| Red Hat Linux 7.1: The Official Red Hat Linux Reference Guide |
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If you use your Red Hat Linux system on a network (such as a local area network, wide area
network, or the Internet), you must be aware that your system is at a
greater degree of risk than if you were not connected to that
network. Beyond brute attacks on password files and users having
inappropriate access, the presence of your system on a larger network
widens the opportunity for a security problem and the possible form it
may appear.
A number of network security measures have been built into Red Hat Linux, and
many open source security tools are also included with the primary
distribution. However, despite your preparedness, network security
problems may occur, due in part to your network topology or a dozen
other factors. To help you determine the source and method of a network
security problem, consider the the most likely ways such a problem can occur:
Sniffing for authentication data — Many
default authentication methods in Linux and other operating systems
depend on sending your authentication information "in the clear," where your
username and password is sent over the network in plain text or unencrypted. Tools are
widely available for those with access to your network (or the
Internet, if you are accessing your system using it) to "sniff" or
detect your password by recording all data transferred over the
network and sifting through it to find common login statements. This
method can be used to find any information you send unencrypted,
even your root password. It is imperative that you implement and utilize tools like
Kerberos 5 and OpenSSH to prevent passwords and other
sensitive data form being sent without encryption. If, for whatever
reason, these tools cannot be used with your system, then definitely
never log in as root unless you are at the console.
Frontal attack — Denial of Service (DoS)
attacks and the like can cripple even a secure system by flooding it
with improper or malformed requests that overwhelm it or create
processes that put your system and its data, as well as other
systems that communicate with it, at risk. A number of different protections are
available to help stop the attack and minimize the damage, such as
packet-filtering firewalls. However, frontal attacks are best
handled with a comprehensive look at ways in which untrusted systems
communicate with your trusted systems, putting protective barriers
between the two, and developing a way to quickly respond to any
event so that the disruption and possible damage is limited.
Exploiting a security bug or loophole —
Occasionally, bugs are found in software that, if exploited, could
do grievous damage to an unprotected system. For that reason, run as
few processes as root as possible. Also, use the various tools
available to you, such as the Red Hat Network for package updates and security
alerts, to fix security problems as soon as they are discovered. Also,
make sure that your system has no unnecessary programs starting up
at boot time. The fewer programs you have started, the fewer possible
security bugs can affect you.
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