Novell LINUX ENTERPRISE SERVER 10 SP2 - INSTALLATION AND ADMINISTRATION Installation Manual page 908

the user) uses up some more space than what is available in the buffer. As a result, data
is written beyond the end of that buffer area, which, under certain circumstances, makes
it possible for a program to execute program sequences influenced by the user (and not
by the programmer), rather than just processing user data. A bug of this kind may have
serious consequences, especially if the program is being executed with special privileges
(see Section 49.1.4, "File Permissions" (page 888)).
Format string bugs work in a slightly different way, but again it is the user input that
could lead the program astray. In most cases, these programming errors are exploited
with programs executed with special permissions—setuid and setgid programs—which
also means that you can protect your data and your system from such bugs by removing
the corresponding execution privileges from programs. Again, the best way is to apply
a policy of using the lowest possible privileges (see Section 49.1.4, "File Permissions"
(page 888)).
Given that buffer overflows and format string bugs are bugs related to the handling of
user data, they are not only exploitable if access has been given to a local account.
Many of the bugs that have been reported can also be exploited over a network link.
Accordingly, buffer overflows and format string bugs should be classified as being
relevant for both local and network security.
49.1.6 Viruses
Contrary to what some people say, there are viruses that run on Linux. However, the
viruses that are known were released by their authors as a proof of concept to prove
that the technique works as intended. None of these viruses have been spotted in the
wild so far.
Viruses cannot survive and spread without a host on which to live. In this case, the host
would be a program or an important storage area of the system, such as the master boot
record, which needs to be writable for the program code of the virus. Owing to its
multiuser capability, Linux can restrict write access to certain files, especially important
with system files. Therefore, if you did your normal work with root permissions, you
would increase the chance of the system being infected by a virus. In contrast, if you
follow the principle of using the lowest possible privileges as mentioned above, chances
of getting a virus are slim.
Apart from that, you should never rush into executing a program from some Internet
site that you do not really know. SUSE Linux Enterprise's RPM packages carry a
890 Installation and Administration