ActFax FTP Server Post Auth 'RETR' Command Denial of Service Vulnerability

The host is running ActFax FTP Server and is prone to denial of service vulnerability.
Successful exploitation will allow the remote attackers to cause a denial of service. Impact Level: Application
No solution or patch was made available for at least one year since disclosure of this vulnerability. Likely none will be provided anymore. General solution options are to upgrade to a newer release, disable respective features, remove the product or replace the product by another one.
The flaw is due to an error while parsing RETR command, which can be exploited to crash the FTP service by sending big parameter to 'RETR' command.
ActiveFax Version 4.25 (Build 0221), Other versions may also be affected.