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FirefoxWeb browser · Mozilla

CVE-2021-23957

HIGH · 7.4 CVSS v3.1 Published 2021-02-26
Fix available
A fix is available. Upgrade to 85.0 or later.
See remediation →
81/100
Remediation priority · High
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
Navigations through the Android-specific `intent` URL scheme could have been misused to escape iframe sandbox. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85.

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

Firefox for Android versions prior to 85 contains a sandbox bypass vulnerability where the Android-specific 'intent' URL scheme can be misused during navigation to escape iframe sandbox restrictions, allowing potentially malicious web content to perform actions outside the intended sandbox boundaries.

MitigationUpgrade Firefox for Android to version 85 or later on all affected devices to remediate this sandbox escape vulnerability.

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:< 85.0

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
Required
Scope
Changed
Confidentiality
None
Integrity
High
Availability
None

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

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

  1. Verify Firefox for Android is installed
    On the Android device, go to Settings > Apps and look for Firefox, or use ADB: adb shell pm list packages | grep -i firefox
    Affected if Firefox for Android package (org.mozilla.firefox) is found on the device
  2. Retrieve Firefox for Android version number
    On the device, go to Settings > Apps > Firefox > Version information, or use ADB command: adb shell dumpsys package org.mozilla.firefox | grep versionName
    Affected if Version number cannot be retrieved or Firefox for Android is not installed
  3. Compare version against affected range
    Check if the installed version is less than 85.0 (e.g., 84.2.0, 84.1.2, 83.0, etc.)
    Affected if Installed version is 84.x or any version lower than 85.0

The environment is affected if Firefox for Android with version below 85.0 is installed and the browser handles web content with iframes using the intent URL scheme.

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 85.0 or later
Fixed in 85.0
Interim mitigation

Upgrade Firefox for Android to version 85 or later on all affected devices to remediate this sandbox escape vulnerability.

Fix this in Firefox Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,420
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,272.

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-2021-23957 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