FirefoxWeb browser · Mozilla
CVE-2025-1942
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 · uneditedWhen String.toUpperCase() caused a string to get longer it was possible for uninitialized memory to be incorporated into the result string. This vulnerability was fixed in Firefox 136 and Thunderbird 136.
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 confidenceWhen String.toUpperCase() causes a string to expand in length, uninitialized memory can be incorporated into the result string, leading to potential information disclosure. This memory safety flaw affects Firefox 136 and Thunderbird 136.
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
< 136.0< 136.0CVSS 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
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 checksWork through these to decide whether this CVE applies to you.
-
Check if Firefox is installedOn Windows, check C:\Program Files\Mozilla Firefox\application.ini for Version line, or run 'firefox --version' in command line. On macOS, run '/Applications/Firefox.app/Contents/MacOS/firefox --version' or check via About Firefox menu. On Linux, run 'firefox --version' or check package manager.Affected if Firefox is installed with version lower than 136.0
-
Check if Thunderbird is installedOn Windows, check C:\Program Files\Mozilla Thunderbird\application.ini for Version line, or run 'thunderbird --version' in command line. On macOS, run '/Applications/Thunderbird.app/Contents/MacOS/thunderbird --version' or check via About Thunderbird menu. On Linux, run 'thunderbird --version' or check package manager.Affected if Thunderbird is installed with version lower than 136.0
You are affected if either Mozilla Firefox or Thunderbird is installed with a version below 136.0, as the vulnerability exists in the String.toUpperCase() string expansion handling of these versions.
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 · scoped136.0
Update to Firefox 136 or Thunderbird 136 or later to obtain the patched version that properly initializes memory during string case conversion.
Firefox 136.0+ / Thunderbird 136.0+
- Check current Firefox version by navigating to about:Firefox in the address bar
- Check current Thunderbird version by going to Help > About Thunderbird
- If Firefox is below version 136.0, update to Firefox 136.0 or later via Help > About Firefox > Check for Updates
- If Thunderbird is below version 136.0, update to Thunderbird 136.0 or later via Help > About Thunderbird > Check for Updates
- Restart the application after 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
- Implementation1.0 h
- Testing1.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,456.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-1942 — 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-2025-1942 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
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
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.
- 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