CVE-2026-57963
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedAn 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceThunderbird fails to properly sanitize HTML content in Matrix and XMPP chat messages, allowing remote attackers to inject arbitrary HTML, CSS, and phishing links into the chat UI. This enables manipulation of the application's visual presentation and potential credential theft through deceptive content.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 140.12.1< 152.0.1CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed Thunderbird versionIn Thunderbird, go to Help > About Thunderbird. On Windows, you can also check the executable properties, or run: thunderbird --versionAffected if The version displayed is below 140.12.1 or below 152.0.1 (note: 140.x and 152.x are separate release tracks)
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Verify if Matrix account is configuredIn Thunderbird, go to Settings > Account Settings and look for Matrix accounts listed under the Accounts sectionAffected if A Matrix account is present and the Thunderbird version is vulnerable (see step 1)
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Verify if XMPP account is configuredIn Thunderbird, go to Settings > Account Settings and look for Jabber/XMPP accounts listed under the Accounts sectionAffected if An XMPP account is present and the Thunderbird version is vulnerable (see step 1)
You are affected if your Thunderbird version is below 140.12.1 or below 152.0.1 AND you have at least one Matrix or XMPP account configured in Thunderbird.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped140.12.1152.0.1
Update Thunderbird to version 152.0.1 or 140.12.1 or later to patch the vulnerability. Organizations should deploy the updated version across all endpoints using Thunderbird for Matrix/XMPP communications.
Thunderbird 140.12.1 or Thunderbird 152.0.1
- Check current Thunderbird version: Help > About Thunderbird
- Download Thunderbird 140.12.1 or Thunderbird 152.0.1 from the official Mozilla Thunderbird website (www.mozilla.org)
- Close Thunderbird completely before installing the update
- Run the installer and follow the prompts to complete the upgrade
- Verify the upgrade was successful by checking Help > About Thunderbird shows the new version
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation1.0 h
- Implementation2.0 h
- Testing1.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-57963 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-57963 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data