Monday, December 28, 2009

Cracking Mac OS X Passwords

In this post I will demonstrate how to both extract and crack Mac OS X passwords. The OS X variants that this tutorial is aimed at are 10.4 (Tiger), 10.5 (Leopard) and 10.6 (Snow Leopard).

Whilst Mac OS X is based on a Unix variant (BSD), there are several key differences between traditional Unix-based and Mac OS systems when it comes to password storage. Lets take a quick look at some of the differences.

If you have ever poked around on an OS X system, you may have noticed the absence of the /etc/shadow file. Whilst traditional Unix and BSD variants store their password hashes in /etc/shadow and /etc/master.passwd respectively, Mac OS X does not. Since the release of OS X 10.3 in 2003, Macintosh products have stored their shadow files in the /var/db/shadow/hash/ directory.

Another key difference is the way in which the two systems store their hashes. On a Unix-based system, every hash associated with the system is stored in the /etc/shadow file. This differs from OS X whereby each user has their own individual shadow file stored in the /var/db/shadow/hash/ directory. Each file is labeled by the user’s Globally Unique Identifier (GUID). N.B. A GUID is analogous to a Security Identifier (SID) on Windows-based systems.

Lastly, most Unix variants will use multiple rounds of the MD5 or DES cryptographic hash functions in order to encrypt system passwords. OS X systems encrypt passwords with the SHA1 hash function, coupled with a 4 byte salt.

In sum, OS X password storage has the following characteristics:

  • Password hashes are stored in the /var/db/shadow/hash/<GUID> file
  • Each user has their own shadow file
  • Local OS X passwords are stored as SHA1 hashes

STEP 1. OBTAINING THE GUID

So, the first thing we want to do in this exercise is find out what our GUID is. We do this by invoking the Directory Service command line (dscl) utility. Implemented in OS X 10.5 to replace the deprecated NetInfo directory service, dscl uses the Open Directory Framework to store, organise and access directory information. For our purposes, the directory service holds information specific to each user on the system.

The command we use to extract our GUID is as follows:

Note: Replace <username> with the username of the user you wish to extract.

10.4 (Tiger)

# niutil -readprop . /users/<username> generateduid

10.5 (Leapord) and 10.6 (Snow Leapord)

# dscl localhost -read /Search/Users/<username> | grep GeneratedUID | cut -c15-

This should return a value which appears in the following format: A66BCB30-2413-422A-A574-DE03108F8AF2

STEP 2. EXTRACTING THE HASHES

Next, we want to extract the SHA1 hash from the shadow file. For this, we do the following:

# cat /var/db/shadow/hash/A66BCB30-2413-422A-A574-DE03108F8AF2 | cut -c169-216

Note: Replace the above GUID with the one you have extracted from the previous step.

You should have been returned with a SHA1 hash that looks similar to the following: 33BA7C74C318F5D3EF40EB25E1C42F312ACF905E20540226

At this point it should be noted that OS X has the ability to store Window NT and LANMAN hash representations. This will only occur if SMB/CIFS file sharing has been turned on. To extract these passwords from the shadow file, type the following:

NT:

cat /var/db/shadow/hash/A66BCB30-2413-422A-A574-DE03108F8AF2 |cut -c1-32

LANMAN:

cat /var/db/shadow/hash/A66BCB30-2413-422A-A574-DE03108F8AF2 |cut -c33-64

STEP 3. CRACKING THE PASSWORD

At this point we are ready to crack the OS X passwords. To simplify this step, I have written a simple python script that can be downloaded here. To use this script, simply copy and paste the contents into a file (osx_crack.py) and type:

#python osx_crack.py bob

Note: 'bob' is the username whose password we want to crack.

This method is nice if you are only interesting in cracking passwords from a local system. If, however, you have captured a hash from a remote system, or would prefer a more familiar password cracking utility, then John The Ripper can also be used for this step. In order for John to work, John will need to be patched with the 'Jumbo Patch' - allowing SHA1 passwords (referred to as XSHA in John) to be cracked. The patch can be downloaded from the following locations:

Once we have download/patched John, the extracted hash and username should be placed in a text file. For this example I have added the username ‘bob’ and bob’s hash (that I obtained in STEP 2) into a file called sha1.txt. The file has the following format:

bob:33BA7C74C318F5D3EF40EB25E1C42F312ACF905E20540226

We can then use John the crack the password:

# ./john sha1.txt

If John is successful in recognising the hash, the following message will be displayed:
”Loaded 1 password hash (Mac OS X 10.4+ salted SHA1 [32/64])”

A successful cracking attempt will appear as follows:

password (bob)
guesses: 1 time: 0:00:00:00 100% (2) c/s: 153000 trying: password

Additional Resources