Subject: Re: PPTP AUTHENTICATION

From: James Carlson <[email-masked]>
Date: Wed, 16 Jun 1999 15:47:52 -0400 (EDT)

> So there is *no* standard protocol that supports change password. 

Not for PPP, no.

> Thanks for clarifying that you made a mistake in your somewhat loose
> comment.
> 
> Gurdeep
> =======
> 
> PS: your plausible attempt to show change password as a "bug" is sure to
> impress some folks. I stopped reading after the small leap "first I steal a
> copy of MD4 hashed registry...." 

I figured as well.  Of course, the registry is perfectly secure and
cannot be compromised.

http://www.martnet.com/~johnny/exploits/microsoft/NT/WinNT.passwordhashes.deobfuscation.html
http://www.kull.ch/Bauersachs/cracknt_e.asp

-- 
James Carlson, Software Architect                   <[email-masked]>
IronBridge Networks / 55 Hayden Avenue   71.246W   Vox:  +1 781 372 8132
Lexington MA  02421-7996 / USA           42.423N   Fax:  +1 781 372 8090
"PPP Design and Debugging" --- http://people.ne.mediaone.net/carlson/ppp

---

From: Gurdeep Singh Pall <[email-masked]>
Date: Wed, 16 Jun 1999 12:33:51 -0700

Gurdeep
=======

-----Original Message-----
From: James Carlson [mailto:[email-masked]]
Sent: Wednesday, June 16, 1999 12:20 PM
To: Gurdeep Singh Pall
Cc: [email-masked]
Subject: Re: PPTP AUTHENTICATION

> James, how do you do change password (a feature in ms-chap-v-anything)
with
> a "standard" protocol?

You do it via a separate mechanism; any that is validated by the
administrator of the authenticating system will do.  Some security
folks may want physical identifiers to do this; some may do it with a
script.

I view the ability to set the password as a bug, not a feature, in
MS-CHAP.  The bug here is that I can use this security hole to break
into an NT system.  To break in, I first steal a copy of the MD4-
hashed registry.  Then, I use this with a modified implementation of
MS-CHAP (note that the Unix version of this is available as free
source code) that doesn't bother doing the meaningless MD4-hash step
-- it just authenticates using the stolen hash value.  Next, I use
MS-CHAP to change the compromised user's *actual* password.  Now I can
both connect to the network and authenticate as that user for access
to systems on the network as well, since NT is reusing this
authentication mechanism to validate user access.

If this hole weren't designed into MS-CHAP, as it isn't in standards-
compliant CHAP, then stealing the registry wouldn't help much.  I
would be able to connect to the network and pass packets, but I
wouldn't have access to any of the nodes on the network, since they
would each want to challenge me for my knowledge of the true password
(which I don't have), or, if the administrator had any smarts at all,
for a *different* password.