In light of Paul Ashton's recent posts (nicely done Paul!) - someone brought to my attention that the rant and descirption that I posted to some of the lists wasn't on bugtraq. (I'd like to take this opportunity and pull a Theo Deraadt and state - this was brought up in the readme to l0phtcrack 1.5 and posted publicly on July 23 1997) -- oh yeah, OpenBSD does not appear vulnerable etc. etc. :-) Appologies if this did make it to bugtraq and I just missed that fact - the memory goes ya know. The important thing to note is that, paying attention to the network section of the below rant, it is easy enough to obtain the original hash which is used for the SMB signing that SP3+hotfixes offers - thus defeating the SMB signing mechanism (not that I see much of that in the wild anywho) .mudge --- begin old rant --- 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 from the bit's I've seen and from an attrocious article in WindowsNT magazine, where they stated it would take 5000 or so years to break the passwords so put policy in place to have users change their passwords every 2500 years, I'm believing people just 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. 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. 8. 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. It would have been nice if you could type a password greater than 14chars into the UserManager app. .mudge
This archive was generated by hypermail 2b30 : Fri Apr 13 2001 - 13:41:53 PDT