Message-ID: <00c801c37609$381ec630$550ffea9@rms>
From: rms at computerbytesman.com (Richard M. Smith)
Subject: Should ISPs be blocking open ports for their customers?

This white paper was just published today by SANS:

Internet Service Providers: The Little Man's Firewall?
http://www.sans.org/rr/special/isp_blocking.pdf

A large percentage of malicious traffic is focused on a small number of
vulnerabilities and their associated ports[1]. Blocking some of these
ports will isolate infected machines and slow the spread of malicious,
autonomous code such as worms. However, the vulnerable services used by
these worms do have legitimate uses. If secured properly, they can be
used without the risk of infection. In this paper, we focus on ISPs that
provide Internet access to consumers. This paper assumes that a consumer
is a home user or a small business without dedicated IT staff. This
paper does not apply to backbone infrastructure providers or co-location
providers.

In part of this paper, we argue for blocking ports commonly used for
Microsoft File sharing and related services; specifically, ports 135,
137, 139, and 445. These ports and, in particular, Microsoft File
Sharing, draw a lot of attention from malware authors.

...

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