What is CVE-2020-12390?

CVE-2020-12390 is a critical-severity vulnerability in Mozilla Firefox, classified under Deserialization of Untrusted Data. CVSS score: 9.8/10. Published 2020-05-26.

How severe is CVE-2020-12390?

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

Deserialization in Mozilla Firefox

CVE-2020-12390

Incorrect origin serialization of URLs with IPv6 addresses could lead to incorrect security checks. This vulnerability affects Firefox < 76.

Vulnerability class: Insecure Deserialization

Published 2020-05-26 · 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: 0.016 (74.7th percentile), scored 2026-10-03.

Low probability of exploitation in the next 30 days, but still tracked. 75th percentile — 74.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.016 · newest: 0.016 · change: 0.000

Affected products

Mozilla Firefox — versions unspecified

Weakness classification (CWE)

CWE-502 — Deserialization of Untrusted Data

References

www.mozilla.org/security/advisories/mfsa2020-16/ (Vendor Advisory)
bugzilla.mozilla.org/show_bug.cgi (Permissions Required)

Frequently asked questions

What is CVE-2020-12390?: CVE-2020-12390 is a critical-severity vulnerability in Mozilla Firefox, classified under Deserialization of Untrusted Data. CVSS score: 9.8/10. Published 2020-05-26.
How severe is CVE-2020-12390?: Critical severity. CVSS v3 base score is 9.8 out of 10.