ASP.NET - Trust Level = Full?

Question

I recently joined a firm and when analyzing their environment I noticed that the SharePoint web.config had the trust level set to Full. I know this is an absolutely terrible practice and was hoping the stackoverflow community could help me outline the flaws in this decision.

Oh, it appears this decision was made to allow the developers to deploy dlls to the Bin folder without creating CAS policies. Sigh.

Just want to clarify and make matters worse, we are also deploying third party code to this web application.

Answer 1

Todd,

The book, "Programming Microsoft ASP.Net 3.5", by Dino Espisito provides some sound reasoning for not allowing Full Trust in ASP.Net applications.

Among other reasons, Dino states that web applications exposed to the internet are "one of the most hostile environments for computer security you can imagine." And:

a publicly exposed fully trusted application is a potential platform for hackers to launch attacks. The less an application is trusted, the more secure that application happens to be.

I'm surprised the StackOverflow community did not outline the problem with Full Trust better. I was hoping for the same thing so I didn't have to go digging through my pile of books to find the answer, lazy me.

Answer 2

If they're ignoring the CAS policies, it might be a tough sell to get them to dial it back, since it makes their job a little harder (or, at least, a little less forgiving). Changing security practices is always tough - like when I had to convince my boss that using the SA accounts in the SQL connection string of our web applications was a bad idea - but hang in there.

Full Trust allows the application to escalate to control of any resource on the computer. While you'd have to have a security flaw in your application to allow these, and they'll probably claim that they've prevented any escalations through astute programming, remind them that in the case that something happens, wouldn't they rather the web application didn't have control of the whole computer? I mean, just in case?

EDIT: I was a little overzealous with my language here. Full Trust would allow the application to control whatever it wants, but only if the Application Pool process has sufficient rights to do it. So if you're running as a limited user with no rights on the server except what the applicaition needs, then I suppose there's essentially no risk to "Full Trust". The reality is that the app pool owner most likely has a number of rights you wouldn't want your app to have (and in some cases, many, many more), so it's much safer to limit app security and grant additional rights needs individually to the application. Thanks for the correction, Barry.

Answer 3

Flaws? Many. But the most damning thing is straight out of the CAS utility:

"...it allows full access to your computer's resources such as the file system or network access, potentially operating outside the control of the security system."

That means, code granted Full Trust can execute any other piece of code (managed or otherwise) on the system, can call across the network to any machine, can do anything in the file system (including changing permissions on restricted files - even OS files).

Most web programmers would say "that's not a problem, it's just my code," which is fine.... until a security flaw crops up in their code that allows an attacker to use it to do unsavoury things. Then previously-granted Full Trust becomes quite unfortunate.