risk level associated with VPNs?

[Avishai Wool <avishai_w () yahoo com>]

Dear all,

While doing firewall policy analyses for customers,
I very often come across rules that allow 
  any ip traffic
  from anywhere outside the primeter 
  into big portions of the inside networks
but over a VPN link (i.e., encrypted & authenticated).

let's put aside the question of whether the authentication is
sufficient, and assume that nobody is cracking the passwords.
I tend to trust the encryption and believe that noone can snoop
the traffic in flight.

My claim is that these rules are very risky and a wonderful 
vector for all kinds of malware. All those home 
computers, laptops on the road etc, are much more at risk 
of infection than inside computers are. Plus the VPN has the
nice side-effect that filters can't see though the encryption
and control (or even log) where the connection is going
and what it is doing.

Left to my own devices, I would recommend terminating the VPNs 
in a DMZ, and putting all the usual controls (anti-virus/mail filter/etc)
between the DMZ and the inside, and I would flag these raw VPN connections
as risky, maybe even very risky.

However, customers uniformly disagree with this argument, and tell me that 
"traffic coming over a VPN is not perceived as a risk so shut up
about it."

Thoughts anyone?
Any credible war stories about malware/abuse traveling over VPNs?
Or are the customers right and I'm being paranoid? 
 (please don't respond that "the customer is always right" :-)

Thanks,
  Avishai

=====
Avishai Wool, Ph.D.,                    
http://www.algosec.com               http://www.eng.tau.ac.il/~yash
yash () acm org     Tel: +972-3-640-6316  Fax: +972-3-640-7095

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