What is CVE-2026-2804?

CVE-2026-2804 is a medium-severity vulnerability in Mozilla Firefox, classified under Use After Free. CVSS score: 5.4/10. Published 2026-02-24.

How severe is CVE-2026-2804?

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

Use After Free in Mozilla Firefox

CVE-2026-2804

Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 148 and Thunderbird 148.

Vulnerability class: Use-After-Free

Published 2026-02-24 · 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: 0.003 (19.2th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 19th percentile — 19.2% 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: 0.003 · change: 0.000

Affected products

Mozilla Firefox — versions 148
Mozilla Thunderbird — versions 148

Weakness classification (CWE)

CWE-416 — Use After Free

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-13/ (Vendor Advisory)
www.mozilla.org/security/advisories/mfsa2026-16/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-2804?: CVE-2026-2804 is a medium-severity vulnerability in Mozilla Firefox, classified under Use After Free. CVSS score: 5.4/10. Published 2026-02-24.
How severe is CVE-2026-2804?: Medium severity. CVSS v3 base score is 5.4 out of 10.