From: ByteRage [byterage@yahoo.com]
Sent: Friday, July 20, 2001 9:24 AM
To: bugtraq@securityfocus.com
Subject: NetWin Authentication Module 3.0b password storage
vulnerabilities / buffer overflows

NetWin Authentication Module 3.0b password storage
vulnerabilities / buffer overflows

AFFECTED SYSTEMS

NWAuth module as used by
DMail, SurgeFTP, others... (cfr www.netwinsite.com)
I've tested SurgeFTP in particular

The source code for NWAuth 2.0 can be found at
http://www.netwinsite.com/dmail/nwauth.htm
The source is provided on all platforms and for
Windows and most Unix based platforms it is
pre-compiled, as nwauth.exe or nwauth. 

DESCRIPTION

The 'NetWin Authentication module' which is used by
SurgeFTP, DMail and other programs uses a quite
'unusual' hashing algorithm to store the password
hashes. Because of the complexity of the hashing
algorithm, the users of NWAuth may not be aware of it,
but the algorithm is flawed in (at least) two ways :

1) the password hashes can be decrypted
2) one hash can match more than one password

So basically I'm saying that one user doesn't have one
password, but he can have a few million besides the
one that he was actually assigned. (no comment...)

Fortunately, SurgeFTP has some anti-hammering
techniques implemented to prevent bruteforcing.

As for the decryption, I've attached source code
(nwauthcrack.c) that will generate all possible
passwords for a given hash. The password hashes used
by fe SurgeFTP can be found within the files
\surgeftp\admin.dat (sysadmin password) &
\surgeftp\nwauth.clg (user passwords)

Storing the passwords using MD5 hashes would probably
be a better idea, maybe added up with a simple cipher
to prevent the average script kiddie from attacking
the passwordfile with canned tools. (this type of
hashing is done by Serv-U FTP)
And if one really wants to implement salting, then
append the username to the password and feed it into
the MD5 hashing algorithm, it has the same effect,
it's easier and much more secure.

=-=-

NWAuth also has alot of buffer overflows riddled
throughout the source code (especially older versions,
like 2.0), which might lead to serious flaws in
programs that use this module. Although version 2.0
probably contained much more of them, here are some
examples of buffer overflows which are still not fixed
in version 3.0b :

-> the nwauth -del command causes an access violation
when supplied with a very long username, this might
not be a big deal since only administrators are
supposed to delete users
-> the nwauth -lookup command causes an access
violation when supplied a username of about 1000
characters, this might be triggered by an attacker if
the program would pass this username from a "USER"
command

greetz,
[ByteRage] byterage@yahoo.com
[http://byterage.cjb.net]


__________________________________________________
Do You Yahoo!?
Get personalized email addresses from Yahoo! Mail
http://personal.mail.yahoo.com/