CVE-2016-5284: Mozilla Firefox

High severity, CVSS 7.4. EPSS: 2.4% chance of exploitation in the next 30 days.

Mozilla Firefox before 49.0, Firefox ESR 45.x before 45.4, and Thunderbird < 45.4 rely on unintended expiration dates for Preloaded Public Key Pinning, which allows man-in-the-middle attackers to spoof add-on updates by leveraging possession of an X.509 server certificate for addons.mozilla.org signed by an arbitrary built-in Certification Authority.

Affected products

• Mozilla Firefox: up to and including 48.0.2; version 45.0 only; version 45.0.1 only; version 45.0.2 only; version 45.1.1 only; version 45.2.0 only; …

Published 2016-09-22. Last modified 2026-06-17.