What is CVE-2026-12321?

CVE-2026-12321 is a medium-severity vulnerability in Mozilla Firefox, classified under Always-Incorrect Control Flow Implementation. CVSS score: 5.4/10. Published 2026-06-16.

How severe is CVE-2026-12321?

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

Vulnerability in Mozilla Firefox

CVE-2026-12321

JIT miscompilation in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 152 and Thunderbird 152.

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 — versions 152
Mozilla Thunderbird — versions 152

Weakness classification (CWE)

CWE-670 — Always-Incorrect Control Flow Implementation

References

security@mozilla.org
security@mozilla.org
security@mozilla.org

Frequently asked questions

What is CVE-2026-12321?: CVE-2026-12321 is a medium-severity vulnerability in Mozilla Firefox, classified under Always-Incorrect Control Flow Implementation. CVSS score: 5.4/10. Published 2026-06-16.
How severe is CVE-2026-12321?: Medium severity. CVSS v3 base score is 5.4 out of 10.