Fortress Mac Is Gone

Updated: Malware breaches the Mac moat.

Several pornography sites are loading a Trojan disguised as a video codec required to view content on Macs—the first Mac-targeted malware exploit to be spotted in the wild and validation of security researchers' long-maintained prediction that, sooner or later, the rationale for Mac security smugness would rub off.

"[Users infected by visiting questionable Web sites] began using Macs as most malware target the Windows operating system. Well, soon enough, it may not matter which OS you are using," said Symantec's Joji Hamada in a Nov. 1 posting.

Sunbelt Software and Intego, a maker of Mac security software, are warning that a mother lode of spam has been posted to many Mac forums in an attempt to trick users into visiting sites with rigged porn photos. The photos are from reputed porn videos. If Mac users click on the stills to view the videos, they're taken to a site that informs them that the QuickTime Player is unable to play the movie file. They're then instructed to click to download a new codec.

Sunbelt reports that the fake codec is a variant of Trojan.DNSChanger, malware that's been plaguing Windows users for some time. Symantec Security Response has confirmed the finding and has added detection for the threat as OSX.RSPlug.A.

Intego says that after the page loads, a disk image (.dmg) file downloads to users' Macs. If users have checked "Open 'Safe' Files After Downloading' in the General preferences of their Safari browser—or similar settings in other browsers—the disk image mounts. The .dmg file contains an installer package that then launches.


Otherwise, if users wish to install the codec, they double-click the .dmg file, then double-click the package file, which is named install.pkg.

If users continue with the installation, a Trojan program installs. Installation requires an administrator's password, which grants the Trojan full root privileges. No video codec is actually installed. If users return to the purported porn site, they just receive the download anew.

The Trojan uses a sophisticated method, via the scutil command, to change the Mac's DNS server. When the new, malicious DNS server is active, it hijacks some Web requests, leading users to phishing Web sites that are after account information for sites such as eBay, PayPal and some banks, or simply to pages displaying ads for other porn sites. "In the first case, users may think they are on legitimate sites and enter a user name and password, a credit card, or an account number, which will then be hijacked. In the latter case, it seems that this is being done solely to generate ad revenue," Intego said in its release.

Running Mac OS X 10.4, the GUI has no way to display the changed DNS server. Running Mac OS X 10.5, it can be seen in the Advanced Network preferences, Intego officials said. However, Trojan-installed DNS servers are dimmed and can't be removed manually. Intego said it's now testing previous versions of Mac OS X and that they're likely vulnerable as well, given that they all have the scutil command.

The malware also installs a root crontab that checks every minute to ensure that its DNS server is still active. Since changing a network location could change the DNS server, this added touch ensures that, in such a case, the malicious DNS server remains the active server, Intego officials said.


Heise Security's Juergen Schmidt told eWEEK that this malware is related to the security company's recent findings on holes in Leopard's firewall. If a user were to install the fake video codec, it could install a backdoor on a Leopard system that can let in remote attackers, even if the Leopard firewall has been configured to block all incoming connections, if there isn't a hardware firewall in front of the Leopard system.

Schmidt noted that this Trojan also provides different versions of itself, perhaps according to the country in which the user is located to provide country-specific spoofing. "Repeated downloads of the disk image show that there are several different versions," he said.


To see an eWEEK Labs' walk-through of Leopard, click here.

Tom Ptacek, founder of Matasano Security, told eWEEK that the threat to Macs is real, although it's not a huge one—just the same old scenario Windows users face every day.

It is an interesting story, however, given that it's the first OS X malware to be "weaponized." Unlike prior OS X malware, which was all about ego, this one's out to make money, Ptacek said—again, same old, same old in the world of Windows.

Unsurprisingly, there are more than a few I-told-you-sos ensuing in security circles. "For years, we've heard snorts of derision from Mac users about the poor security of PCs. Yet that supercilious attitude (as we know from our history books) is patently dangerous, because it creates a false sense of security. Now, Mac users will need to be a bit more careful out there ('cause when Joey wants his pr0n, he wants it now!). On the heels of the poorly-secured release of Leopard, we now find that there is no perfect protection against human stupidity social engineering, even for a Mac user," said Alex Eckelberry, Sunbelt president, in an Oct. 31 posting. "Disclaimer: We have a Mac at the house among our many computers. I like Macs. I just don't care much for an attitude of high self-importance."

But as Ptacek has said before and says again, "Matasano laughs at people who buy OS X anti-virus," and this latest Trojan doesn't change that.

"There is virtually no malware targeting Leopard; if we had 100 more 'RSPlug' discoveries in 2007, the malware market share for OS X still wouldn't track the real world market share of OS X itself."

Editor's Note: This story was updated to correctly render Alex Eckelberry's note on social engineering. The author neglected to render a portion in struck-out text as Eckelberry had done in his blog and regrets the error.

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