Nextcloud Server before 9.0.54 and 10.0.1 & ownCloud Server before 9.1.2, 9.0.6, and 8.2.9 suffer from SMB User Authentication Bypass. Nextcloud/ownCloud include an optional and not by default enabled SMB authentication component that allows authenticating users against an SMB server. This backend is implemented in a way that tries to connect to a SMB server and if that succeeded consider the user logged-in. The backend did not properly take into account SMB servers that have any kind of anonymous auth configured. This is the default on SMB servers nowadays and allows an unauthenticated attacker to gain access to an account without valid credentials. Note: The SMB backend is disabled by default and requires manual configuration in the Nextcloud/ownCloud config file. If you have not configured the SMB backend then you're not affected by this vulnerability.

ownCloud Server before 8.2.12, 9.0.x before 9.0.10, 9.1.x before 9.1.6, and 10.0.x before 10.0.2 are vulnerable to XSS on error pages by injecting code in url parameters.

Nextcloud Server before 10.0.1 & ownCloud Server before 9.0.6 and 9.1.2 suffer from Reflected XSS in the Gallery application. The gallery app was not properly sanitizing exception messages from the Nextcloud/ownCloud server. Due to an endpoint where an attacker could influence the error message, this led to a reflected Cross-Site-Scripting vulnerability.

Nextcloud Server before 10.0.1 & ownCloud Server before 9.0.6 and 9.1.2 suffer from Stored XSS in CardDAV image export. The CardDAV image export functionality as implemented in Nextcloud/ownCloud allows the download of images stored within a vCard. Due to not performing any kind of verification on the image content this is prone to a stored Cross-Site Scripting attack.

Nextcloud Server before 9.0.54 and 10.0.1 & ownCloud Server before 9.0.6 and 9.1.2 suffer from content spoofing in the dav app. The exception message displayed on the DAV endpoints contained partially user-controllable input leading to a potential misrepresentation of information.

Nextcloud Server before 9.0.54 and 10.0.1 & ownCloud Server before 9.0.6 and 9.1.2 suffer from content spoofing in the files app. The location bar in the files app was not verifying the passed parameters. An attacker could craft an invalid link to a fake directory structure and use this to display an attacker-controlled error message to the user.