What is CVE-2026-8971?

CVE-2026-8971 is a medium-severity vulnerability in Mozilla Firefox, classified under Origin Validation Error. CVSS score: 6.5/10. Published 2026-05-19.

How severe is CVE-2026-8971?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Mozilla Firefox

CVE-2026-8971

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

EPSS: 0.000 (5.3th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.

Affected products

Mozilla Firefox — versions 151
Mozilla Thunderbird — versions 151

Weakness classification (CWE)

CWE-346 — Origin Validation Error

References

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

Frequently asked questions

What is CVE-2026-8971?: CVE-2026-8971 is a medium-severity vulnerability in Mozilla Firefox, classified under Origin Validation Error. CVSS score: 6.5/10. Published 2026-05-19.
How severe is CVE-2026-8971?: Medium severity. CVSS v3 base score is 6.5 out of 10.