Umbraco is a free and open source .NET content management system. Starting in version 14.0.0 and prior to versions 14.3.2 and 15.1.2, it's possible to determine whether an account exists based on an analysis of response codes and timing of Umbraco management API responses. Versions 14.3.2 and 15.1.2 contain a patch. No known workarounds are available.
CWE-200, CWE-203