There have been numerous exploits and security breaches for IIS that allow a remote user to navigate the directory structure under a Web site completely unencumbered. Usually, this means that any file and folder underneath a Web site is potentially available for downloading or even deletion or alteration.
If the thought of a remote user being able to download your entire Web server's file structure or even alter the content offered through your Web sites doesn't scare you, then maybe this will: Mapped directories from your Web server to other networked servers potentially grant unrestricted access to those systems, as well.
This problem is not limited to IIS Web servers, but can be an issue on any vendor's Web server. Clearly stated, the problem is this: If your Web server's security is compromised and a user is able to navigate the Web root without access restrictions, then they can access any folder mapped under that Web root. Many server operating systems, and even Web servers themselves, offer the ability to create virtual directories or mapped points. A virtual directory or a mapped point is a folder that acts as a redirector to a shared folder on another system.
The only way to prevent a Web server security breach from compromising your entire network is to completely avoid using virtual directories or mapped points. You should consider a Web server an entity that needs to be quarantined. It should be separated from your internal network completely. You should grant only a few users one-way access to the Web server from the internal network (i.e. to upload new files to the Web server). If you need a resource to be accessible via the Web, make a copy of it onto the Web server; do not map a drive from the Web server back to its internal network home.
About the author
James Michael Stewart is a researcher and writer for Lanwrights, Inc.