An open redirect is an application that takes a parameter and redirects a user to the parameter value without any validation. This vulnerability is used in phishing attacks to get users to visit malicious sites without realizing it.
Likelihood of exploit
Avoidance and mitigation
To avoid the open redirect vulnerability parameters of the application script/program must be validated before sending 302 HTTP code (redirect) to the client browser.
The server must have a relation of the authorized redirections (i.e. in a database)