XWiki Platform: Privilege escalation from edit to script right through Live Data editing

XWiki Platform is a generic wiki platform. From 13.4-rc-1 until 16.10.17, 17.4.10, 17.10.4, and 18.1.0-rc-1, the Live Data edit REST API allows a user who can edit a page to change that page's rights without executing the normal document-saving authorization checks. The user can grant script right and then execute potentially dangerous Velocity scripts or send unfiltered HTML and JavaScript to clients. The same missing checks can circumvent extension security controls implemented as listeners for UserUpdatingDocumentEvent and related user document events. This issue is fixed in versions 16.10.17, 17.4.10, 17.10.4, and 18.1.0-rc-1.