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Meet Stumbler: Next Gen port scanning malware

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Security experts are tracking the spread of a mysterious piece of malware which has been linked to an upsurge in distributed port scanning on the Internet.

Little is known about the malware - dubbed 55808 because of its Windows size, or Stumbler - other than that it appears to be a client capable of scanning and receiving network mapping data from other similar clients distributed across the Internet. The code is filed with errors which make it incapable of propagating automatically, according to ISS. However the security tools firm warns that further development of Stumbler to lead to the creation of potent denial of service attacks tools.

Network mapping and port scanning have been around for Donkey's years, but Stumbler has a variety of techniques up its sleeves designed to throw security researchers off its tracks. Lucky then, that only a few machines have been infected.

Stumbler uses stealth techniques in mapping hosts and services by sending a storm of spoofed probes amid one legitimate probe so that its real activity is almost drowned out by noise.

These techniques have been employed by Stumbler in conjunction with a distributed architecture, as explained here.

Each agent attempts to map IP addresses and open ports corresponding to each IP address by sending a TCP SYN packet with a random destination port. The source IP address for each packet is spoofed, and therefore the agent will not receive the response packet that would indicate if that IP address is reachable, and if the port is open. The source MAC address is also spoofed, making the source of packets harder to locate. The agent contains a promiscuous mode packet sniffer to harvest responses. The network is designed so that each agent listens for the spoofed responses from all the other agent peers. The network mapping information is collected and then sent back to a specific IP address. Stumbler makes use of the commonly used network libraries "Libpcap" and "Libnet".

Thankfully, Stumbler's code is strewn with errors and unable to propagate automatically. This greatly reduces the immediate risk it poses, as ISS explains.

This scanning network appears to be highly experimental, and certain portions of the code appear to be undeveloped or contain fatal errors. The network currently has no capability to propagate automatically, and it does not attempt to scan for and infect other hosts. Its scanning capabilities are only used for information gathering purposes.

ISS warns: "if the size of the Stumbler network was increased, it could be used as an effective platform for network mapping, Denial of Service attacks, and command-and-control of bots and other types of distributed malware".

Already copycat Trojans similar to Stumbler have been produced. One of these has been captured and analysed by security outfit IntruSec here. ®

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