XWiki OIDC has various tools to manipulate OpenID Connect protocol in XWiki. Starting in version 2.17.1 and prior to version 2.18.2, anyone with VIEW access to a user profile can create a token for that user. If that XWiki instance is configured to allow token authentication, it allows authentication with any user (since users are very commonly viewable, at least to other registered users). Version 2.18.2 contains a patch. As a workaround, disable token access.