CVE-2018-5116: WebExtensions with the "ActiveTab" permission are able to access frames hosted within the active tab even if the frames are cross-origin.

Severity: Critical

CVSS Score: 9.8

WebExtensions with the "ActiveTab" permission are able to access frames hosted within the active tab even if the frames are cross-origin. Malicious extensions can inject frames from arbitrary origins into the loaded page and then interact with them, bypassing same-origin user expectations with this permission. This vulnerability affects Firefox < 58.