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FirefoxWeb browser · Mozilla

CVE-2025-1936

HIGH · 7.3 CVSS v3.1 Published 2025-03-04
Fix available
A fix is available. Upgrade to 128.8.0 / 136.0 or later.
See remediation →
82/100
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
jar: URLs retrieve local file content packaged in a ZIP archive. The null and everything after it was ignored when retrieving the content from the archive, but the fake extension after the null was used to determine the type of content. This could have been used to hide code in a web extension disguised as something else like an image. This vulnerability was fixed in Firefox 136, Firefox ESR 128.8, 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

The jar: URL handler in Firefox and Thunderbird improperly processes null bytes in ZIP archive file paths. When retrieving content from a JAR/ZIP archive, everything after the null byte is ignored for content retrieval, but the fake extension after the null is used to determine the MIME content type. This allows malicious code packaged in a web extension to be disguised as harmless file types like images, potentially bypassing security checks.

MitigationUpdate vulnerable installations to Firefox 136, Firefox ESR 128.8, Thunderbird 136, or Thunderbird 128.8 respectively, or later versions.

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
FirefoxWeb browser
Affected:< 128.8.0< 136.0
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
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/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. Check Firefox version
    Open Firefox, go to Menu > Help > About Firefox (or navigate to about:support). Note the version number displayed.
    Affected if Version is less than 128.8.0 OR between 129.0 and 135.x (inclusive)
  2. Check Thunderbird version
    Open Thunderbird, go to Menu > Help > About Thunderbird. Note the version number displayed.
    Affected if Version is less than 128.8.0 OR between 129.0 and 135.x (inclusive)
  3. Verify jar URL handling is active
    The jar: URL handler is built into Firefox and Thunderbird and processes any jar: or xpi: URLs encountered. No configuration needed - it is always active when the application processes extension files or JAR archives.
    Affected if Application uses the built-in jar handler to process ZIP-based archives (common for extensions, add-ons, and Java Web Start applications)

You are affected if Firefox is below 128.8.0 or is version 129.0 through 135.x, or if Thunderbird is below 128.8.0 or is version 129.0 through 135.x, since these versions contain the vulnerable jar: URL handler that improperly processes null bytes in ZIP file paths.

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 vulnerable installations to Firefox 136, Firefox ESR 128.8, Thunderbird 136, or Thunderbird 128.8 respectively, or later versions.

Recommended fix High confidence

Firefox 136.0+ (or Firefox ESR 128.8+); Thunderbird 136.0+ (or Thunderbird 128.8+)

  1. Upgrade Firefox to version 136.0 or later for the main release track
  2. If using Firefox ESR, upgrade to version 128.8 or later
  3. Upgrade Thunderbird to version 136.0 or later for the main release track
  4. If using Thunderbird 128.x ESR-style releases, upgrade to version 128.8 or later
  5. Verify the upgrade was successful by checking Help > About Firefox or Help > About Thunderbird

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

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Implementation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
5.0 hours of engineering $860
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,376.

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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-2025-1936 in production — separate from our analysis above.

No notes yet

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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