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…

Vulnerability class: XSS (Cross-Site Scripting)

EPSS: 0.000 (11.5th percentile) — read the EPSS interpretation.

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.

Affected products

Mozilla Firefox
Mozilla Firefox For Ios — versions 151.2

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

security@mozilla.org (Permissions Required)
security@mozilla.org (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.