SurfControl, a Scotts Valley, Calif.-based Internet security vendor, said that it's seen one instance of such an attack, and expects more.
"This can fool the average user for sure," said Susan Larson, SurfControl's vice president of its global threat analysis and research group.
The new phish blends traditional elements with the new twist of a self-signed digital certificate, said Larson. It starts the same as most phishing attacks, with spammed e-mails urging recipients to click on a link to update a financial account. The destination is a spoofed version of a real site which requests the consumer enter his or her username and password to verify the information (supposedly because unauthorized access has been detected from an overseas IP address).
But this campaign goes above and beyond the typical. The spoofed site uses the HTTPS protocol so that the browser shows the standard "lock" icon designating a secure site. Additionally, the site serves up a self-signed SSL digital certificate (self-signed, meaning the subject of the certificate is also the signer). That's where the trouble really starts, said Larson.
"In self-signing, you become your own certificate [issuing] authority," noted Larson. "Many enterprises have their own self-signed certificates that they use to secure documents within the company. But the very scary thing here is that most people don't know that self-signed certificates exist."
When a browser encounters a signed, secure site, it checks the validity of the certificate, and puts up a dialog box under certain circumstances, including when it sees a self-signed certificate. But those warnings aren't always understood or taken seriously by users.
"When alerts like this come up, people often click 'Yes' to continue because they've seen such warnings before and believe everything is okay," Larson said. "Some people will actually examine the certificate, and see that it's self-signed. That will tip them off that it may be a phishing attack."
But most won't go to the trouble.
"The phishers want people to be as unsuspecting as possible," said Larson. By posing as a legitimate site that's secure -- down to a digital certificate -- they're doing just that.
While the site using this technique was gone within a day -- not uncommon when it comes to phishing sites, which expire quickly as the criminals behind them move on to avoid law enforcement -- Larson expects to see others use the tactic.
"This will really step up the threat from phishers," she said.
Fraudsters could apply other techniques to mask their machinations even more. Several bogus sites in the wake of Hurricane Katrina, for instance, acted as intermediaries between consumers and the real deal, such as the Red Cross, and after snatching credit card information, passed the user along to the legitimate site, even populating the online form there so it appeared seamless.
"Phishers can act as criminal intermediaries without being detected," Larson said.
Because most people believe that a secured site -- noted by a lock icon and with a digital certificate -- is safe, Web users will have to retrain themselves, she added.
"Look at certificates," she advised. Other recommendations: set browser security settings to high, always navigate to a site by typing its address in the URL bar, and never click through any kind of link in an e-mail message.
"Enterprises should warn employee about the new scam," Larson concluded. "IT may be able to modify group policies, but that has to go with education.
"Education, education, education, that's the key."