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4.4 What are some common attacks, and how can I protect my system against them?

  Each site is a little different from every other in terms of what attacks are likely to be used against it. Some recurring themes do arise, though.

4.4.1 SMTP Server Hijacking (Unauthorized Relaying)

This is where a spammer will take many thousands of copies of a message and send it to a huge list of email addresses. Because these lists are often so bad, and in order to increase the speed of operation for the spammer, many have resorted to simply sending all of their mail to an SMTP server that will take care of actually delivering the mail.

Of course, all of the bounces, spam complaints, hate mail, and bad PR come for the site that was used as a relay. There is a very real cost associated with this, mostly in paying people to clean up the mess afterward.

The Mail Abuse Prevention SystemTM Transport Security InitiativeTM maintains a complete description of the problem, and how to configure about every mailer on the planet to protect against this attack.

4.4.2 Exploiting Bugs in Applications

Various versions of web servers, mail servers, and other Internet service software contain bugs that allow remote (Internet) users to do things ranging from gain control of the machine to making that application crash and just about everything in between.

The exposure to this risk can be reduced by running only necessary services, keeping up to date on patches, and using products that have been around a while.

4.4.3 Bugs in Operating Systems

Again, these are typically initiated by users remotely. Operating systems that are relatively new to IP networking tend to be more problematic, as more mature operating systems have had time to find and eliminate their bugs. An attacker can often make the target equipment continuously reboot, crash, lose the ability to talk to the network, or replace files on the machine.

Here, running as few operating system services as possible can help. Also, having a packet filter in front of the operating system can reduce the exposure to a large number of these types of attacks.

And, of course, chosing a stable operating system will help here as well. When selecting an OS, don't be fooled into believing that ``the pricier, the better''. Free operating systems are often much more robust than their commercial counterparts

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