SSRF is an exploit using the *shortcoming of URL Parsing#* from the targeted server to access internal service, which should not be accessible from the outside world, by passing arbitrary commands to that service embedded with the URL parameter. The attacker could use the server as a proxy to request services from the supposedly internal processes. They could smuggle protocols such as SMTP, File Transfer Protocol (FTP), HTTP and Redis within the URL.
Some protocols such as Gopher# is extremely vulnerable to the SSRF attack.
To prevent SSRF, improve the security on application and network layer. On application layer, avoid reusing input URL provided by user (ignore the parameter upon the parsing error), instead use only the IP Address and hostname for connection. On network layer, setup firewall or NetWork to block the incoming traffics that try to access internal services.