The Goobi viewer is a web application that allows digitised material to be displayed in a web browser. From version 4.11.0 to before version 26.05, several Jakarta WebSocket endpoints in goobi-viewer-core (DownloadTaskEndpoint, CampaignEndpoint, AutocompleteEndpoint, UserEndpoint) accept connections without verifying that the associated HttpSession belongs to a logged-in user, and none validate the Origin header against an allowlist. An unauthenticated attacker can therefore connect to these endpoints; through CampaignEndpoint this allows polluting the in-process crowdsourcing page-lock map and broadcasting forged lock messages, disrupting reviewers' work. This issue has been patched in version 26.05.