OpenProject is an open-source, web-based project management software. In the new editor for collaborative documents based on BlockNote, OpenProject maintainers added a custom extension in OpenProject version 17.0.0 that allows to mention OpenProject work packages in the document. To show work package details, the editor loads details about the work package via the OpenProject API. For this API call, the extension to the BlockNote editor did not properly validate the given work package ID to be only a number. This allowed an attacker to generate a document with relative links that upon opening could make arbitrary `GET` requests to any URL within the OpenProject instance. This issue was patched in version version 0.0.22 of op-blocknote-extensions, which was shipped with OpenProject 17.0.2. If users cannot update immediately to version 17.0.2 of OpenProject, administrators can disable collaborative document editing in Settings -> Documents -> Real time collaboration -> Disable.