XWiki is a generic wiki platform. In versions starting from 1.8 and prior to 15.10.16, 16.4.6, and 16.10.1, it is possible for a remote unauthenticated user to escape from the HQL execution context and perform a blind SQL injection to execute arbitrary SQL statements on the database backend, including when "Prevent unregistered users from viewing pages, regardless of the page rights" and "Prevent unregistered users from editing pages, regardless of the page rights" options are enabled. Depending on the used database backend, the attacker may be able to not only obtain confidential information such as password hashes from the database, but also execute UPDATE/INSERT/DELETE queries. This issue has been patched in versions 16.10.1, 16.4.6 and 15.10.16. There is no known workaround, other than upgrading XWiki.