Comcast using IPS to protect the Internet from their home user clients?

[Frank Knobbe <frank () knobbe us>]

This post should probably have gone to SF-PenTests, but since it is more
of a discussion item, I thought about Full Disclosure, the list for vuln
info and everything else :)


Anyhow, I noticed that certain vulnerability scans, for example scans
using Nikto and similar tools, when run from a Comcast address show a
different behavior than when they are run from a clear, uncontrolled
Internet connection (i.e. corporate T-3). In fact, it appears like
Comcast has an Inline-IDS (some call it an IPS ;) sitting on its wires,
filtering out certain signatures and blocking subsequent access for a
short period of time. For example, scan progresses, then hangs
inexplicably, then resumes, trips a sig, and hangs again. At the same
time, the same scan from a non-Comcast address continues without any
hick-ups. Targets have been ruled out (up and running, verified at the
same time from different addresses), and connectivity to the rest of the
net remains. It's looks like just the src-dst address pair is used so
that all connections from a Comcast src to that particular dst are
blocked for a short moment (1-5 minutes).

Has anyone else noticed that? Is Comcast actually attempting to keep all
those worms'n'viruses of their clients away from the Internet?

How many other ISP's are known to use IPS's inline to protect themselves
from the 'Net, or protect the 'Net from themselves?

Regards,
Frank (routing all scans via VPN through corporate hosts ;)

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