Custom log-in and log-out locations are used-defined as jslob but were not checked to contain malicious protocol handlers. 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 jslob content for those locations to avoid redirects to malicious content. No publicly available exploits are known.
