XWiki Platform is a generic wiki platform. Prior to 15.10.14, 16.4.6, and 16.10.0-rc-1, protected pages are listed when requesting the REST endpoints /rest/wikis/[wikiName]/pages even if the user doesnt have view rights on them. Its particularly true if the entire wiki is protected with Prevent unregistered user to view pages: the endpoint would still list the pages of the wiki, though only for the main wiki. The problem has been patched in XWiki 15.10.14, 16.4.6, 16.10.0RC1. In those versions the endpoint can still be requested but the result is filtered out based on pages rights.
The product makes resources available to untrusted parties when those resources are only intended to be accessed by the product.