Trojan heralds OS X's 'new phase of exposure to malware'

Modular malware comes to the Mac

The Mac security scene is heating up, with the discovery in recent weeks of a serious vulnerability in OS X and at least two Trojan horse programs that target the Apple OS.

The most notable is a security hole in the latest versions of Tiger and Leopard that allows attackers to install malware on a Mac without first requiring a user to enter an administrator's password. A flaw in OS X makes it possible to circumvent the safety measure by funneling Applescript commands through the Apple Remote Desktop Agent (ARDAgent). Because the commands run as the root user, they have almost unfettered access to sensitive parts of a machine.

By the time word of the vulnerability found its way onto this Slashdot posting, malware that exploited the flaw had already been spreading on the internet for several days.

The Applescript Trojan horse template, according to this extensive post from Brian Krebs's Security Fix blog, dropped a keystroke logger onto infected Macs. It then set up a virtual network computing server, a web-based "PHP shell" program and dynamic DNS services software to make it easy for attackers to log onto the machine and manipulate it whenever it's connected to the net.

Interestingly, the exploit was was written modularly, so that the code that actually exploits the Mac weakness can be bundled with other malware code. That means the same weakness could be targeted over and over by a variety of other Trojans.

"I think that these revelations reveal that the Mac is entering a new phase of exposure to malware," Dino Dai Zovi, a security researcher who helped dissect the Trojan, told the The Register. "This shows that there is an active community of researchers who are looking for vulnerabilities in MacOS X and *not* reporting their findings to Apple."

It remains unclear how widespread the Trojan is. According to SecureMac, it has already spread to the wild through Limewire and iChat, but F-Secure and Security Fix say it was the work of hobbyist hackers who collaborated on MacShadows.com.

In addition to the ARDAgent vulnerability and the Applescript Trojan horse, Intego reported the existence of a separate Trojan. Dubbed "PokerGame," it prompts marks for their administrative password and then sends it to the attackers via email, along with sundry other data, including the machine's IP address, OS X version and hash.

The Trojan, because it requires users to be tricked, is less impressive. But it shows that malware writers continue to aspire to exploits that prey on Mac users. Stay tuned. Now that there's a template for evading OS X's password-protection mechanisms floating around, it may not be long before a newer, more sophisticated version comes to a Mac near you. ®