Protecting your web server against anonymous access

Here?s a sure-fire method to protect any kind of server that supports anonymous user access.



There's a sure-fire method to protect any kind of server that supports anonymous user access -- which means that this tip applies to FTP and other anonymous services, as well as Web servers that permit anonymous access. In such cases, the safest course of action is to isolate file system containers where anonymous access is permitted from containers where more stringent access controls apply.

This helps avoid the famous "root level" file container access problem, where allowing anonymous users access to the root of a logical drive or disk partition somehow magically confers access to other areas in a file system. The interesting thing about this problem is that it bedevils numerous operating systems, including various versions of Linux and Unix, as well as Windows.

In terms of best practices for enacting proper insulation and isolation techniques, consider the following strategies:
  • Create separate partitions or logical volumes within which anonymous access is permitted to occur. Make sure the "virtual root" (what anonymous Web or FTP users see as the root of the file system that they can access) is situated at least one level down in the file system hierarchy (thus C:/root is safe, while C:/ is not).
  • Set permissions explicitly to permit anonymous access from the virtual root on down in the anonymous container.
  • Explicitly deny access to the root of the anonymous container and to all other containers on systems where anonymous access is permitted.

    By following these approaches you isolate anonymous users to the containers where they should be allowed access anyway. You also insulate other containers from unauthorized access through anonymous accounts. It's a win-win situation! As always, feel free to e-mail me with feedback, comments or questions at etittel@lanw.com.

    About the author
    Ed Tittel is a principal at a content development company based in Austin, Texas, and the creator of the Exam Cram series. He has worked on numerous certification titles on Microsoft, Novell, CIW and Sun related topics; he's working on several security certification books in 2002 (ICSA, CISSP and more). As an expert on searchSecurity, Ed answers your questions on infosec certification and training.


  • This was first published in January 2002
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