Icinga Web 2 is an open source monitoring web interface, framework and command-line interface. A vulnerability in versions prior to 2.11.5 and 2.12.13 allows an attacker to craft a request that, once transmitted to a victim's Icinga Web, allows to embed arbitrary Javascript into it and to act on behalf of that user. This issue has been resolved in versions 2.11.5 and 2.12.3 of Icinga Web 2. As a workaround, those who have Icinga Web 2.12.2 may enable a content security policy in the application settings. Any modern browser with a working CORS implementation also sufficiently guards against the vulnerability.