FirefoxWeb browser · Mozilla
CVE-2021-29953
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 · uneditedA malicious webpage could have forced a Firefox for Android user into executing attacker-controlled JavaScript in the context of another domain, resulting in a Universal Cross-Site Scripting vulnerability. *Note: This issue only affected Firefox for Android. Other operating systems are unaffected. Further details are being temporarily withheld to allow users an opportunity to update.*. This vulnerability affects Firefox < 88.0.1 and Firefox for Android < 88.1.3.
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 · moderate confidenceA Universal Cross-Site Scripting (UXSS) vulnerability in Firefox for Android allows a malicious webpage to force execution of attacker-controlled JavaScript in the context of a different domain. This cross-origin JavaScript execution occurs due to improper handling of browser context or origin isolation in the Firefox for Android browser engine.
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
< 88.0.1< 88.1.3CVSS 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
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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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Confirm Firefox for Android is installedOpen the device settings, go to Apps, and look for Mozilla Firefox in the installed applications list, or check the app icon on the home screenAffected if Firefox for Android is not present on the device
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Find the installed Firefox for Android version numberOpen Firefox for Android, tap the three-dot menu, go to Settings, then scroll down and tap 'About Firefox' - the version number will be displayedAffected if Cannot locate version information or the app is not Firefox for Android
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Compare installed version against affected rangeNote the version number from the About screen and compare it to the affected versions: any version below 88.1.3 is considered vulnerableAffected if Installed version is less than 88.1.3 (for example, 88.0, 87.x, or earlier)
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Verify the update statusIn Firefox for Android, tap the three-dot menu and look for an 'Update' option in Settings, or visit the Google Play Store and check for Firefox updatesAffected if A newer version is available or the browser has not been updated to 88.1.3 or later
The user is affected if Firefox for Android is installed with a version number lower than 88.1.3, as this UXSS vulnerability allows cross-origin JavaScript execution through improper browser context handling.
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.
From vendor data88.0.188.1.3
Update Firefox for Android to version 88.1.3 or later to patch this UXSS vulnerability. Organizations should ensure mobile devices are running the patched browser version.
Fix this in Firefox
Scoped from the published advisory
- Consultation3.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,304.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-29953 — 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-2021-29953 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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