Englesystem is a shift planning system for chaos events. Engelsystem prior to v3.4.1 performed insufficient validation of user supplied data for the DECT number, mobile number, and work-log comment fields. The values of those fields would be displayed in corresponding log overviews, allowing the injection and execution of Javascript code in another user's context. This vulnerability enables an authenticated user to inject Javascript into other user's sessions. The injected JS will be executed during normal usage of the system when viewing, e.g., overview pages. This issue has been fixed in version 3.4.1.