Authorization Bypass Through User-Controlled Key
Collabora Online is a collaborative online office suite. In versions prior to 4.2.17-1 and version 6.4.9-5, unauthenticated attackers are able to gain access to files which are currently opened by other users in the Collabora Online editor. For successful exploitation the attacker is required to guess the file identifier - the predictability of this file identifier is dependent on external file-storage implementations (this is a potential "IDOR" - Insecure Direct Object Reference - vulnerability). Versions 4.2.17-1 and 6.4.9-5 contain patches for this issue. There is no known workaround except updating the Collabora Online application to one of the patched releases.
CWE-639 - Authorization Bypass Through User-Controlled Key
The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.