The Trouble With Live Data
The cheapest, most reliable, and most secure components of any system are the ones that aren't there. Is it possible to solve the live data problem by avoiding the use of the advanced tools that pose the threat?
It probably isn't practical for a site administrator to outlaw such tools. For one thing, they are all too useful, and one has to weigh a possibly substantial security risk against a threat to an organization's competitiveness. In addition, it is unlikely that any but the most draconian site administrators could prevent users from acquiring their own personal web browsers or MIME e-mail clients. Fascist site administration might make matters worse, since the individuals who were using the outlawed tools would obviously not be informing site security staff of what they were doing.
Internet firewalls are becoming a popular security mechanism. However, it doesn't seem likely that they can protect against hostile live data. They could completely block risky services (like e-mail and the Web), but if you completely block those services there isn't much point to being on the Internet. It also does not seem practical for a firewall to inspect all data coming from the net and looking for “dangerous” activities. For one thing, we don't have a good mechanism for distinguishing “friendly” live data from “unfriendly” live data—and the most dangerous live data doesn't look live at all. Another point to think about is that the effort involved in trying to solve this problem will likely put an unacceptable performance burden on the firewall.
There does not seem to be any “silver bullet” solution to this problem. However, there are some fairly simple steps that can be taken to provide reasonable protection:
If possible, run your web browser and perform other possibly risky activities (e.g. viewing PostScript files, running programs you have downloaded) as another user ID that you use expressly for that purpose. This makes it less likely that major damage to your personal files or your system could occur.
Save your “dot files” frequently. It may also help to allow only read-only access to such files. Dot files (such as your .profile, .emacs, .exrc, or .rhosts files) are frequent targets of live-data attacks.
Probably the best advice is to be a little bit paranoid. If you get a large MIME attachment that appears to be a shell script, treat it the same way you would treat an armed bomb.
The best advice is not to avoid tools which use live data, but rather to use them very carefully. Being aware of the risks is probably the best defense. So have fun, and be careful out there.
David Bonn When he isn't busy skiing, he is usually fiddling around with Linux. When he isn't doing those two things, he is busy being president of Mazama Software Labs. Since David graduated from the University of Washington in 1986, most of his computer time has been spent working on networked systems.