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FirefoxWeb browser · Mozilla

CVE-2020-15681

HIGH · 7.5 CVSS v3.1 Published 2020-10-22
Fix available
A fix is available. Upgrade to 82.0 or later.
See remediation →
84/100
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
When multiple WASM threads had a reference to a module, and were looking up exported functions, one WASM thread could have overwritten another's entry in a shared stub table, resulting in a potentially exploitable crash. This vulnerability affects Firefox < 82.

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 race condition in Firefox's WebAssembly implementation allows one WASM thread to overwrite another's entry in a shared stub table during exported function lookups, potentially causing an exploitable crash.

MitigationUpgrade to Firefox 82 or later. If using custom WASM modules with threading, ensure proper synchronization around stub table access.

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:< 82.0

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
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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. Determine installed Firefox version
    Run 'firefox --version' from command line, or open 'about:support' in the browser address bar and locate the 'Version' field under 'Application Basics'
    Affected if Version number is less than 82.0 (e.g., 81.x, 80.x, etc.)
  2. Verify WebAssembly threading is enabled
    Open 'about:config' in the browser address bar, then search for the preference 'javascript.options.wasm_threads'
    Affected if The preference 'javascript.options.wasm_threads' is set to true (enabled)
  3. Confirm SharedArrayBuffer usage in loaded WASM modules
    Open the browser's Developer Tools (F12), go to the Network tab, filter for '.wasm' files, and inspect response headers for 'Cross-Origin-Opener-Policy' and 'Cross-Origin-Embedder-Policy' headers which enable SharedArrayBuffer
    Affected if WASM modules using SharedArrayBuffer are loaded and the browser version is below 82.0

User is affected if running Firefox version below 82.0 AND WebAssembly threading is enabled or WASM modules using SharedArrayBuffer are in use.

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.

From vendor data
Upgrade available Upgrade to 82.0 or later
Fixed in 82.0
Interim mitigation

Upgrade to Firefox 82 or later. If using custom WASM modules with threading, ensure proper synchronization around stub table access.

Fix this in Firefox Scoped from the published advisory
  • Consultation3.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
17.0 hours of engineering $3,000
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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-2020-15681 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