Rate Limiting as an Anti-Spam Tool - ' Strong Passwords ' (
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Its the future of mail worms, and in fact the only future for mail worms. Theyre going to have to authenticate someday, so they will either need to use open relays or scam the user out of their own SMTP AUTH credentials. SMTP AUTH is the authentication scheme for end-user SMTP server access. Most ISPs require that you provide a username and password to send as well as to retrieve mail, and eventually all of them will.
Ive read stories about worms attempting to send mail on authenticated SMTP servers by guessing weak passwords. Simply by scraping e-mail addresses, you can guess the usernames (foo is the username for foo@comcast.net).
If the system doesnt force you to choose a strong password, many users will try "foo" or "password" or "asdf" or "comcast" or something else really easy. Weak SMTP AUTH credentials are an understudied problem and will come to the forefront in the next year or two for this reason.
I checked with a couple of network security scanners, and neither of them look for weak SMTP AUTH credentials. With an open scanner such as Nessus, it should be possible to write a plug-in that does the test.
For insights on security coverage around the Web, check out eWEEK.com Security Center Editor Larry Seltzers Weblog.
Rate limiting isnt a new idea for stopping spam. Microsofts famous Penny Black project, which attempts to make the sender pay for sending an e-mail by solving a computational problem that takes a fixed amount of time, is a roundabout way of implementing rate limiting.
Why not just rate limit? The Penny Black argument would be—I guess—that a recipient can rate limit the sender rather than relying on infrastructure-based rate limiting. Personally, I think theres a much better chance of major changes happening on the server end than on the client end.
Time to wake up and smell the limits. Consumer broadband accounts that provide happy hunting grounds for zombie programs will need to be restricted in their freedom to e-mail willy-nilly. Its too bad, but its not going to affect the overwhelming majority of users who have no need to send mail other than through their ISPs mail servers, and no need to send even 100 messages a day, let alone thousands.
Security Center Editor Larry Seltzer has worked in and written about the computer industry since 1983.
Check out eWEEK.coms Security Center at http://security.eweek.com for the latest security news, reviews and analysis.
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