Posted by arlene

The typical Internet client computer is an Intel PC, Macintosh, or desktop workstation, with a TCP/IP protocol stack and a variety of Internet client applications. (If the PC is running server applications, we will consider it to be a server.) There are two key client-security issues to consider: how does the attacker get at the client, and what does he or she do once there?

The following are potential methods of attack on client computers.

Physical Access to the Computer

Take a few minutes to wander around your company’s offices. Count the unattended computers. If machines are left logged in but unattended at night, they are accessible to the cleaning staff and whoever else has physical access at night. Even if unattended machines are a problem only during business hours, what are the site policies on escorting visitors? Are those policies followed? If visitors are not a problem, insiders who might not want to use their own computer accounts for mischief might feel free to use those of others. Physical access also makes it easy for the attacker to install such things as hardware or software keyboard sniffers.

Opportunistic Introduction of Software (Viruses)

Because personal computers were not designed to be multiuser machines, they are quite vulnerable to computer viruses. The problem is that any program running on a PC has essentially complete access to all hardware and software on the system. A virus can flash messages on your screen, alter other programs to propagate itself, or erase your hard disk. Antivirus software attempts to combat these problems by matching new software against a library of known viruses and by intercepting suspicious system calls.

Classically, viruses get into PCs by riding along with new software as it is loaded. Whenever a floppy disk is written by an infected machine, the virus adds itself to the disk. When the disk is run on another system, the virus has a new home.

Software in the original packaging is not immune. It is possible for viruses to be introduced into software during manufacturing if the master disk becomes infected before duplication. When this happens, it is a source of huge embarrassment to the vendor, but that doesn’t help the victims.

Network Security Problems

Personal computers are capable of using network file servers and are usually capable of exporting or publishing the content of the local hard disk to the network. If the security settings of such network file systems are set improperly or not set at all, the computer or the information on it may be compromised. Moreover, because client computers sometimes run network servers, such as personal Web servers, many of the security aspects of operating server computers apply also to clients.

To the extent that clients use insecure communications over their local networks, they are accessible to any machine connected to that LAN. This is particularly important with the widespread use of 802.11b wireless LAN technology. 802.11b incorporates security technology known as Wired Equivalent Privacy, but recent exploits have found the built-in security of 802.11b to be essentially worthless.

to be continued

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