A nasty new development — spammers are now exploiting closed relays to send spam, by brute-force attacking their SMTP AUTH interfaces. SMTP AUTH is a system used to allow legitimate mail server users to send outgoing mail securely, by authenticating them first. ( sample documentation here.)
This ROKSO file indicates one spammer’s modus operandi:
These relays were abused using SMTP AUTH. That is, the spammer supplied a valid username/password pair to the server, was authenticated, and therefore granted permission to send mail anywhere. Such attacks are therefore successful only when weak passwords are used. This spamhaus constantly scans the net to find abusable servers to use in subsequent spam runs. All brands of servers (sendmail, exchange, mdaemon, rockcliffe, etc) are equally targeted, as long as they support SMTP AUTH. The attacker tries several username/password pairs – such as with ‘admin/admin’ – following a certain pattern and hoping to find a combination that lets him in.
An analysis done in july 2003 has shown that a total of 276 combinations are attempted (of course new ones can have been added in the meanwhile): Usernames: webmaster, admin, root, test, master, web, www, administrator, backup, server, data, abc each with the following passwords: username, username12, username123, 1, 111, 123, 1234, 12345, 123456, 1234567, 12345678, 654321, 54321, 00000000, 88888888, admin, root, pass, passwd, password, super, [email protected]#$%^&* as well as with a blank password.
MDaemon users beware! The account creation tool of recent versions of MDaemon defaults the password to the account name. If the default is accepted, the account will be open to be exploited by this spamhaus.
Incredible. There’s no way at the SMTP/IP level to tell that this relay was compromised; blacklisting will definitely cause collateral damage in response; so content analysis is pretty much necessary, as far as I can see.
And in another worrying development: it turns out that the latest Outlook worm, W32.Swen, doesn’t bother trying to randomly generate usernames etc. or send via SMTP directly. Instead, it asks the user for their username, password and SMTP server!