What is CVE-2026-3846?

CVE-2026-3846 is a medium-severity vulnerability in Mozilla Firefox, classified under Origin Validation Error. CVSS score: 6.5/10. Published 2026-03-10.

How severe is CVE-2026-3846?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Mozilla Firefox

CVE-2026-3846

Same-origin policy bypass in the CSS Parsing and Computation component. This vulnerability was fixed in Firefox 148.0.2.

Published 2026-03-10 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.002 (4.9th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 5th percentile — 4.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.001 · newest: 0.002 · change: +0.001

Affected products

Mozilla Firefox — versions 148.0.2

Weakness classification (CWE)

CWE-346 — Origin Validation Error

References

bugzilla.mozilla.org/show_bug.cgi (Permissions Required)
www.mozilla.org/security/advisories/mfsa2026-19/ (Vendor Advisory)

Frequently asked questions

What is CVE-2026-3846?: CVE-2026-3846 is a medium-severity vulnerability in Mozilla Firefox, classified under Origin Validation Error. CVSS score: 6.5/10. Published 2026-03-10.
How severe is CVE-2026-3846?: Medium severity. CVSS v3 base score is 6.5 out of 10.