Before version 4.8.2, WordPress was susceptible to a Cross-Site Scripting attack in the link modal via a javascript: or data: URL.
https://www.debian.org/security/2017/dsa-3997
https://wordpress.org/news/2017/09/wordpress-4-8-2-security-and-maintenance-release/
https://core.trac.wordpress.org/changeset/41393