The Flashback malware that eventually infected more than 600,000 Macs worldwide probably started from tens of thousands of WordPress blog sites that had been hacked into and compromised, according to researchers at Kaspersky Lab.
In March, the malware creators changed the way they wanted the Flashback exploit to spread, moving it from a Trojan horse that enticed users to click on it by masquerading as an Adobe update to a drive-by attack that infected the systems of users who clicked on compromised or malicious Websites, according to Alexander Gostev, head of the global research and analysis team at Kaspersky.
In a post on Kaspersky’s SecureList blog, Gostev said that sometime around the end of February and the beginning of March, “tens of thousands of sites powered by WordPress were compromised. How this happened is unclear. The main theories are that bloggers were using a vulnerable version of WordPress or they had installed the ToolsPack plug-in.”
Websense officials in March reported that ToolsPack was a rogue WordPress plug-in that worked as a backdoor that gave the malware writers access to the system.
Estimates of compromised WordPress sites ranged from 30,000 to almost 100,000, with 85 percent located in the United States, he said.
Essentially, the compromised WordPress blogs contained code that silently redirected users who had clicked on the blog to another site, Gostev said. The malicious site determined key attributes of the users’ systems, including the operating system and browser version running on the machine. That information was sent to another server, which then sent the appropriate malware for the system’s operating environment.
For Mac users, that malware was Flashback—or what Kaspersky called FlashFake—he said.
The situation was made even more dangerous for Mac users because of Apple’s slow response to patching the vulnerability in Java that enables the attack, Gostev said. Security researchers first detected the use of exploits to distribute Flashback in February—such exploits date back to 2008 and 2011—and the vulnerability was first reported in March. Oracle had issued a patch for the exploit in February, but users whose systems ran Mac OS X were still vulnerable.
“This was because Apple never uses patches from Oracle and creates its own patches to close Java vulnerabilities,” he wrote. “The [Apple] patch for Mac OS X which closed the … vulnerability was released in early April.”
Such a two-month delay is normal for Apple, Gostev said, pointing to two other instances in 2009 and 2011 when Apple waited a month or two after Oracle issued a patch to release one of its own.
Since reaching a high of more than 600,000 infected Macs—more than 1 percent of all Macs worldwide—earlier this month, the number of infected systems has declined. Symantec officials this week said the number had fallen to 140,000, though they warned it was leveling off. Kaspersky researchers said their “sinkhole” operation—designed to reduce the spread of malware and monitor it—show just more than 30,000 infections.
Flashback was the latest in a growing string of attacks aimed at Apple systems running Mac OS X, and security experts have predicted the number of attacks will continue to rise as the popularity of these Apple systems—not only Macs, but also iPads and iPhones—grow.
“In 2011, Apple was estimated to account for over 5 pecent of worldwide desktop/laptop market share,” Kaspersky Lab expert Kurt Baumgartner said in an April 19 blog post. “This barrier was a significant one to break—Linux maintains under 2 percent market share and Google Chrome OS even less. This 15-year peak coincided with the first exploration by the aggressive FakeAV/Rogueware market targeting Apple computers … which no longer seems to be such an odd coincidence.”