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[ISN] Mystery web infection grows, but cause remains elusive


By Dan Goodin in San Francisco
The Register
16 Jan 2008

The mystery over a cluster of poisoned websites distributing a toxic 
malware cocktail may be better understood but it's still not solved.

Five days ago, we wrote about the infection of several hundred websites 
[1] that was unlike anything seasoned researchers had seen before. Mary 
Landesman, a cyber gumshoe who first brought it to public attention, 
asked for help from other security pros in figuring out how the unusual 
new technique worked. And help is what many of her peers have provided.

The sites host malicious javascript that is spontaneously created and 
randomly named only after a visitor hits the home page. That's unlike 
any other mass infection most researchers have seen before. Usually, 
infected sites merely host pointers to attacker-controlled servers, 
which in turn are used to host malware with static file names.

The innovative technique is much more than an academic curiosity. 
Because the rogue code does not exist on any server until an end user 
visits it, the javascript remains invisible to site administrators. The 
randomness also prevents most antivirus programs from detecting the 
javascript. Equally frustrating, it prevents researchers from running a 
simple web search that ferrets out every web address where the attack 
code is hosted.

>From her perch at ScanSafe, a company that provides real-time 
intelligence to large businesses about malware-spreading sites, 
Landesman could see several hundred websites exhibiting the odd 
behavior. Based on intelligence from firms with sensors elsewhere on the 
net, it turns out that the number of infected sites is much bigger.

According to independent reports released earlier this week by 
SecureWorks and Finjan, 10,000 or more websites are similarly infected. 
As of Tuesday, almost all of these were still infected. They are 
churning out malware, which preys on at least nine different 
vulnerabilities in programs such as the QuickTime media player, Yahoo! 
Messenger and Windows operating systems to install a backdoor on end 
users' computers.

Alive and kicking

Attackers "want to have their malicious code live and kicking for a 
longer time so it will be much more difficult to identify that this 
website was compromised," says Yuval Ben-Itzhak, chief technology 
officer at Finjan, a security provider that's been monitoring the 
attacks since December. "The longer they will have the malicious code 
out there, the better the chances they'll infect people."

Once the malware successfully finds an unpatched vulnerability, it 
installs the Rbot Trojan, or one of its variants. Many antivirus 
programs still fail to detect the exploit.

The infection dates back at least to late November, according to this 
thread [2], which was dredged up by a Reg reader [3] in response to our 
earlier story. The online discussion shows web administrators from many 
companies reporting infections that were using multiple exploits to 
attack end users, and documents their difficulty in disinfecting the 

Landesman also reports how hard it is to remove the attack code from 
tainted web systems. Over the weekend, she noticed two modules - one 
called mod_bwlimited and the other enable_dl - in the Apache webserver 
that were responsible for transmitting the randomized malware onto end 
users' machines. But when she disabled them, she was dismayed to find 
the changes reversed and that the machines had soon resumed their 

Initially, ScanSafe and SecureWorks researchers suspected the attacks 
were the result of a web-side rootkit that creates and delivers the 
randomized files after a victim visits the site. After an earlier 
version of this story was published, however, Don Johnson of SecureWorks 
called to say he no longer believes that is the case.

Instead, he says, attackers have managed to install an Apache runtime 
patch onto the infected machines. The patch launches code into the 
Apache memory that monitor requests and transmits the randomly named 
payload into the response data. Apache modules generally have the 
ability to load or unload new modules without root access, and that 
seems to be the case here.

But so far no-one - not ScanSafe nor SecureWorks, Finjan or any other 
researcher we've contacted - knows for sure how these mostly mom-and-pop 
ecommerce sites are getting infected in the first place. The 
vulnerability is unlikely to reside in Apache, given the sheer number of 
variants that different infected machines are running.

Access all areas

Infected sites also use a wide number of different web hosts, making 
that an unlikely entry way for attackers. While Cpanel, a tool for 
remotely administering the site, appears to be modified by the 
infection, Landesman says her research suggests that is also not the way 
attackers gain access.

This is a problem, because if you don't know how thousands of of 
machines are being commandeered, you can't prevent tens of thousands 
more from suffering the same fate.

"Every time I think I have some common thread, I find some exception to 
the rule," says Don Jackson of SecureWorks. "How do we stop websites 
from experiencing this again? We really don't know what controls we need 
to put in place."

If Jackson's theory about the runtime patches proves correct, it's 
likely they were installed using compromised passwords for FTP servers 
or hosting applications connected to the infected web server. He posits 
a modified dictionary attack could have been the initial way in.

What's really needed now is for operators of websites that are infected 
to step forward and allow a trusted researcher to inspect the machine. 
(One webmaster from a site mentioned in Friday's article volunteered to 
help Landesman, but by then he had already wiped his system clean, 
removing crucial evidence in the process.)

If you've seen the behavior described above lurking on your site, please 
leave a comment below, or contact your reporter using this link [4]. 
Similarly, if you're a researcher with insight into this program please 
do the same.

With a little more digging, we'll solve this mystery.

[1] http://www.theregister.co.uk/2008/01/11/mysterious_web_infection/
[2] http://www.webhostingtalk.com/showthread.php?t=651748
[3] http://www.theregister.co.uk/2008/01/11/mysterious_web_infection/comments/
[4] http://forms.theregister.co.uk/mail_author/?story_url=/2008/01/16/mysterious_web_infection_continues/

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