Class User Enumeration CVE Remote Yes Credit n4xh4ck5 Home https://github.com/n4xh4ck5 Vulnerable Owncloud Server 8.1 to 10.0 Once time authenticated in the application, the Owncloud funcionality let to User enumeration due the different error messages of the server. The vulnerabiblity it finds in Owncloud Server 8.1 to 10.0. In the next steps it describes the PoC to show the vulnerability: - Go to the user settings. - Analyzing the traffic, it can be appreciated the next URL (In this case I used to demo.owcloud.org such as target trought Bug Bounty program Hacker One): https://demo.owncloud.org/index.php/avatar/demo/1 The server responds: "{"data"}: ("displayname":"demo")} So, if it changes in the URL the value "demo" by another: For example, by a valid user such as admin: https://demo.owncloud.org/index.php/avatar/admin/1 The server responds: "{"data"}: ("displayname":"admin")} but it changes by a user not valid such as "noexiste": https://demo.owncloud.org/index.php/avatar/noexiste/1 the server responds: "{"data"}: ("displayname":"")} The server responds differently depending on the legitimacy of the user, it is possible to enumerate users. Kind regards. Thanks for you job.