What is CVE-2026-12327?

CVE-2026-12327 is a high-severity vulnerability in Mozilla Firefox, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 7.3/10. Published 2026-06-16.

How severe is CVE-2026-12327?

High severity. CVSS v3 base score is 7.3 out of 10.

Buffer overflow in Mozilla Firefox

CVE-2026-12327

Memory safety bugs present in Firefox ESR 140.11, Thunderbird ESR 140.11, Firefox 151 and Thunderbird 151. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploit…

Vulnerability class: Buffer Overflow

CVSS v3 metric

CVSS v3 base score 7.3 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L.

Affected products

Mozilla Firefox — versions 140.12, 152
Mozilla Thunderbird — versions 140.12, 152

Weakness classification (CWE)

CWE-119 — Improper Restriction of Operations within the Bounds of a Memory Buffer

References

Frequently asked questions

What is CVE-2026-12327?: CVE-2026-12327 is a high-severity vulnerability in Mozilla Firefox, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 7.3/10. Published 2026-06-16.
How severe is CVE-2026-12327?: High severity. CVSS v3 base score is 7.3 out of 10.