Extracting and Cracking Mac OS X Lion Password Hashes [Updated]
The Defence in Depth blog has a post about a flaw in Lion’s redesigned authentication mechanisms and Directory Services. In short, it is possible to change the password of the currently logged in user by simply running the following command in the terminal, and it won’t ask you for the user’s current password:
$ dscl localhost -passwd /Search/Users/<username>
In Lion it is also easy to dump a user’s SHA-512 password hash using the following command:
$ dscl localhost -read /Search/Users/<username>
Then look for the dsAttrTypeNative:ShadowHashData chunk in the output (sample below). The hex string in red is the salt, and the green is the hash.
62706c69 73743030 d101025d 53414c54 45442d53 48413531 324f1044 74911f72 3bd2f66a 3255e0af 4b85c639 776d510b 63f0b939 c432ab6e 082286c4 7586f19b 4e2f3aab 74229ae1 24ccb11e 916a7a1c 9b29c64b d6b0fd6c bd22e7b1 f0ba1673 080b1900 00000000 00010100 00000000 00000300 00000000 00000000 00000000 000060
Cracking password hashes can be done using his custom Python script, or John the Ripper (with the Jumbo patch). Note that even if someone manages to obtain your password hash, if you’re using a strong password it will be extremely difficult for them to recover it. Seems like both of these are important but fairly low-risk flaws introduced into Lion. Hopefully Apple will look into these for the next update.
[Update 1] While waiting for an Apple-supplied security update, it is possible to protect yourself from this vulnerability by adjusting the permissions on dscl:
sudo chmod go-x /usr/bin/dscl
This makes it so that only root can execute dscl. To revert this simply run:
sudo chmod go+x /usr/bin/dscl
[Update 2] This vulnerability was patched in Mac OS X 10.7.2.
Mac App Store Simple Copy Protection Security Bypassed
The Mac App Store was released in the recent 10.6.6 update, allowing Mac users to buy and install apps in the same, easy, one-click fashion as iPhone and iPod Touch users. Over 1 million apps were downloaded in the first 24 hours. Although the Mac App Store doesn’t make use of a sandbox like the iOS App Store does, there are still several mechanisms developers can use to prevent their software from being copied and shared between different users.
Hackers have discovered that one of the simpler methods used to authenticate an app is actually stored as a separate plist file within the application bundle. This means that an app can be copied, and the authentication files within its bundle can be replaced with those from an app that was legally purchased (even if it’s a free app).
In order to resolve this, developers should not rely solely on the data found within the plist file external to the binary, and perform some checks against hard-coded values within the binary itself. Some simple tips are available here. Ultimately all software is crackable, Mac App Store or not, so my suggestion to application developers is: spend more time developing great new features, and less time worrying about anti-piracy. This is what itself Apple does. In the long run most people will follow the simplicity route and buy the app.
In related news: How not to store passwords in iOS (developers take heed)
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