What is CVE-2026-7321?

CVE-2026-7321 is a critical-severity vulnerability in Mozilla Firefox, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.6/10. Published 2026-04-28.

How severe is CVE-2026-7321?

Critical severity. CVSS v3 base score is 9.6 out of 10.

Buffer overflow in Mozilla Firefox

CVE-2026-7321

Sandbox escape due to incorrect boundary conditions in the WebRTC: Networking component. This vulnerability was fixed in Firefox 150, Thunderbird 150, Firefox ESR 140.10.1, and Thunderbird 140.10.1.

Vulnerability class: Buffer Overflow

Published 2026-04-28 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.6 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (36.6th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 37th percentile — 36.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.003 · newest: 0.004 · change: +0.002

Affected products

Mozilla Firefox — versions 140.10.1, 150
Mozilla Thunderbird — versions 140.10.1, 150

Weakness classification (CWE)

CWE-120 — Buffer Copy without Checking Size of Input (Classic Buffer Overflow)

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-30/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-33/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-36/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-39/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-7321?: CVE-2026-7321 is a critical-severity vulnerability in Mozilla Firefox, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 9.6/10. Published 2026-04-28.
How severe is CVE-2026-7321?: Critical severity. CVSS v3 base score is 9.6 out of 10.