What is CVE-2026-6758?

CVE-2026-6758 is a high-severity vulnerability in Mozilla Firefox, classified under Use After Free. CVSS score: 7.5/10. Published 2026-04-21.

How severe is CVE-2026-6758?

High severity. CVSS v3 base score is 7.5 out of 10.

Use After Free in Mozilla Firefox

CVE-2026-6758

Use-after-free in the JavaScript: WebAssembly component. This vulnerability was fixed in Firefox 150 and Thunderbird 150.

Vulnerability class: Use-After-Free

Published 2026-04-21 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.005 (40.6th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 41st percentile — 40.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: -0.000

Affected products

Mozilla Firefox — versions 150
Mozilla Thunderbird — versions 150

Weakness classification (CWE)

CWE-416 — Use After Free

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)

Frequently asked questions

What is CVE-2026-6758?: CVE-2026-6758 is a high-severity vulnerability in Mozilla Firefox, classified under Use After Free. CVSS score: 7.5/10. Published 2026-04-21.
How severe is CVE-2026-6758?: High severity. CVSS v3 base score is 7.5 out of 10.