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FirefoxWeb browser · Mozilla

CVE-2024-7521

HIGH · 8.8 CVSS v3.1 Published 2024-08-06
Fix available
A fix is available. Upgrade to 115.14.0 / 129.0 or later.
See remediation →
95/100
Remediation priority · Urgent
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
Incomplete WebAssembly exception handing could have led to a use-after-free. This vulnerability affects Firefox < 129, Firefox ESR < 115.14, Firefox ESR < 128.1, Thunderbird < 128.1, and Thunderbird < 115.14.

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

Incomplete WebAssembly exception handling in Firefox and Thunderbird contains a flaw that could lead to a use-after-free vulnerability, potentially allowing memory corruption and possibly remote code execution through malicious Wasm code.

MitigationUpgrade to Firefox 129, Firefox ESR 115.14/128.1, or Thunderbird 128.1/115.14 or later to remediate this use-after-free vulnerability in WebAssembly exception handling.

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:< 129.0
Firefox EsrWeb browser
Affected:< 115.14.0= 128.0
ThunderbirdApplication
Affected:< 115.14.0= 128.0.1

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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Firefox version
    Open Firefox, go to Menu > Help > About Firefox, or navigate to about:support, to see the exact version number
    Affected if Version is less than 129.0, or version is 128.0 (any build), or ESR versions are less than 115.14.0 or equal to 128.1.0 (for ESR)
  2. Identify installed Thunderbird version
    Open Thunderbird, go to Menu > Help > About Thunderbird to display the version number
    Affected if Version is less than 115.14.0, or version equals 128.0.1
  3. Verify WebAssembly support status
    In the browser address bar, enter about:config and search for javascript.options.wasm. Confirm the preference exists and is enabled (typically true by default)
    Affected if WebAssembly is enabled in the browser settings, which is the default state - the vulnerability triggers when processing malicious Wasm code with exception handling
  4. Check Firefox ESR branch in use
    In about:support, look at the Version field. ESR versions display 'ESR' in the version string (for example, '115.14.0 ESR' or '128.1.0 ESR')
    Affected if Running Firefox ESR 115.x versions below 115.14.0, or ESR 128.x versions equal to 128.0.0 (128.0 is affected, 128.1 is fixed)

You are affected if you run Firefox below 129.0, Firefox ESR 115.14.0 or below (excluding 115.14.0), Firefox ESR 128.0, or Thunderbird below 115.14.0 or version 128.0.1, with WebAssembly enabled (the default).

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 115.14.0 / 129.0 or later
Fixed in 115.14.0129.0
Interim mitigation

Upgrade to Firefox 129, Firefox ESR 115.14/128.1, or Thunderbird 128.1/115.14 or later to remediate this use-after-free vulnerability in WebAssembly exception handling.

Recommended fix High confidence

Firefox 129.0; Firefox ESR 115.14.0 or 128.1.0; Thunderbird 115.14.0 or 128.1.0

  1. Check current Firefox or Thunderbird version (Help > About Firefox/Thunderbird)
  2. Download Firefox 129.0 from mozilla.org or Firefox ESR 115.14.0/128.1.0 from mozilla.org
  3. Download Thunderbird 115.14.0 or 128.1.0 from mozilla.org if affected
  4. Install the downloaded version
  5. Restart the application
Caveat Standard security update with no expected breaking changes

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
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,120.

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-2024-7521 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