Nextcloud is an open source content collaboration platform. In Nextcloud Server from versions 32.0.0 to before 32.0.9, and 33.0.0 to before 33.0.3, with the knowledge of other users’ principal URL an attacker could possibly send a request to gain full access to their calendar. Therefore, the attacker must be an authenticated user. This is because of improper authorization controls in the backend of the calendar. If the attacker had access to the calendar, they would be able to view and modify it. It is recommended that the Nextcloud Server is upgraded to 33.0.3 or 32.0.9. It is recommended that the Nextcloud Enterprise Server is upgraded to 33.0.3, 32.0.9, 31.0.14.5, 30.0.17.9, 29.0.16.16, 28.0.14.17, 27.1.11.26, 26.0.13.26, 25.0.13.29, 24.0.12.34, 23.0.12.35, 22.2.10.39, or 21.0.9.23
Nextcloud server is a self hosted personal cloud system. In affected versions OAuth codes did not expire. When an attacker would get access to an authorization code they could authenticate at any time using the code. As of version 28.0.0 OAuth codes are invalidated after 10 minutes and will no longer be authenticated. To exploit this vulnerability an attacker would need to intercept an OAuth code from a user session. It is recommended that the Nextcloud Server is upgraded to 28.0.0. There are no known workarounds for this vulnerability.