RE: VPN through DSL - On the subject of PPTP

["Behm, Jeffrey L." <BehmJL () bvsg com>]

Unless I misread somewhere, these are articles and/or examples about how one
*could* break in, but back to my original question...

> I have heard no one ever name an exploit

(perhaps I should have been more clear...I have seen no one name an actual
exploit _outside_ a lab environment)

I'm not into security by obscurity, either, and just because no one has
exploited it _yet_ (or at least not to my limited scope of knowledge on
exploits), doesn't mean there is not a risk, but I think the protocol is
overhyped on the exploitability (is that a word?) in real time in real
networks where people are doing real work.

Thanks for listening...My last statements on the subject.

> -----Original Message-----
> From: Patrick Darden [mailto:darden () armc org] 
> Sent: Thursday, March 14, 2002 7:57 AM
> To: Peter Lukas
> Cc: Behm, Jeffrey L.; firewall-wizards () nfr com
> Subject: RE: [fw-wiz] VPN through DSL - On the subject of PPTP
>
>
>
> In addition, unless it has changed, PPTP uses a 40 bit session key....
> Trivial to crack in real time.
>
> IPSEC allows use of 3DES at 156 bits (effectively.)
>
> --
> --Patrick Darden                Internetworking Manager             
> --                              706.475.3312    darden () armc org
> --                              Athens Regional Medical Center
>
>
> On Wed, 13 Mar 2002, Peter Lukas wrote:
>
> > On Wed, 13 Mar 2002, Behm, Jeffrey L. wrote:
> > > > I am assuming you are using ipsec instead of a severely
> > > > flawed protocol
> > > > like PPTP.
> > > I hear people say this from time to time, but I have 
> heard no one ever name
> > > an exploit that has taken advantage of the PPTP protocol 
> (other than an
> > > exploit that takes advantage *before* the data is 
> encypted, or *after* it is
> > > encrypted at the endpoints)
> > >
> > > Not that I am a Bill Gates fan, in fact, far from it, but 
> what are the
> > > severe flaws that have been exploited?
> >
> > The original Microsoft PPTP attempt left much to be desired, and the
> > second revision was fairly improved. It is by no means 
> "perfect" in the
> > peanut-gallery sense of the word, but has a number of 
> advantages going for
> > it, namely it's native to most every version of Windows and 
> as simple for
> > an end-user to set up as a dialup connection. Of course, 
> it's subject to
> > the same NAT problems as other VPN methods out there.
> >
> > The original problem was more with Microsoft's 
> interpretation of PPTP and
> > it's meager authentication scheme (MSCHAP). Dig the counterpane
> > cryptanalysis here:
> > http://www.counterpane.com/pptp.html
> >
> > The second attempt (MSCHAPv2) addressed the original 
> concerns, but is
> > still subject to similar security weaknesses as in most other plain
> > vanilla passworded VPN mechanisms out there.
> >
> > When comparing PPTP to ipsec, they both do similar things. 
> PPTP isn't
> > best used at a gateway and much better for deployment 
> across multiple
> > end-users. Using a car analogy, it's like choosing to 
> carpool with a Pinto
> > or a Volvo.
> >
> > Peter
> >
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> > firewall-wizards () nfr com
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