What is CVE-2026-8963?

CVE-2026-8963 is a high-severity vulnerability in Mozilla Firefox, classified under Authentication Bypass by Spoofing. CVSS score: 7.5/10. Published 2026-05-19.

How severe is CVE-2026-8963?

High severity. CVSS v3 base score is 7.5 out of 10.

Vulnerability in Mozilla Firefox

CVE-2026-8963

Spoofing issue in the Web Speech component. This vulnerability was fixed in Firefox 151 and Thunderbird 151.

Published 2026-05-19 · last modified 2026-07-23.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.004 (32.0th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 32nd percentile — 32.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.004 · change: +0.001

Affected products

Mozilla Firefox — versions 151
Mozilla Thunderbird — versions 151

Weakness classification (CWE)

CWE-290 — Authentication Bypass by Spoofing

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-46/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-50/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-8963?: CVE-2026-8963 is a high-severity vulnerability in Mozilla Firefox, classified under Authentication Bypass by Spoofing. CVSS score: 7.5/10. Published 2026-05-19.
How severe is CVE-2026-8963?: High severity. CVSS v3 base score is 7.5 out of 10.