A malicious addition to a Facebook link

In the last few days we have discovered that spam messages with malicious links are being sent via instant messenger services. It turns out that the mailings were carried out by the Zeroll IM worm. A bot generated various messages depending on the language of the recipient. Here are a few of them:

“Wie findest du das Foto?”
“seen this?? 😀 %s”
“This is the funniest photo ever!”
“bekijk deze foto :D”
“uita-te la aceasta fotografie :D”

Like lots of other similar incidents, the cybercriminals have made use of social engineering, asking users to look at pictures with alluring names. At the end of the message there is a link such as http://www.facebook.com/l.php?u=********.org/Jenny.jpg. As well as the link to the Jenny.jpg file the messages included similar links to Sexy.jpg.

The page that the http://www.facebook.com/l.php?u= link leads to is not actually malicious – it contains a warning from Facebook telling the user they are leaving the site.

Facebook warning

If you add a link to any random site after ‘l.php?u=’, then a window opens with a warning from Facebook. However, after the user clicks the ‘Continue’ button the link will direct the user to the corresponding site. This mechanism was used by the cybercriminals to make the link to the malicious site look more legitimate.

When the browser redirects to the page ********.org/Jenny.jpg it leads to the file PIC1274214241-JPG-www.facebook.com.exe which is then launched by unsuspecting users. Hereafter, the terms jenny.jpg and sexy.jpg refer to this executable file.

After analyzing jenny.jpg and sexy.jpg it turned out that they were typical downloaders, protected by packers and written in Visual Basic.

Fragment of the downloader code after the jenny.jpg file is unpacked in full

The downloaders’ job is typical for these types of program – download another malicious program to the infected computer. In this case, it’s the file srce.exe. So that the user doesn’t suspect anything, the downloaders also open the picture that was promised in the original spam message. The picture is downloaded from the Internet (the link can be seen in the screenshot).

So what is srce.exe? It’s a dropper + downloader whose outer shell is also written in Visual Basic. It downloads IM-Worm.Win32.XorBot.a which uses Yahoo Messenger to send out messages to users.

So what we have here is a link to a page on Facebook being used in instant messaging spam instead of a direct link to a malicious object. You could say that Facebook is being used a service along the lines of bit.ly: it allows links to be modified so that they are directed via the Facebook domain.

Zeroll is still actively sending out spam. The messages contain links to different files, but with similar names such as Girls.jpg and Marisella.jpg. And even though people already know they shouldn’t just click any old links, even if it was sent by someone on their contact list, it’s worth reminding everyone again. If nothing else, cybercriminals are creative, and the Zeroll spam once again confirms this.