What is CVE-2026-12330?

CVE-2026-12330 is a medium-severity vulnerability in Mozilla Firefox, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 5.4/10. Published 2026-06-16.

How severe is CVE-2026-12330?

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

Buffer overflow in Mozilla Firefox

CVE-2026-12330

Incorrect boundary conditions in the Internationalization component. This vulnerability was fixed in Firefox ESR 140.12, Firefox ESR 115.37, and Thunderbird 140.12.

Vulnerability class: Buffer Overflow

Published 2026-06-16 · last modified 2026-06-17.

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.

EPSS exploit prediction

EPSS: 0.002 (5.0th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 5th percentile — 5.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: 0.000

Affected products

Mozilla Firefox — versions 115.37, 140.12
Mozilla Thunderbird — versions 140.12

Weakness classification (CWE)

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

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-58/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-59/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-61/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-12330?: CVE-2026-12330 is a medium-severity vulnerability in Mozilla Firefox, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 5.4/10. Published 2026-06-16.
How severe is CVE-2026-12330?: Medium severity. CVSS v3 base score is 5.4 out of 10.