The external legacy SMB storage (not using php-libsmbclient) of ownCloud was not properly neutralizing all special elements which allows an adversary to execute arbitrary SMB commands.
Effectively this allows an attacker to gain access to any file on the system or overwrite it, potentially leading to a PHP code execution.
The vulnerable library is now properly handling potentially dangerous characters.
The ownCloud team thanks the following people for their research and responsible disclosure of the above advisory: