SysAdmin: Linux Intrusion Detection

“No matter how security minded you are, no matter how many
updates and patches you apply, there’s always a chance that someone
will crack one of your systems. It’s an unpleasant reality, but
it’s a fact: no system is 100% secure unless it’s turned off, but
how useful is that? Although it’s important to spend time on
prevention, you must also have a backup plan in the event that
security is compromised. If one of your systems is cracked,
immediate detection and damage control are essential to prevent an
intruder from gaining access to other systems and causing
irreparable problems.

“One key to intrusion detection is understanding the most common
security exploits. This knowledge will allow you to set up a
checklist for periodic security checks of your system. If you’re
running a DNS server, BIND is a favorite target for attack. BIND
has a number of security issues and should be disabled if not
needed. If you need BIND, be sure to check at least monthly for
updates and fixes. CGI scripts are another point of vulnerability.
If CGI can be avoided, it is probably best to do so. Under no
circumstances should an administrator leave sample CGI scripts on a
production server or run a Web server as root. The list of CGI
issues is too great to include here, but the SANS Top Ten List of
security threats contains useful tips about CGI and other
vulnerabilities. There’s no standard for how often these security
audits should be performed, but careful administrators continually
check for signs of intrusion. A comprehensive check should be
performed at least monthly, if not more frequently.”


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