XWiki Platform web templates vulnerable to reflected XSS in the create document form if name validation is enabled

XWiki Platform is a generic wiki platform offering runtime services for applications built on top of it. When document names are validated according to a name strategy (disabled by default), XWiki starting in version 12.0-rc-1 and prior to versions 12.10.12 and 15.5-rc-1 is vulnerable to a reflected cross-site scripting attack in the page creation form. This allows an attacker to execute arbitrary actions with the rights of the user opening the malicious link. Depending on the rights of the user, this may allow remote code execution and full read and write access to the whole XWiki installation. This has been patched in XWiki 14.10.12 and 15.5-rc-1 by adding appropriate escaping. The vulnerable template file `createinline.vm` is part of XWiki's WAR and can be patched by manually applying the changes from the fix.