org.xwiki.platform:xwiki-platform-oldcore may leak data through deleted and re-created documents

XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. Starting in version 9.4-rc-1 and prior to versions 14.10.8 and 15.3-rc-1, when a document has been deleted and re-created, it is possible for users with view right on the re-created document but not on the deleted document to view the contents of the deleted document. Such a situation might arise when rights were added to the deleted document. This can be exploited through the diff feature and, partially, through the REST API by using versions such as deleted:1 (where the number counts the deletions in the wiki and is thus guessable). Given sufficient rights, the attacker can also re-create the deleted document, thus extending the scope to any deleted document as long as the attacker has edit right in the location of the deleted document. This vulnerability has been patched in XWiki 14.10.8 and 15.3 RC1 by properly checking rights when deleted revisions of a document are accessed. The only workaround is to regularly clean deleted documents to minimize the potential exposure. Extra care should be taken when deleting sensitive documents that are protected individually (and not, e.g., by being placed in a protected space) or deleting a protected space as a whole.