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ThunderbirdApplication · Mozilla

CVE-2025-3875

HIGH · 7.5 CVSS v3.1 Published 2025-05-14
Fix available
A fix is available. Upgrade to 128.10.0 / 138.0.1 or later.
See remediation →
84/100
Remediation priority · High
Remotely reachable No privileges Zero-click

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 · unedited
Thunderbird parses addresses in a way that can allow sender spoofing in case the server allows an invalid From address to be used. For example, if the From header contains an (invalid) value "Spoofed Name ", Thunderbird treats [email protected] as the actual address. 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 confidence

Thunderbird incorrectly parses email addresses from the From header, treating content after invalid portions as the actual sender address. When a From header contains malformed addresses (e.g., 'Spoofed Name '), Thunderbird extracts what appears to be a valid address ([email protected]) even when it's invalid, enabling sender spoofing attacks.

MitigationUpdate Thunderbird to version 128.10.1 or 138.0.1 or later. Consider implementing additional email authentication (SPF, DKIM, DMARC) on mail servers as a defense-in-depth measure.

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
ThunderbirdApplication
Affected:< 128.10.0>= 129.0, < 138.0.1

CVSS 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
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/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 checks

Work through these to decide whether this CVE applies to you.

  1. Locate Thunderbird installation
    Open Thunderbird and navigate to Help > About Thunderbird (on Windows/Linux) or Thunderbird > About Thunderbird (on macOS). Alternatively, run 'thunderbird --version' from a command line.
    Affected if Thunderbird is installed on the system
  2. Identify installed Thunderbird version
    Note the version number displayed in the About window or command output (e.g., 128.9.0, 129.0, 137.0.2, 138.0.1).
    Affected if Version cannot be determined or is in the vulnerable range
  3. Compare against vulnerable version ranges
    Check if the installed version is less than 128.10.0, OR greater than or equal to 129.0 but less than 138.0.1. Versions 128.10.0 through 128.10.x and 138.0.1 and later are not affected.
    Affected if Version falls in < 128.10.0 OR (>= 129.0 AND < 138.0.1)
  4. Verify From header parsing behavior (optional)
    Receive or open an email with a malformed From header containing invalid portions (e.g., 'Name ' with trailing spaces or other malformed content). Observe whether Thunderbird extracts and displays what appears to be a valid email address from the invalid portion.
    Affected if Thunderbird displays a valid-looking email address extracted from invalid header content (potential spoofing vulnerability present)

If Thunderbird version is less than 128.10.0 or between 129.0 and 138.0.1 inclusive, the environment is affected by this sender spoofing vulnerability.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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 · scoped
Upgrade available Upgrade to 128.10.0 / 138.0.1 or later
Fixed in 128.10.0138.0.1
Interim mitigation

Update Thunderbird to version 128.10.1 or 138.0.1 or later. Consider implementing additional email authentication (SPF, DKIM, DMARC) on mail servers as a defense-in-depth measure.

Recommended fix High confidence

Thunderbird 128.10.1 or Thunderbird 138.0.1 (depending on current branch)

  1. Check current Thunderbird version: Help > About Thunderbird
  2. If version is < 128.10.0 (e.g., 128.9.x): upgrade to Thunderbird 128.10.1
  3. If version is >= 129.0 and < 138.0.1 (e.g., 129.x, 138.0.0): upgrade to Thunderbird 138.0.1
  4. Download the appropriate fixed version from www.mozilla.org/thunderbird or use the built-in update mechanism (Check for Updates)

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Thunderbird Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
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Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-3875 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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