Frontend themes are defined by user-controllable jslob settings and could point to a malicious resource which gets processed during login. Malicious script code can be executed within the victims context. This can lead to session hijacking or triggering unwanted actions via the web interface and API. To exploit this an attacker would require temporary access to the users account or lure a user to a compromised account. We now sanitize the theme value and use a default fallback if no theme matches. No publicly available exploits are known.