What is CVE-2025-11721?

CVE-2025-11721 is a critical-severity vulnerability in Mozilla Firefox, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 9.8/10. Published 2025-10-14.

How severe is CVE-2025-11721?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Buffer overflow in Mozilla Firefox

CVE-2025-11721

Memory safety bug present in Firefox 143 and Thunderbird 143. This bug showed evidence of memory corruption and we presume that with enough effort this could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 144 and Thunderbird 144.

Vulnerability class: Buffer Overflow

Published 2025-10-14 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (27.8th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 28th percentile — 27.8% 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: +0.000

Affected products

Mozilla Firefox — versions 144
Mozilla Thunderbird — versions 144

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, Issue Tracking)
www.mozilla.org/security/advisories/mfsa2025-81/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2025-84/ (Vendor Advisory)

Frequently asked questions

What is CVE-2025-11721?: CVE-2025-11721 is a critical-severity vulnerability in Mozilla Firefox, classified under Improper Restriction of Operations within the Bounds of a Memory Buffer. CVSS score: 9.8/10. Published 2025-10-14.
How severe is CVE-2025-11721?: Critical severity. CVSS v3 base score is 9.8 out of 10.