New Windows Worm Wriggling Through Networks

A retro worm attack is underway that takes the unusual spin of employing the Remote Desktop Protocol (RDP) in Windows' remote desktop connection feature as its attack vector.

Researchers from Microsoft, F-Secure, eEye Digital Security, and other organizations say the so-called Morto worm infects Windows workstations and Windows servers. It spreads by uploading a Windows DLL file to a targeted machine. The worm looks for weak administrator passwords in Remote Desktop on an organization's network -- everything from "12345" to "admin" and "password."

Researchers say the attack could be used for various purposes, including distributed denial-of-service (DDoS) attacks against targeted organizations. "The remote control feature allows bot-like control of the infected machines and they can be used for basically any purpose," says Mikko Hypponen, chief research officer of F-Secure Lab.

Microsoft's Malware Protection Center (MMPC), which sounded the alarm about the worm over the weekend, on Friday added detection for Worm:Win32/Morto.A. The relative number of infections isn't as high as with other malware families, but the worm generates "noticeable" amounts of traffic, according to Microsoft.

As of Saturday, there were only a few thousand computers infected with Morto, according to Microsoft's data. That's in contrast to nearly 30,000 infected with the Sality family of malware, and more than 10,000 with IRCbot malware, according to Microsoft.

"Based on telemetry through the remainder of Sunday, August 28, we are continuing to see low detections in comparison to established malware families as mentioned in the MMPC blog," says Pete Voss, senior response communication manager for Microsoft Trustworthy Computing. "It’s important to remember that this malware does not exploit a vulnerability in Remote Desktop Protocol, but instead relies on weak passwords ... We encourage people to use strong passwords to help protect their systems."

Researchers for the Contagio blog note that Morto generates significant traffic, and appears to have ties to China and Hong Kong. "I can add that it runs what it looks like a quick DoS test against one Google IP. In addition, it creates a lot of traffic: RDP scans, downloads, receiving commands, and interesting DNS queries for command and control servers," says a post by "Mila" today. "Judging by the domain owners of CC servers (China) and their location (Hong Kong), I would say it is likely it be cybercrimeware originating in erm...Asia. I don't know how difficult it is for a foreigner to register domains with Jiangsu Bangning Science & technology Co. Ltd.in China. One of the domains existed for a few years and changed several Chinese registrars and hosting companies. Like in Russia, DDoS attack crimes are very common in China."

Once Morto compromises one system, it connects to a command and control server to download information and to update its malware. "It also terminates processes for locally running security applications in order to ensure its activity continues uninterrupted. Affected users should note that a reboot may be required in order to complete the cleaning process," Hil Gradascevic of MMPC Melbourne blogged yesterday.

Marc Maiffret, CTO of eEye, says there are some common-sense ways to prevent being hit by "this silly worm."

Among his recommendations: RDP access from the Internet should use VPN authentication. "You need to always be minimizing your attack surface, and a great example of that is not allowing RDP to be probed by any joe hacker with a port scanner," Maiffret blogged today. Stop using weak passwords, he says, and try to throw off the worm and other attacks by moving your network services to different, non-standard ports. "This can be done for RDP through a simple registry key change which makes it easy to standardize across your entire network if you so choose," he says.

Meanwhile, Microsoft says Morto also tries to connect to targeted host systems if it can't get to an admin account, using easy-to-guess usernames like "admin" and "guest," for example.

Morto is also known as Trojan horse Generic24.OJQ (AVG); Trojan.DownLoader4.48720 (Dr.Web) ; Win-Trojan/Helpagent.7184 (AhnLab); Troj/Agent-TEE (Sophos); and Backdoor:Win32/Morto.A (Microsoft).

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