What’s Vulnerable › Vulnerabilities

CVE-2026-9309: Arbitrary JavaScript execution in internal pages via Reader View JSON-LD injection

• Severity: medium (CVSS 5.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-06-01 · updated 2026-07-22
• Weakness: CWE-79

Description

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.

Affected products

• Mozilla Firefox: before 151.2 — fixed in 151.2

How to fix

Upgrade to a fixed version: Mozilla Firefox 151.2. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/show_bug.cgi?id=2036573
• https://www.mozilla.org/security/advisories/mfsa2026-53/

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