CVE-2019-11747: Mozilla Firefox

Medium severity, CVSS 6.5. EPSS: 1.2% chance of exploitation in the next 30 days.

The "Forget about this site" feature in the History pane is intended to remove all saved user data that indicates a user has visited a site. This includes removing any HTTP Strict Transport Security (HSTS) settings received from sites that use it. Due to a bug, sites on the pre-load list also have their HSTS setting removed. On the next visit to that site if the user specifies an http: URL rather than secure https: they will not be protected by the pre-loaded HSTS setting. After that visit the site's HSTS setting will be restored. This vulnerability affects Firefox < 69 and Firefox ESR < 68.1.

Affected products

• Mozilla Firefox: before 69.0 (fixed in 69.0)
• Mozilla Firefox ESR: before 68.1.0 (fixed in 68.1.0)

Published 2019-09-27. Last modified 2026-06-17.