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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tarpit may actually be illegal in some places. Read the La Brea story at http://www.

hackbusters.net/.

Caches, Proxies, and Load Balancers

A proxy is a man in the middle. A caching proxy is a man in the middle with a mem-

ory. All the security issues of email apply to web pages as they stream about: they

can be read, copied, forged, stolen, etc. The usual answer is to apply end-to-end

cryptography.

If you use sessions that are linked to a specific server (stored in temporary files or

shared memory rather than a database), you must somehow get every request with

the same session ID directed to the same server. Some load balancers offer session

affinity to do this. Without it, you’ll need to store the sessions in some shared

medium, such as an NFS-mounted filesystem or a database.

Layers of Defense

Test your setup with a vulnerability scanner. The best open source tool is nessus

(http://www.nessus.org), which includes tests for buffer overflows, bad Apache con-

figurations, buggy CGI scripts, and many other problems. It includes tests from nikto

(http://www.cirt.net/code/nikto.shtml)andlibwhisker (http://www.wiretrip.net/rfp/p/

doc.asp/i2/d21.htm), which can also be run on their own.

When you’re ready for production, use multiple levels of protection:

• Firewall (Chapter 2)