What Makes a Network Vulnerable?

Up to now, we have reviewed network concepts with very little discussion of their security implications. But our earlier discussion of threats and vulnerabilities, as well as outside articles and your own experiences, probably have you thinking about the many possible attacks against networks. This section describes some of the threats you have already hypothesized and perhaps presents you with some new ones. But the general thrust is the same: threats aimed to compromise confidentiality, integrity, or availability, applied against data, software, and hardware by nature, accidents, nonmalicious humans, and malicious attackers.

Anonymity. An attacker can mount an attack from thousands of miles away and never come into direct contact with the system, its administrators, or users. The potential attacker is thus safe behind an electronic shield. The attack can be passed through many other hosts in an effort to disguise the attack's origin. And computer-to-computer authentication is not the same for computers as it is for humans secure distributed authentication requires thought and attention to detail.

Many points of attack—both targets and origins. A simple computing system is a self-contained unit. Access controls on one machine preserve the confidentiality of data on that processor. However, when a file is stored in a network host remote from the user, the data or the file itself may pass through many hosts to get to the user. One host's administrator may enforce rigorous security policies, but that administrator has no control over other hosts in the network. Thus, the user must depend on the access control mechanisms in each of these systems. An attack can come from any host to any host, so that a large network offers many points of vulnerability.

Sharing. Because networks enable resource and workload sharing, more users have the potential to access networked systems than on single computers. Perhaps worse, access is afforded to more systems, so that access controls for single systems may be inadequate in networks.

Unknown perimeter. A network's expandability also implies uncertainty about the network boundary. One host may be a node on two different networks, so resources on one network are accessible to the users of the other network as well. Although wide accessibility is an advantage, this unknown or uncontrolled group of possibly malicious users is a security disadvantage. A similar problem occurs when new hosts can be added to the network. Every network node must be able to react to the possible presence of new, untreatable hosts