public with sharing class classexample {
    public classexample() {
         c= new contact();  
         paramMap = apexpages.currentpage().getparameters();      
         list1 = new List<String>(paramMap.keySet());
         for(integer i=0;i<list1.size();i++){
              paramName = list1.get(i);
              paramValue = paramMap.get(paramName);
              if(paramName != 'returnUrl' && paramName !='core.apexpages.devmode.url'){
              c.put(paramName,paramValue);
              }         
            }   
         returnUrl = apexpages.currentpage().getparameters().get('returnUrl');  

    }

public contact c;
public string lastname{get;set;}
public string firstname{get;set;}
public string paramName{get;set;}
public string paramValue{get;set;}
public List<String> list1{get;set;}
public  map<string,string> paramMap{get;set;}
public  string returnUrl;
   
   
    public pagereference autorun() {  
           
      if(c.lastname!=null){     
       insert c;
       }
       if(returnUrl!=null){
      pagereference p = new pagereference(returnUrl);  
      return p;
      }else{
          return null;
      }

      
     
  }
  }

 Hi to all,

in the above class  there are two security issues.

1. returnUrl = apexpages.currentpage().getparameters().get('returnUrl'); 

and 

2.

pagereference p = new pagereference(returnUrl);
return p;

here Security issue is

"

 Open Redirect Vulnerability

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."

how to fix these issues, please help me, its urgent,

Thanking you inadvance.