What is CVE-2026-9308?

CVE-2026-9308 is a medium-severity vulnerability in Mozilla Firefox, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2026-06-01.

How severe is CVE-2026-9308?

Medium severity. CVSS v3 base score is 5.4 out of 10.

XSS in Mozilla Firefox

CVE-2026-9308

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.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2026-06-01 · last modified 2026-07-22.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.003 (16.4th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 16th percentile — 16.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001

Affected products

Mozilla Firefox
Mozilla Firefox For iOS — versions 151.2

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-53/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-9308?: CVE-2026-9308 is a medium-severity vulnerability in Mozilla Firefox, classified under Cross-site Scripting. CVSS score: 5.4/10. Published 2026-06-01.
How severe is CVE-2026-9308?: Medium severity. CVSS v3 base score is 5.4 out of 10.