Specifications

posted on the security mailing lists. They can be used to target the vulnera-
bility without knowing the details of the code. Over the years, experience has
shown that the availability of exploit codes has contributed to more secure
operating systems, obviously due to the fact that operating system makers
were forced to fix the problems in their software. With free software, anyone
has access to the source code (SuSE Linux comes with all available source
codes) and anyone who finds a vulnerability and its exploit code can submit
a patch to fix the corresponding bug.
DoS — Denial of Service
The purpose of this kind of attack is to force down a server program or even
an entire system, something which could be achieved by various means:
overloading the server, keeping it busy with garbage packets, or exploiting
a remote buffer overflow.
Often a DoS attack is done with the sole purpose of making the service dis-
appear. However, once a given service has become unavailable, communi-
cations could become vulnerable to so-called “man-in-the-middle attacks”
(sniffing, TCP connection hijacking, spoofing) and DNS poisoning, explained
below.
Man in the Middle: Sniffing, TCP Connection Hijacking, Spoofing
In general, any remote attack performed by an attacker who puts himself be-
tween the communicating hosts is called a “man-in-the-middle attack”. What
almost all types of man-in-the-middle attacks have in common is that the vic-
tim is usually not aware that there is something happening. There are many
possible variants, for example, the attacker could pick up a connection re-
quest and forward that to the target machine himself. Now the victim has
unwittingly established a connection with the wrong host, because the other
end is posing as the legitimate destination machine. The simplest form of a
man-in-the-middle attack is called “sniffer” — the attacker is “just” listening
to the network traffic passing by. As a more complex attack, the “man in the
middle” could try to take over an already established connection (hijacking).
To do so, the attacker would have to analyze the packets for some time to
be able to predict the TCP sequence numbers belonging to the connection.
When the attacker finally seizes the role of the target host, the victims will
notice this, because they get an error message saying the connection was ter-
minated due to a failure.
What often makes things easier for attackers is the fact that there are pro-
tocols which are not secured against hijacking through encryption, but only
perform a simple authentication procedure upon establishing the connection.
204 Security and Confidentiality