01

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.

NO EXPLOITATION SIGNALS

No known exploitation, public exploit, or elevated probability at this time. Track for changes.

Exploitation likelihood

0.1%chance of exploitation in 30 days · 4th percentile

○ In CISA KEV ○ Public exploit / PoC

Impact if exploited

6.5CVSS 3.1 · MEDIUM

  • ConfidentialityLow
  • IntegrityLow
  • AvailabilityNone

What an attacker needs

  • ✓Access: Reachable over the network — no local access needed
  • ✓Privileges: No account or privileges required
  • ✓User interaction: No user interaction needed
  • ✓Complexity: No special conditions — reliably repeatable

✓ lowers the bar for an attacker · ⚠ raises it

Affected

Vendors Mozilla

Products Thunderbird

Weakness (CWE)

  • CWE-79: Cross-site scripting (XSS)

CVSS vector

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

References

Technical & other

Sources: NVD · CVE.org · EPSS