As part of their security packages, these browsers receive URLs of known phishing sites and won't go to them unless users specifically permit them to. But a technique discovered by M86 Security Labs gets around this 'blacklist' protection.
The new ploy doesn't require victims to visit phoney websites to fill out forms that appear legitimate and reveal passwords, account numbers and the like. Instead, spammers send the forms as HTML attachments to emails. When victims fill out the forms and click to submit them, the data is sent through the browser via a POST request to PHP web servers that have been hacked.
"While the POST request sends information to the phisher's remote web server, Google Chrome and Mozilla Firefox did not detect any malicious activity," the blog says. "Months-old phishing campaigns remain undetected, so it seems this tactic is quite effective."
The browsers don't pick up on this activity as malicious, partly because not many compromised PHP servers get reported so their URLs don't make the blacklists. Most users aren't sophisticated enough to discern the URL from the PHP submission, M86 says in a blog.
Also, because the PHP script doesn't show any HTML code to the browser, the URLs that the data is sent to are hard to verify as phishing sites, the blog says.
In a specific case that M86 describes, the PHP server involved had been installed on a compromised Frito-Lay web page. After grabbing the victim's data, the PHP script redirects the browser to the legitimate company the victim thought it was dealing with.