Warp Trojan from China said to fool routers into spreading Windows malware

A security firm says it has spotted malware from China dubbed the Warp Trojan that takes a totally new approach: After infecting a vulnerable Windows computer, it pretends to be a router and tells the real local subnet router to send traffic for other networked computers to the infected machine, so the malware can then try to compromise the other computers through a man-in-the-middle attack.

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"It has a direct impact on all the computers on the subnet because it will intercept traffic and make changes to the traffic," says John Morris, principal security researcher at Kindsight Security Labs. The firm believes Warp Trojan hails from China and may be used as some kind of adware to drive traffic to websites there.

In some respects, Warp Trojan is pretty run-of-the-mill malware in that it infects vulnerable Windows-based computers through known Adobe and Java exploits. But it's the way the Trojan attempts to spread that sets it apart. It uses a novel man-in-the-middle attack that involves sending an unsolicited ARP request to the local subnet router in order to fool it into directing traffic to the original infected machine.

"It uses ARP, the Address Resolution Protocol, and it's telling the genuine router on the network that it, the trojanized computer, is all the other computers on the network," explains Morris. As to whether it's easy to trick routers into taking these fraudulent ARP requests, Morris says the testing done at the lab suggests that "a lot of routers don't reject an unsolicited ARP." That includes Cisco routers, according to Kindsight, which says Warp Trojan uses an older hacking tool called ZXarps to help carry out this part of the attack.

The result is that when end users on a Windows computer network start to launch their browsers to request websites, they'll be sent there -- but they'll get an extra iFrame HTML tag that will drive them to an infected website behind the scenes, according to Kindsight. These websites in China will attempt to push the Warp Trojan onto the computer, and if it's vulnerable, the Trojan will infect it and the cycle with begin again.

Morris says the Warp Trojan seems to be mainly intended for adware use in China and is not something that's becoming a major problem in the U.S. In addition, the larger context suggests the Warp Trojan doesn't appear to be a botnet used for stealing financial resources or intellectual property, for instance. But the Warp Trojan could potentially be used to drop additional malware onto infected computers, says Morris. Its novel man-in-the-middle attack is something that makes it interesting because it raises the question of whether other fraudsters could use this approach for yet more evil purposes. "It's inserting itself almost like a mock router into the network," says Morris.

Ellen Messmer is senior editor at Network World, an IDG publication and website, where she covers news and technology trends related to information security.

Read more about wide area network in Network World's Wide Area Network section.

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