CVE-2026-9308: Arbitrary JavaScript execution in Reader View due to wrong HTML replacement order

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 replaced page content in its HTML template before replacing other internal placeholders. A malicious page could include a placeholder string that was later substituted with JSON-LD data, potentially resulting in arbitrary JavaScript execution. 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=2039422
https://www.mozilla.org/security/advisories/mfsa2026-53/

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