The blog post page contains the following link, which returns to the home page of the blog:
<a href='#' onclick='returnURL' = /url=https?:\/\/.+)/.exec(location); if(returnUrl)location.href = returnUrl[1];else location.href = "/"'>Back to Blog</a>
The url parameter contains an open redirection vulnerability that allows you to change where the "Back to Blog" link takes the user. To solve the lab, construct and visit the following URL, remembering to change the URL to contain your lab ID and your exploit server ID:
https://YOUR-LAB-ID.web-security-academy.net/post?postId=4&url=https://YOUR-EXPLOIT-SERVER-ID.exploit-server.net/
