Home page logo
/

bugtraq logo Bugtraq mailing list archives

Windows NT rantings from the L0pht
From: owner-bugtraq () NETSPACE ORG (Aleph One)
Date: Thu, 24 Jul 1997 10:24:37 -0400


I didn't ask to be cc'd into the rantings of the MS Borg Marketing
Juggernaut but since I'm here...

I find this hillarious. The people at MS should know better.

I haven't been following this thread tremendously but I've seen
bit's and pieces. Recently there was an attrocious article in WindowsNT
magazine, where they stated it would take 5000 or so years to break the
passwords; thus put policy in place to have users change their passwords
every 2500 years. HELLO? I think these people aren't getting it.

Let's shed some light on things shall we?

1. Thank you very little MS for dropping any reference to the l0pht,
hobbit, or myself in reference to your recent LM-Hash fix. If this
is how you "correspond" with people who point out problems to you it's
no wonder that people prefer to release things to the public instead
of your "proper" channels.

2. MS agrees that the LM hash is a horrible implementation from a
security standpoint. They respond with: "well we didn't write the
protocol that was IBM".

3. When MS had the chance to do things a different way (ie Network
challenge/response obfuscation on NT boxes) they implemented it based
upon LM techniques to break up components (see #2).

4. The LM-hash fix works great if you don't have anything but NT machines
on your network. If you want to continue being "productive" with your
win95 machines it is my understanding that you "do it insecurely" or
you are S.O.L.

5. Few places are running "nothing but NT" (ie just about everyone
has 95 or WfW boxes if MS has already gotten their foot in the door).
(see #4)

6. MS can't swallow their pride enough to say "oops", even in
technical circles where they don't have to worry about the general public
mis-interpreting things.

7. For the LM hash you only have to break 7 characters, not 14!

8. MS keeps talking about the NT hash being so secure while refusing to
talk about how weak the LM hash is. Guess what, you probably won't be able
to use the "added security" of the NT hash on your network. Why keep
talking about something people can't use?

9. Even though the NT hash spec says you can have up to 128 char
passwords,
I'd really like someone to show me how they can type more than 14
characters
into UserManager before it starts Beep-Beep'ing at them.

10. We demonstrate up front with proof of concept code in L0phtcrack v1.0,
and L0phtcrack v1.5 that the following is indeed the case.

For those that don't know, L0phtcrack v1.5 will attack the challenge
response done over the network. The reason we came out with this was that
the SYSKEY "fix" that MS came out with only managed to emasculate the
ADMINISTRATOR and not address the actuall problem. Can we say "save
face"? I knew we could.

L0phtcrack v1.5 is available for FREE from http://www.L0pht.com (that's
a ZERO after the 'L', not an 'o') . It comes with source so you can build
it on just about any platform.  It is proof-of concept code and thus
could be sped up tremendously.

Now, let's rip apart why it is so trivial to go through the LM hash on the
network. And then talk about why the NT hash doesn't matter.

 --------------------------    -----------------------------
|     16byte LM hash       |  |   16byte NT hash (md4)      |
 --------------------------    -----------------------------

We already know that you only have to go through 7 characters to retrieve
passwords (up to 14 chars in length) in the LM hash, and that since there
is
no salting being done, constants show up all over the place giving away
too much information and speeding up attacks tremendously.

  -------------------------------------------------
 | 1st 8bytes of LMhash  | second 8bytes of LMhash |
  -------------------------------------------------

1st 8 bytes are derived from the first seven characters of the password
and
the second 8 bytes are derived from the 8th through 14th characters of
the password. If the password is less than 7 characters then the second
half will always be: 0xAAD3B435B51404EE.

Let's assume for this example that the users password has a LM hash of
0xC23413A8A1E7665fAAD3B435B51404EE (which I'll save everyone the
nanosecond
it would have taken for them to plug this into L0phtcrack and have it
tell them the password is "WELCOME").

Here's what happens to this hash on the network:

  --------                  --------
 |   A    | <______________|  B     |
 |        |                |        |
  --------                  --------

B sends an 8 byte challenge to A. (assume 0x0001020304050607)

Machine A takes the hash of 0xC23413A8A1E7665fAAD3B435B51404EE
and adds 5 nulls to it, thus becoming
0xC23413A8A1E7665fAAD3B435B51404EE0000000000.

The string 0xC23413A8A1E7665fAAD3B435B51404EE0000000000 is broken into
three groups of 7:

C23413A8A1E766   5fAAD3B435B514   04EE0000000000

The 7 byte strings are str_to_key'd (if you will) into 8 byte odd parity
des keys.

Now we have :

| 8byteDeskey1 |      | 8byteDeskey2 |    | 8 byteDeskey3 |

8byteDeskey1 is used to encrypt the challenge 0x0001020304050607. Let's
assume the result is 0xAAAAAAAAAAAAAAAA.

8byteDeskey2 is used to encrypt the challenge 0x0001020304050607. Let's
assume the result is 0xBBBBBBBBBBBBBBBB.

8byteDeskey3 is used to encrypt the challenge 0x0001020304050607. Let's
assume the result is 0xCCCCCCCCCCCCCCCC.

The three 8byte values are concatenated (!dumb!), and the 24 byte response
of 0xAAAAAAAABBBBBBBBCCCCCCCC is returned to the server. The server does
the same thing to the hash on it's end and compares the result to the
24 byte response. If they match, it was the correct original hash.

Why this is boneheaded:
----------------------

7 char or less passwords.

     --------------------  --------------------  --------------------
    |   C23413A8A1E766   ||  5fAAD3B435B514    ||   04EE0000000000   |
     --------------------  --------------------  --------------------

The first thing we check is to see if the users password is less than
8 characters in length. We do this by taking the 7 byte value of
0x04EE0000000000, turning it into an 8 byte odd parity DES key,
 and encrypting it against the 8 byte challenge of 0x0001020304050607.
If we get the result of 0xCCCCCCCCCCCCCCCC then we are pretty sure
it's < 8 chars in length.

In order to be sure we can run through 0x??AAD3B435B514 (ie 256 possible
combinations) to see that 5f shows us the result is 0xBBBBBBBBBBBBBBBB,
proving that the password is less than 7 characters and also giving us
the last byte of the first half of the LM hash.

From this point, even assuming we're just joyriding and not worried about
optimizing the way this is done (believe me, there are much more
effective ways to do this that reduce the amount of time needed even
further... this whole this is just showing that even a simplistic
attack works against this implementation), it's no different than
how a tool like L0phtcrack attacks the hashes in the registry.

8 char or greater passwords.

     --------------------  --------------------  --------------------
    |   C23413A8A1E766   ||  AC435F2DD90417    ||   CCD60000000000   |
     --------------------  --------------------  --------------------

The first thing to check is whether the password is less than 8 characters
in length. Deriving the 8 byte odd parity des key from 0x04EE0000000000
and encrypting against 0x0001020304050607 does not, in this case, give
us 0xCCCCCCCCCCCCCCCC, so we know that the password is 8 characters or
greater.

It takes us, in a worst case scenario, 65535 checks to figure out that
the 2bytes that are used in the last third are 0xCCD6. Even approaching
this in a completely brain-dead fashion (hey, turn-about is fair play),
you can go through your 7 digit combinations of characters for the
first third the same way you would the LM hash from the registry. This
will yield not only the first third of the response, but also the
first byte of the second third. Keep in mind that you already have the
last two bytes that made up the third third.

You could approach the middle third in the same fashion.

(note: this whole method that MS is doing screams for a precompute
table lookup attack - which given the small enough potential values
is not impossible by any means)

Thus, the challenge response is completely brute-forcable for the LM-hash.

MS made the "oversight" of still sending the LM-hash response along with
the NT response even when SP3 was installed. Thus it was a moot point
as to how tough or well done the NT hash might or might not be.

Since installing the LM-fix precludes continued use of windows 95 machines
in regards to talking to NT machines, it is still a moot point as to
how tough or well done the NT hash might or might not be.

The LM hash is incredibly weak and your more secure NT hash is brought
down to the lowest common denominator.

Thus, the challenge response is completely brute-forcable for the LM-hash.

MS made the "oversight" of still sending the LM-hash response along with
the NT response even when SP3 was installed. Thus it was a moot point
as to how tough or well done the NT hash might or might not be.

Since installing the LM-fix precludes continued use of windows 95 machines
in regards to talking to NT machines, it is still a moot point as to
how tough or well done the NT hash might or might not be.

The LM hash is incredibly weak and your more secure NT hash is brought
down to the lowest common denominator.

It would have been nice if you could type a password greater than 14chars
into the UserManager app.

.mudge

--------------------
http://www.l0pht.com/advisories.html - for more security related articles
                                       published by the L0pht
--------------------



  By Date           By Thread  

Current thread:
[ Nmap | Sec Tools | Mailing Lists | Site News | About/Contact | Advertising | Privacy ]