server config, <VirtualHost>, <Global>, <Anonymous>, <Directoryl>, .ftpaccess
1.2.0pre7 and later
AllowFilter allows the configuration of a regular expression that must be matched for all command arguments sent to ProFTPD. It is extremely useful in controlling what characters may be sent in a command to ProFTPD, preventing some possible types of attacks against ProFTPD. The regular expression is applied against the arguments to the command sent by the client, so care must be taken when creating a proper regex. Commands that fail the regex match result in a "Forbidden command" error being returned to the client. If the regular-expression argument contains whitespace, it must be enclosed in quotes.
# Only allow commands containing alphanumeric characters and whitespace AllowFilter "^[a-zA-Z0-9 ,]*$"