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FirefoxWeb browser · Mozilla

CVE-2021-29971

CRITICAL · 9.8 CVSS v3.1 Published 2021-08-05
Fix available
A fix is available. Upgrade to 90.0 or later.
See remediation →
100/100
Remediation priority · Urgent
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
If a user had granted a permission to a webpage and saved that grant, any webpage running on the same host - irrespective of scheme or port - would be granted that permission. *This bug only affects Firefox for Android. Other operating systems are unaffected.*. This vulnerability affects Firefox < 90.

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 permission bypass vulnerability in Firefox for Android allows any webpage on the same host to inherit permission grants originally given to a different webpage, regardless of scheme or port differences. This occurs because saved permission state is incorrectly shared across all URLs sharing a host, rather than being scoped to the exact origin (scheme+host+port tuple).

MitigationUpgrade Firefox for Android to version 90 or later. Organizations should inventory and update all Android devices running older Firefox versions, as desktop Firefox installations are unaffected by this flaw.

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:< 90.0

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
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 checks

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

  1. Identify Firefox for Android installation
    On the Android device, go to Settings > Apps and locate Firefox. Confirm it is the standard Firefox for Android app (not Firefox Lite or Firefox Focus).
    Affected if The standard Firefox for Android browser is installed on the device.
  2. Check Firefox for Android version
    In Settings > Apps > Firefox, view the version information. Compare the version number to the affected range (versions prior to 90.0).
    Affected if The installed version is below 90.0.
  3. Review granted website permissions
    Open Firefox for Android, tap the three-dot menu, go to Settings > Permissions. Examine all permissions listed (such as Location, Camera, Microphone, Notifications). Check which origins have been granted these permissions.
    Affected if Any permission has been granted to one or more websites, as these grants could be inherited by other same-host origins due to the flaw.
  4. Check for cross-origin permission grants on same host
    Review the granted permissions list and identify if multiple websites with different schemes (http/https) or ports but the same host have different permission states. The flaw causes permissions to be shared incorrectly across all URLs sharing a host.
    Affected if Multiple origins on the same host exist with varying permission states, indicating potential unintended permission inheritance.

A user is affected if Firefox for Android version is below 90.0 and the browser has granted any permissions to websites, because same-host origins can incorrectly inherit those permission grants.

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 90.0 or later
Fixed in 90.0
Interim mitigation

Upgrade Firefox for Android to version 90 or later. Organizations should inventory and update all Android devices running older Firefox versions, as desktop Firefox installations are unaffected by this flaw.

Recommended fix High confidence

Firefox 90.0 (or later) for Android

  1. 1. Open Firefox for Android on the device
  2. 2. Navigate to Settings > Help > About Firefox
  3. 3. If the version shown is below 90.0, select 'Update' to download and install Firefox 90.0 or later
  4. 4. Restart the browser after the update completes
Caveat Minimal - this is a security update for Firefox for Android only; other Firefox versions/platforms are unaffected

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-2021-29971 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