WordPress before 5.5.2 mishandles embeds from disabled sites on a multisite network, as demonstrated by allowing a spam embed.
https://www.debian.org/security/2020/dsa-4784
https://wordpress.org/news/2020/10/wordpress-5-5-2-security-and-maintenance-release/
https://lists.debian.org/debian-lts-announce/2020/11/msg00004.html