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VulnerabilityPublished

CVE-2026-57963: Mozilla Thunderbird · Cross-site Scripting

Affects Mozilla ThunderbirdSource CVE Database V5

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Not known to be exploited · CVSS 6.5 Medium · patch available : update Mozilla Thunderbird when convenient.

Data as of 12 Nov 2026, 23:24 UTC

CVSS 3.1 base score
6.5Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 23% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 1 Jul 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 13 Nov 2026.

What to do

Affected software

ProductAffectedFixed in
Mozilla ThunderbirdAffected
  • <140.12.1
  • <152.0.1
Fixed in
  • 140.12.1
  • 152.0.1

AI-suggested

This vulnerability has been fixed in Mozilla Thunderbird versions 140.12.1 and 152.0.1. Users and administrators should upgrade affected Thunderbird installations to at least these versions to remediate the issue. Since the vendor advisory confirms the fix, no additional mitigation steps are required beyond applying the official update.

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.

References

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