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FirefoxWeb browser · Mozilla

CVE-2025-1933

HIGH · 7.6 CVSS v3.1 Published 2025-03-04
Fix available
A fix is available. Upgrade to 115.21.0 / 128.8 or later.
See remediation →
83/100
Remediation priority · High
Remotely reachable No privileges

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
On 64-bit CPUs, when the JIT compiles WASM i32 return values they can pick up bits from left over memory. This can potentially cause them to be treated as a different type. This vulnerability was fixed in Firefox 136, Firefox ESR 115.21, 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

A JIT compiler bug in Firefox and Thunderbird on 64-bit CPUs causes WebAssembly i32 return values to potentially pick up leftover bits from memory, which could be misinterpreted as a different type leading to type confusion.

MitigationUpgrade to Firefox 136+, Firefox ESR 115.21+, Firefox ESR 128.8+, Thunderbird 136+, or Thunderbird 128.8+ to apply the vendor patch.

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:< 115.21.0< 136.0>= 116.0, < 128.8.0
ThunderbirdApplication
Affected:< 128.8>= 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
Required
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
High

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

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. Identify installed Mozilla product
    Check if Firefox or Thunderbird is installed. In Firefox, enter 'about:support' in the address bar and look at the 'Application' section. In Thunderbird, go to 'Help' > 'About Thunderbird'.
    Affected if Product is Firefox or Thunderbird (the bug only affects these products)
  2. Determine exact version number
    Note the full version number shown in the application's About page (e.g., 128.7.0, 115.20.0, 135.0.1).
    Affected if Version cannot be determined or is not visible
  3. Compare Firefox version to affected ranges
    For Firefox: Compare your version against the affected ranges: < 115.21.0, >= 116.0 and < 128.8.0, or < 136.0. If your version falls into any of these ranges, you are affected.
    Affected if Firefox version is less than 115.21.0, OR between 116.0 and 127.x, OR between 128.0 and 128.7.x, OR less than 136.0 (non-ESR releases)
  4. Compare Thunderbird version to affected ranges
    For Thunderbird: Compare your version against < 128.8 or >= 129.0 and < 136.0. If your version falls into either range, you are affected.
    Affected if Thunderbird version is less than 128.8, OR between 129.0 and 135.x
  5. Confirm WebAssembly usage (context)
    Review whether any loaded web content or extensions are actively using WebAssembly modules, as the vulnerability specifically affects JIT-compiled WebAssembly i32 return values. Check browser console for WebAssembly errors or inspect network activity for .wasm file loads.
    Affected if WebAssembly is actively being used and the browser version is in the affected range

You are affected if you have Firefox < 115.21.0, Firefox >= 116.0 and < 128.8.0, Firefox < 136.0 (non-ESR), Thunderbird < 128.8, or Thunderbird >= 129.0 and < 136.0, and are actively using WebAssembly content.

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 115.21.0 / 128.8 / 128.8.0 or later
Fixed in 115.21.0128.8128.8.0
Interim mitigation

Upgrade to Firefox 136+, Firefox ESR 115.21+, Firefox ESR 128.8+, Thunderbird 136+, or Thunderbird 128.8+ to apply the vendor patch.

Recommended fix High confidence

Firefox 136.0 (or Firefox ESR 115.21/128.8); Thunderbird 136.0 (or 128.8)

  1. Open Firefox or Thunderbird and go to Help > About to check the current version
  2. For Firefox: Navigate to https://www.mozilla.org/en-US/firefox/ and download version 136.0 or later (or ESR 128.8/115.21 for ESR users)
  3. For Thunderbird: Navigate to https://www.mozilla.org/en-US/thunderbird/ and download version 128.8 or later (or 136.0)
  4. Run the downloaded installer to update the application
  5. Restart the browser or email client after the update completes
  6. Verify the version by checking Help > About - it should show 136.0+ (or 128.8+ for Thunderbird, or 115.21+ for Firefox ESR)
Caveat Standard security update with no expected breaking changes; always backup important data before updating

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

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
7.0 hours of engineering $1,240
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,984.

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-2025-1933 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