🟡 XWiki Platform vulnerable to document deletion and overwrite from edit (xwiki xwiki-platform)

Description

XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. When a user has view but not edit right on a page in XWiki, that user can delete the page and replace it by a page with new content without having delete right. The previous version of the page is moved into the recycle bin and can be restored from there by an admin. As the user is recorded as deleter, the user would in theory also be able to view the deleted content, but this is not directly possible as rights of the previous version are transferred to the new page and thus the user still doesn't have view right on the page. It therefore doesn't seem to be possible to exploit this to gain any rights. This has been patched in XWiki 14.10.21, 15.5.5 and 15.10.6 by cancelling save operations by users when a new document shall be saved despite the document's existing already.