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Part IV: Hacking Operating Systems
chkconfig
If you don’t have an inetd.conf file (or it’s empty), your version of Linux is
probably running the xinetd program (www.xinetd.org) — a more secure
replacement for inetd — to listen for incoming network application requests.
You can edit the /etc/xinetd.conf file if this is the case. For more information
on the usage of xinetd and xinetd.conf, enter man xinetd or man
xinetd.conf at a Linux command prompt. If you’re running Red Hat 7.0 or
later, you can run the /sbin/chkconfig program to turn off the daemons
you don’t want to load.
You can also enter chkconfig --list at a command prompt to see what services
are enabled in the xinetd.conf file.
If you want to disable a specific service, say snmp, enter the following:
chkconfig --del snmpd
You can use the chkconfig program to disable other services, such as FTP,
telnet, and web server.
Access control
TCP Wrappers can control access to critical services that you run, such as
FTP or HTTP. This program controls access for TCP services and logs their
usage, helping you control access via hostname or IP address and track malicious
activities.
You can find more information about TCP Wrappers from http://protect.
iu.edu/cybersecurity/tcp-wrappers.
Always make sure that your operating system and the applications running
on it are not open to the world (or your internal network) by ensuring that
reasonable password requirements are in place. Don’t forget to disable anonymous
FTP unless you absolutely need it. Even if you do, limit system access to
only those with a business need to access sensitive information.
Securing the .rhosts and hosts.equiv Files
Linux — and all the flavors of UNIX — are file-based operating systems.
Practically everything that’s done on the system involves the manipulation of
files. This is why so many attacks against Linux are at the file level.