What is CVE-2026-12303?

CVE-2026-12303 is a medium-severity vulnerability in Mozilla Firefox, classified under Out-of-bounds Read. CVSS score: 4.3/10. Published 2026-06-16.

How severe is CVE-2026-12303?

Medium severity. CVSS v3 base score is 4.3 out of 10.

Out-of-bounds Read in Mozilla Firefox

CVE-2026-12303

Information disclosure due to incorrect boundary conditions in the Graphics: WebGPU component. This vulnerability was fixed in Firefox 152 and Thunderbird 152.

Vulnerability class: Buffer Overflow

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

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.002 (11.5th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 11th percentile — 11.5% 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 152
Mozilla Thunderbird — versions 152

Weakness classification (CWE)

CWE-125 — Out-of-bounds Read

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-57/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-60/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-12303?: CVE-2026-12303 is a medium-severity vulnerability in Mozilla Firefox, classified under Out-of-bounds Read. CVSS score: 4.3/10. Published 2026-06-16.
How severe is CVE-2026-12303?: Medium severity. CVSS v3 base score is 4.3 out of 10.