Linux Server Security, Second Edition

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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Chapter 10: Securing Web Servers

Strengthen

Never trust user input. Secure access to external files and programs.

Diversify

Use layers of protection. Don’t rely on security by obscurity of a single mecha-

nism, such as a password.

Document

Write down what you’ve done because you won’t remember it. Honest.

The Web Server

A secure web service starts with a secure web server, which in turn starts with good

code—no buffer overflows or other problems that could be exploited to gain root

privileges. Apache has had a handful of critical vulnerabilities over the past few years,

and has generally released fixed versions promptly. Apache powers about two-thirds

of the 55 million hosts in the monthly Netcraft survey (http://news.netcraft.com/

archives/web_server_survey.html).

Microsoft’s Internet Information Server (IIS), with less than a third of Apache’s mar-

ket share, has had many critical and ongoing security problems. A Microsoft Secu-

rity Bulletin issued in April 2002 described 10 critical problems in IIS 4 and 5. These

include vulnerabilities to buffer overruns, Denial of Service, and cross-site scripting;

a number of these provide full-system privileges to the attacker. IIS 6 is reportedly

better.

In practice, most Apache security problems are caused by configuration errors, and

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