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"Stumbler" Distributed Stealth Scanning Network

Internet Security Systems Security Alert

June 19, 2003

"Stumbler" Distributed Stealth Scanning Network


X-Force has been tracking reports of suspicious and widespread Internet

traffic with a TCP Window size of 55808. A substantial amount of traffic

captured from sites around the world point to a new distributed port

scanning system. X-Force has analyzed malware that appears to be a client

capable of scanning and receiving network mapping data from other similar

clients distributed across the Internet. X-Force has named this malware,


ANYONE KNOW OF AN IDS SIG or CUSTOM sig for this?? Thank you

  • Other Security Subjects

Re: "Stumbler" Distributed Stealth Scanning Network

Cisco IDS does not currently have the ability to identify packets with a specific TCP Window Size of 55808. However, based on the research presented, it is possible to create a custom signature / filter combination to catch the current Stumbler implementations.

1) Create a custom ATOMIC.TCP signature with the following parameters.

DstPort 22

Mask SYN | FIN | URG | PSH | ACK | RST

TcpFlags SYN

2) Create a filter for the custom alarm you created to catch for the destination

IP address "". Please consult the Cisco IDS documentation for directions on adding a signature filture.

We are looking into adding an enhancement to Cisco IDS to allow for specific TCP Window Sizes to be identified.