Hi,

We recently commissioned a third-party security audit of our application, 
and one of the findings was this:

Cross-Site Redirection (Medium Impact, Moderate Difficulty in exploiting)

If one pastes this string into the browser https://*cas.mydomain.com*
/cas/login?TARGET=https://yahoo.com

then, after authentication, the browser is redirected without complaint to 
yahoo.com.

The report said in detail:

"The application was found to take a URL as a parameter to determine where 
to direct the user. <Consultant> found that this URL can be any value 
allowing an attacker to insert a malicious URL that can be used to redirect 
to an external site before or after authentication.

A link to the login page, containing this URL could therefore be created, 
which can then be sent to a victim (e.g. as an email phishing attack). When 
the victim accesses this link, they are initially sent to the valid site. 
After authentication they can be redirected to a third party site without 
their knowledge.

This second site could be under the control of an attacker, and perform 
such actions as re-requesting their authentication details and performing a 
man-in-the-middle attack between the victim and the client's site, 
ultimately giving the attacker authenticated access to the application."

My questions are:
1. Is this a security hole in CAS as suggested by the security auditor?
2. Is there a workaround that we can implement?

Regards,
Ganesh

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