Insufficient sanitization of user provided rsync command in SFTPGo

SFTPGo is an open source, event-driven file transfer solution. SFTPGo supports execution of a defined set of commands via SSH. Besides a set of default commands some optional commands can be activated, one of them being `rsync`. It is disabled in the default configuration and it is limited to the local filesystem, it does not work with cloud/remote storage backends. Due to missing sanitization of the client provided `rsync` command, an authenticated remote user can use some options of the rsync command to read or write files with the permissions of the SFTPGo server process. This issue was fixed in version v2.6.5 by checking the client provided arguments. Users are advised to upgrade. There are no known workarounds for this vulnerability.