- Comments: Prevent users who can not see a post from seeing comments on it.
- Shortcodes: Restrict media shortcode ajax to certain type.
- REST API: Ensure no-cache headers are sent when methods are overridden.
- REST API: Limit `search_columns` for users without `list_users`.
- Prevent unintended behavior when certain objects are unserialized.
- Application Passwords: Prevent the use of some pseudo protocols in application passwords.
Merges [56833], [56834], [56835], [56836], [56837], and [56838] to the 5.6 branch.
Props xknown, jorbin, Vortfu, joehoyle, timothyblynjacobs, peterwilsoncc, ehtis, tykoted, martinkrcho, paulkevan, dd32, antpb, rmccue.
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