RE: Prevent security bypass

["Larry Seltzer" <larry () larryseltzer com>]

Are you thinking of the difference between Basic and Integrated authentication in IIS?
In any event, I believe the standard challenge response is MS-CHAP:

According to
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vsent7/html/vxconIISAut
hentication.asp: "Integrated Windows authentication is the best authentication scheme in
an intranet environment where users have Windows domain accounts, especially when using
Kerberos. Integrated Windows authentication, like digest authentication, does not pass
the user's password across the network. Instead, a hashed value is exchanged."

According to http://www.microsoft.com/windows2000/en/advanced/help/auth_mschap.htm:
"Microsoft created MS-CHAP to authenticate remote Windows workstations, providing the
functionality to which LAN-based users are accustomed while integrating the encryption
and hashing algorithms used on Windows networks. It uses a challenge-response mechanism
with one-way encryption on the response.

Where possible, MS-CHAP is consistent with standard CHAP. Its response packet is in a
format specifically designed for Windows NT and Windows 2000, and Windows 95 and later,
networking products. In addition, MS-CHAP does not require the use of plaintext or
reversibly encrypted passwords."

-----Original Message-----
From: Adam [mailto:a.bardsley () lancaster ac uk] 
Sent: Thursday, February 06, 2003 5:05 AM
To: Adam
Cc: webappsec () securityfocus com
Subject: RE: Prevent security bypass


I might be wrong about this but I couldn't find anything on MS' site (who
can?) but I thought the standard NT challenge response was sent unencrypted. If this has
changed I'd love to know because t would sure make my life easier :)

Adam

-----Original Message-----
From: Chris Travers [mailto:chris () travelamericas com]
Sent: 06 February 2003 07:20
To: Adam
Cc: webappsec () securityfocus com
Subject: Re: Prevent security bypass


Adam wrote:

> It depends how secure you want it as a lot of people have said but I 
> would personally go for what you suggested as bar the v.expensive 
> suggestions or the ones relying on being on the same NT network you 
> arent going to get anything very secure. We have a secuirty script 
> called on each secure page. The overhead doesnt seem that bad tbh.
What makes you say that?  If you are on NT, then any insecurities of the authentication
protocol are ALREADY going to affect you.  Applying diversity in depth might buy you
something but only if it is paired with good NT security practices,  Besides, if your
server is not secure, you are already screwed.

The way I design my web applications which require granularity of permissions for
different users or other advanced security features is based on the following
principles:

1)  Primary Security on Backend-- don't try to do any more enforcement than you have to
on the middleware.  And avoid ANY enforcement of anything important on the front-end.
Instead, try to do as much enforcement with the backend components as possible and only
suppliment with the middleware as needed.  The idea here is that you enforce permissions
using the web server, operating system, and/or information store (such as RDBMS and
LDAP) as much as possible because these are the most robust security-wise, and they can
be attacked independently anyway.  Furthermore these are the only solutions that can
globally protect the information (from inside the web context or outside it).

2)  Supplimental Security in Middleware-- Sometimes, it is necessary to place
information in the information store in an insecure fassion,and this could be used for
DoS attacks.  One example might be a user profile in an RDBMS system where all users
will be able to write to and update that table.  In this case, enforce additional
security on the middle-ware.  But this security is much more brittle and not as strong,
so it should not be relied upon as much.

3)  Protect content In Transport-- Use SSL to protect the content and passwords.

Best Wishes,
Chris