It’s an easy attack. Register a domain that’s like your target except for a typo. So it would be countrpane.com instead of counterpane.com, or mailcounterpane.com instead of mail.counterpane.com. Then, when someone mistypes an e-mail address to someone at that company and you receive it, just forward it on as if nothing happened.
These are called “doppelganger domains.”
To test the vulnerability, the researchers set up 30 doppelganger accounts for various firms and found that the accounts attracted 120,000 e-mails in the six-month testing period.
The e-mails they collected included one that listed the full configuration details for the external Cisco routers of a large IT consulting firm, along with passwords for accessing the devices. Another e-mail going to a company outside the U.S. that manages motorway toll systems provided information for obtaining full VPN access into the system that supports the road tollways. The e-mail included information about the VPN software, usernames, and passwords.
They’re already being used to spy on companies:
Some of the companies whose doppelganger domains have already been taken by entities in China included Cisco, Dell, HP, IBM, Intel, Yahoo and Manpower. For example, someone whose registration data suggests he’s in China registered kscisco.com, a doppelganger for ks.cisco.com. Another user who appeared to be in China registered nayahoo.com a variant of the legitimate na.yahoo.com (a subdomain for Yahoo in Namibia).
Kim said that out of the 30 doppelganger domains they set up, only one company noticed when they registered the domain and came after them threatening a lawsuit unless they released ownership of it, which they did.
He also said that out of the 120,000 e-mails that people had mistakenly sent to their doppelganger domains, only two senders indicated they were aware of the mistake. One of the senders sent a follow-up e-mail with a question mark in it, perhaps to see if it would bounce back. The other user sent out an e-mail query to the same address with a question asking where the e-mail had landed.
Defenses are few:
Companies can mitigate the issue by buying up any doppelganger domains that are still available for their company. But in the case of domains that may already have been purchased by outsiders, Kim recommends that companies configure their networks to block DNS and internal e-mails sent by employees that might get incorrectly addressed to the doppelganger domains. This won’t prevent someone from intercepting e-mail that outsiders send to the doppelganger domains, but at least it will cut down on the amount of e-mail the intruders might grab.
I suppose you can buy up the most common typos, but there will always be ones you didn’t think about—especially if you use a lot of subdomains.