Cybercriminals have laced about 2,000 legitimate websites with a potent malware cocktail that surreptitiously attacks people who browse to them, a security researcher warned Friday.
Unlike past outbreaks of the mass web attack known as Gumblar, this round actually plants exploit code on the website servers themselves. Curiously, the directory and file name of the malicious payload is in most cases unique and identical to a legitimate file that existed on the website.
The trick makes it extremely difficult for webmasters and anti-malware programs to detect the threats.
"This is an ugly can of worms," said Mary Landesman, the ScanSafe security researcher who warned of the mass attack. "Any time you see a new technique evolve like this the concern is we'll be seeing much more of this in the future, and certainly it complicates the remediation of the compromised website."
Previously, Gumblar planted links in thousands of compromised websites that silently redirected users to a handful of servers that hosted the exploits. That method allowed white hats to foil the attack by shutting down one or two domains. With the malware embedded directly in the compromised websites, the take-down process is significantly more time consuming.
Also making matters hard for Landesman to get the sites cleaned up: Most of the websites belong to small businesses that cater to non-English speakers. Few of them have dedicated security employees, and even when representatives can be located, the person contacting them must speak multiple languages.
While the websites are relatively small, Gumblar architects have planted links in online discussion forums across the web that often cause RSS readers to automatically send users to the booby-trapped pages. Landesman suspects black-hat search engine optimization may also be causing the infected sites to be featured prominently in results returned by Google and others.
People who are unfortunate enough to visit the sites won't see anything unusual. But behind the scenes, a PHP script checks their version of Adobe Reader and Adobe Flash, and if either is out of date, hijacks their PCs using known vulnerabilities. If both of those programs are up to date, the script tests to see if the system is vulnerable to several bugs Microsoft has patched in the last few months.
Hijacked machines will be installed with a backdoor that gives the hijackers complete control. They are also equipped with malware that manipulates search results returned by Google.
It's unclear exactly how the sites are getting compromised. Landesman suspects FTP passwords for the sites have been lifted from administrators' computers using key-logging malware. ®