FirefoxWeb browser · Mozilla
CVE-2024-3862
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 · uneditedThe MarkStack assignment operator, part of the JavaScript engine, could access uninitialized memory if it were used in a self-assignment. This vulnerability affects Firefox < 125.
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 confidenceThe MarkStack assignment operator in Firefox's JavaScript engine can access uninitialized memory when used in self-assignment scenarios. This memory safety issue in the JavaScript engine affects Firefox versions prior to 125.
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
< 125.0CVSS 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
- High
- Privileges
- None
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/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 checksWork through these to decide whether this CVE applies to you.
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Determine Firefox versionOpen Firefox, click the menu button (three horizontal lines), select Help, then About Firefox. The version number is displayed on this page.Affected if The displayed version is earlier than 125.0 (e.g., 124.0, 123.x, etc.)
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Verify JavaScript engine usageThe vulnerability exists in the JavaScript engine (SpiderMonkey). This engine is enabled by default in Firefox for all web pages and scripts.Affected if JavaScript is enabled in Firefox settings (default state)
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Check via command line (optional)On systems with Firefox installed from packages, run: firefox --version or about:firefox in the address barAffected if Command output shows a version number less than 125.0
You are affected if Firefox is installed with any version prior to 125.0 and JavaScript functionality is enabled (the default state).
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 · scoped125.0
Upgrade Firefox to version 125 or later to receive the patch for this JavaScript engine memory access vulnerability.
Firefox 125.0
- Verify current Firefox version by navigating to about:support or checking Help > About Firefox
- Back up any critical browser data (bookmarks, saved passwords) as a precautionary measure
- Download Firefox 125.0 or later from the official Mozilla website (www.mozilla.org) or use the browser's built-in update mechanism
- Install the updated Firefox version, which contains the fix for the MarkStack assignment operator vulnerability in the JavaScript engine
- Restart the browser after the update completes
- Verify the update was successful by checking the version in about:support - it should show 125.0 or higher
Generated from the published advisory — verify against the referenced sources before acting.
Fix this in Firefox
Scoped from the published advisory
- Consultation4.0 h
- Implementation8.0 h
- Testing8.0 h
- Review / QA4.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,656.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2024-3862 — 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-2024-3862 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
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- 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
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