dbcve.org
ThunderbirdApplication · Mozilla

CVE-2025-26695

MEDIUM · 5.3 CVSS v3.1 Published 2025-03-10
Fix available
A fix is available. Upgrade to 128.8.0 / 136.0 or later.
See remediation →
55/100
Remediation priority · Elevated
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
When requesting an OpenPGP key from a WKD server, an incorrect padding size was used and a network observer could have learned the length of the requested email address. This vulnerability was fixed in Thunderbird 136 and Thunderbird 128.8.

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 used incorrect padding size when requesting OpenPGP keys from WKD (Web Key Directory) servers. This allowed network observers to passively determine the length of the email address being looked up, creating a privacy leak revealing which email addresses users were searching for public keys for.

MitigationUpdate Thunderbird to version 136 or later (or 128.8 ESR or later) to obtain the fixed padding implementation.

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:< 128.8.0>= 129.0, < 136.0

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
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
Low

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

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. Determine Thunderbird installation and version
    On the menu bar, click Help > About Thunderbird (or on macOS Thunderbird > About Thunderbird). The version number appears in the dialog that opens.
    Affected if The reported version is below 128.8.0, or is 129.x.x through 135.x.x (any version from 129.0 up to but not including 136.0).
  2. Verify OpenPGP is configured
    Go to Thunderbird Settings > Privacy & Security. Scroll to the End-to-End Encryption section and check if OpenPGP is enabled for any account.
    Affected if OpenPGP is enabled for one or more email accounts, because this enables WKD key lookups.
  3. Confirm WKD is in use for key lookups
    In Thunderbird Settings > Privacy & Security > End-to-End Encryption, check the key server settings for your accounts. WKD is used automatically when "Let Thunderbird find missing keys" or "Search on Web Key Directory" options are active.
    Affected if WKD-based key lookup is enabled (the default behavior when automatic key retrieval is permitted), meaning network observers can observe the unpadded request length.

A user is affected if Thunderbird version is 128.7.x or earlier, or any version from 129.0 through 135.x, AND OpenPGP with WKD key lookup is enabled.

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 128.8.0 / 136.0 or later
Fixed in 128.8.0136.0
Interim mitigation

Update Thunderbird to version 136 or later (or 128.8 ESR or later) to obtain the fixed padding implementation.

Recommended fix High confidence

Thunderbird 136.0 (or Thunderbird 128.8.0 for the extended support release branch)

  1. Check current Thunderbird version: On Windows, go to Help > About Thunderbird; on macOS, go to Thunderbird > About Thunderbird; or run 'thunderbird --version' from command line
  2. Download Thunderbird 136.0 or later from the official Mozilla website (www.mozilla.org)
  3. Alternatively, if you need to stay on the Extended Support Release, download Thunderbird 128.8.0 or later from the Mozilla website
  4. Close Thunderbird completely before installing the update
  5. Run the installer and follow the prompts to complete the upgrade
  6. After upgrading, verify the version by checking About Thunderbird to confirm you are on 136.0+ or 128.8.0+
Caveat Minor: Upgrading Thunderbird may introduce minor UI changes typical of version updates; no major breaking changes expected for this security patch

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

Fix this in Thunderbird Scoped from the published advisory
  • Consultation1.0 h
  • Testing1.0 h
  • Review / QA1.0 h
3.0 hours of engineering $750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,200.

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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-2025-26695 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