What is CVE-2026-12323?

CVE-2026-12323 is a medium-severity vulnerability in Mozilla Firefox, classified under Improper Restriction of Rendered UI Layers or Frames (Clickjacking). CVSS score: 5.4/10. Published 2026-06-16.

How severe is CVE-2026-12323?

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

Vulnerability in Mozilla Firefox

CVE-2026-12323

Spoofing issue in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 152 and Thunderbird 152.

EPSS: 0.002 (6.5th 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:N/A:L.

Affected products

Mozilla Firefox — versions 152
Mozilla Thunderbird — versions 152

Weakness classification (CWE)

CWE-1021 — Improper Restriction of Rendered UI Layers or Frames (Clickjacking)

References

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

Frequently asked questions

What is CVE-2026-12323?: CVE-2026-12323 is a medium-severity vulnerability in Mozilla Firefox, classified under Improper Restriction of Rendered UI Layers or Frames (Clickjacking). CVSS score: 5.4/10. Published 2026-06-16.
How severe is CVE-2026-12323?: Medium severity. CVSS v3 base score is 5.4 out of 10.