RE: Prevent security bypass

Windows Integrated Authentication in IIS/IE is a negotiation between Kerberos and NTLM (v2). Whenever possible, basically Win2k+ environments, Kerberos will always be negotiated.

NTLM v2 is a reasonably strong authentication protocol and certainly does not use "unencrypted hashes" - whatever that means. The NTLMv2 protocol has existed in its current form since NT SP4 and Win9x with the DS client pack.

If you are worried about brute-forcing the NTLM challenge response then this attack can be mitigated by turning on strong password policy and/or protecting all traffic with the web server via SSL. Brute forcing NTLM auth with strong passwords is extremely difficult and beyond the ability of all except the most determined attacker with significant resources.

MS-CHAP is not used by any Microsoft products other then IAS for RADIUS.

Adam, your life should be very easy.

Dave

-----Original Message-----
From: Larry Seltzer [mailto:larry@larryseltzer.com] Sent: Thursday, February 06, 2003 3:49 AM To: 'Adam'
Cc: webappsec@securityfocus.com
Subject: RE: Prevent security bypass

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:

Do you need help?

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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:

Do you need more help?

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>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 Received on Fri Feb 7 20:24:06 2003