The remote host is vulnerable to a buffer overflow.
The remote host is using a vulnerable version of PuTTY, a SSH client built for Linux and UNIX variants as well as Microsoft Windows operating systems. This version of PuTTY does not properly handle an integer value passed from the SSH Server during an SFTP connection. An attacker exploiting this flaw would need to be able to convince a user to use PuTTY to initiate an SFTP connection to a malicious SSH server. Successful exploitation would result in PuTTY crashing or possibly executing arbitrary commands.
Upgrade to PuTTY 0.57 or higher.