What is CVE-2026-8948?

CVE-2026-8948 is a critical-severity vulnerability in Mozilla Firefox, classified under Permissive Cross-domain Policy with Untrusted Domains. CVSS score: 9.1/10. Published 2026-05-19.

How severe is CVE-2026-8948?

Critical severity. CVSS v3 base score is 9.1 out of 10.

Vulnerability in Mozilla Firefox

CVE-2026-8948

Same-origin policy bypass in the DOM: Networking component. This vulnerability was fixed in Firefox 151 and Thunderbird 151.

EPSS: 0.000 (12.1th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.

Affected products

Mozilla Firefox — versions 151
Mozilla Thunderbird — versions 151

Weakness classification (CWE)

CWE-942 — Permissive Cross-domain Policy with Untrusted Domains

References

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

Frequently asked questions

What is CVE-2026-8948?: CVE-2026-8948 is a critical-severity vulnerability in Mozilla Firefox, classified under Permissive Cross-domain Policy with Untrusted Domains. CVSS score: 9.1/10. Published 2026-05-19.
How severe is CVE-2026-8948?: Critical severity. CVSS v3 base score is 9.1 out of 10.