What is CVE-2020-12404?

CVE-2020-12404 is a medium-severity vulnerability in Mozilla Firefox, classified under Cross-site Scripting. CVSS score: 4.3/10. Published 2020-07-09.

How severe is CVE-2020-12404?

Medium severity. CVSS v3 base score is 4.3 out of 10.

XSS in Mozilla Firefox

CVE-2020-12404

For native-to-JS bridging the app requires a unique token to be passed that ensures non-app code can't call the bridging functions. That token could leak when used for downloading files. This vulnerability affects Firefox for iOS < 26.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2020-07-09 · last modified 2026-08-19.

CVSS v3 metric

CVSS v3 base score 4.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N.

EPSS exploit prediction

EPSS: 0.008 (54.5th percentile), scored 2026-10-03.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 54th percentile — 54.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000

Affected products

Mozilla Firefox
Mozilla Firefox For iOS — versions unspecified
Mozilla Firefox Mobile

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

References

www.mozilla.org/security/advisories/mfsa2020-19/ (Vendor Advisory)
bugzilla.mozilla.org/show_bug.cgi (Permissions Required, Issue Tracking, Vendor Advisory)

Frequently asked questions

What is CVE-2020-12404?: CVE-2020-12404 is a medium-severity vulnerability in Mozilla Firefox, classified under Cross-site Scripting. CVSS score: 4.3/10. Published 2020-07-09.
How severe is CVE-2020-12404?: Medium severity. CVSS v3 base score is 4.3 out of 10.