Phishers Bypass Browser FiltersPhishers Bypass Browser Filters
PayPal, Bank of America, Lloyds phishing emails embedding malicious HTML files
March 18, 2011
Looks like those anti-phishing filters in your browser are working because attackers are now bypassing them by stuffing HTML files into spam messages so the malicious pages don't get detected: Researchers have detected several cases of phishers passing HTML file attachments off as Bank of America, Lloyds, TSB, and PayPal pages.
And this practice appears to be on the rise, says Satnam Narang, a threat analyst with M86 Security, which has seen an increasing number of these types of phishing messages in its spam traps. "We've seen malicious HTML attachments in spam before that directed to Canadian pharmacies. On more than one occasion, we've seen it with PayPal and Bank of America," Narang says. "But the fact is that these are becoming more common."
Unlike spam emails that try to direct users to a phishing site via a URL, this one is able to bypass the browser's anti-phishing filter and blacklist by locally storing the page. "And once the user inputs his information and sends it off to a PHP script on a legitimate website, it gets redirected to the bad guys, and they get the information," he says. "The user is none the wiser because it redirects [him] to actual sites," such as PayPal, for instance.
Narang blogged yesterday about such an attack using PayPal as the lure by requiring PayPal account verification. Here the PHP file was place on fritolay.com's website; the HTML form sends the pilfered information via a POST request to the PHP script on the hacked fritolay site.
Nitesh Dhanjani, a security expert and senior manager at Ernst & Young, says he hasn't seen local HTML files getting passed around in phishing schemes before. The technique isn't necessarily more sophisticated, but it's effective, he says.
"As always, the target market for the phishers are individuals who aren't technologically savvy. That said, given the amount of complexity involved in merely browsing the Web these days, it's becoming hard to blame the average user for not knowing how to parse URLs, domain names, and attachments to stay safe," he says. "This particular example can bypass browser sandbox models since it is loaded from the local disk. Technically impressive? No. Will it fool a large number of users and get around browser controls? Yes."
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