CVE-2025-3932
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 · uneditedIt was possible to craft an email that showed a tracking link as an attachment. If the user attempted to open the attachment, Thunderbird automatically accessed the link. The configuration to block remote content did not prevent that. Thunderbird has been fixed to no longer allow access to web pages listed in the X-Mozilla-External-Attachment-URL header of an email. This vulnerability was fixed in Thunderbird 128.10.1 and Thunderbird 138.0.1.
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 automatically accessed tracking URLs specified in the X-Mozilla-External-Attachment-URL header when users attempted to open attachments, bypassing the remote content blocking configuration. This allowed email senders to detect when recipients opened emails by embedding tracking links as attachments.
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< 128.10.1>= 129.0, < 138.0.1CVSS 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
- Required
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/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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Determine installed Thunderbird versionOpen Thunderbird, go to Help > About Thunderbird (or run 'thunderbird --version' from command line) to see the exact version numberAffected if Version is below 128.10.1, or version is 129.0 through 138.0.0 (anything less than 138.0.1 but starting from 129.0)
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Confirm remote content blocking configurationGo to Thunderbird Settings > Privacy & Security and locate the 'Block remote content in messages' option (note: this setting is bypassed by the vulnerability but confirms the intended protection)Affected if Remote content blocking is enabled (the vulnerability bypasses this protection)
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 · scoped128.10.1138.0.1
Upgrade Thunderbird to version 128.10.1, 138.0.1, or later. No configuration workaround exists since the remote content blocking setting was insufficient.
Thunderbird 138.0.1 (or 128.10.1 for ESR users)
- Check the current Thunderbird version by opening Thunderbird and navigating to Help > About Thunderbird
- Download Thunderbird 138.0.1 (or 128.10.1 for the ESR branch) from the official Mozilla Thunderbird website at www.thunderbird.net
- Close Thunderbird completely before installing the update
- Run the installer for the downloaded Thunderbird version and follow the prompts to complete the upgrade
- After installation, verify the version by going to Help > About Thunderbird to confirm version 138.0.1 or 128.10.1 is installed
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation1.0 h
- Implementation1.0 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-2025-3932 — 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-2025-3932 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