LinuxServer Changes:
Rebase to Alpine 3.14.
bookstack Changes:
Security Release
BookStack v21.10.2 has been released. This is a security release that builds upon changes in v21.10.1 which covers a vulnerability which would allow malicious users, who have permission to update or create pages, to upload content that could then be utilized for phishing or other general malicious intent.
If you allow untrusted users to edit page content you should update as soon as possible.