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FirefoxWeb browser · Mozilla

CVE-2026-9309

MEDIUM · 5.4 CVSS v3.1 Published 2026-06-01
Fix available
A fix is available. Upgrade to 151.2 or later.
See remediation →
61/100
Remediation priority · Elevated
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
Firefox for iOS Reader View did not properly escape HTML tags in JSON-LD metadata. A malicious page could inject markup that changed Reader View behavior and leaked sensitive URL parameters. These parameters could then be used to access internal pages, potentially resulting in arbitrary JavaScript execution in an internal origin. This vulnerability was fixed in Firefox for iOS 151.2.

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

Cross-site scripting (XSS) vulnerability in Firefox for iOS Reader View where JSON-LD metadata is not properly escaped, allowing injection of malicious HTML tags. This enables leaking of sensitive URL parameters which can access internal pages and potentially achieve arbitrary JavaScript execution in internal origins.

MitigationUpdate Firefox for iOS to version 151.2 or later to remediate this 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:< 151.2

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
Low
Integrity
Low
Availability
None

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

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

  1. Check Firefox for iOS version
    Open the Firefox for iOS app, tap the menu (three lines), go to Settings, then tap About Firefox. The version number is displayed at the top.
    Affected if The version listed is less than 151.2 (for example, 151.1, 151.0, or any earlier version).
  2. Identify managed devices with Firefox for iOS
    Use your mobile device management (MDM) or enterprise mobility management (EMM) console to enumerate devices that have Firefox for iOS installed. Check the installed application inventory for Mozilla Firefox on iOS.
    Affected if Firefox for iOS is installed on any managed devices and the version cannot be verified as 151.2 or later.
  3. Verify Reader View accessibility
    In Firefox for iOS, navigate to any article-based webpage (such as a news article). Look for the Reader View icon in the address bar (usually a document icon).
    Affected if Reader View is accessible and functional on the device, indicating the affected feature is available.
  4. Audit internal applications using JSON-LD
    Review internal web applications and APIs that consume or display JSON-LD metadata. Check source code or network traffic for json-ld parsing, schema.org references, or structured data embedding.
    Affected if Internal applications process JSON-LD metadata from external or untrusted sources, which could be exploited if a user visits a malicious page in Reader View.

A user is affected if they have Firefox for iOS version less than 151.2 installed and use the Reader View feature, especially in environments with internal applications that handle JSON-LD metadata.

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 151.2 or later
Fixed in 151.2
Interim mitigation

Update Firefox for iOS to version 151.2 or later to remediate this vulnerability.

Recommended fix High confidence

Firefox for iOS 151.2

  1. Open the App Store on your iOS device
  2. Search for "Firefox" or locate Firefox for iOS in your purchased apps
  3. Tap Update to install Firefox for iOS version 151.2 or later
  4. Alternatively, enable automatic app updates in Settings > App Store to ensure you receive the security update

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Firefox Scoped from the published advisory
  • Consultation1.0 h
  • Testing2.0 h
  • Review / QA1.0 h
4.0 hours of engineering $750
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,200.

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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-2026-9309 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