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Tiny Deathstars of Foulness

I mentioned mdmclient when I gave the talk on the inner workings of Mobile Device Management, or MDM. There, I spent a lot of time on APNs and profiles, but just kinda’ spoke about mdmclient in terms of it being the agent that runs on macOS to provide mdm parity for the Mac. The mdmclient binary is located at /usr/libexec/mdmclient and provides pretty limited access to see how the Mac reacts to and interprets information coming from a device management provider.

I had been meaning to do a write-up on mdmclient and document what it can do since it first shipped. But as luck would have it, @Mosen on the Slacks beat me to the punch with a fantastic resource at https://mosen.github.io/profiledocs/troubleshooting/mdmclient.html. So here I’d like to focus on just 3 examples of using mdmclient. The first is to see what insight an MDM has to the applications installed (whether that information is actually committed to a database somewhere or not) using QueryInstalledApps:

/usr/libexec/mdmclient QueryInstalledApps

Here, we can see an array output of each bundle installed:

{BundleSize = 27457223;
Identifier = “com.hipchat.HipChat”;
Name = HipChat;
ShortVersion = “3.1.6”;
Version = “3.1.6”;}

Now, we can end up with duplicates, and so focus on just the unique Identifier keys, as follows:

/usr/libexec/mdmclient QueryInstalledApps | grep Identifier | uniq

The second iteration is to see installed profiles. The most basic of these, is to see user profiles, which can be obtained using QueryInstalledProfiles, as follows:

/usr/libexec/mdmclient QueryInstalledProfiles

Now, I could see using the profiles command with the -L option that I have a profile to configure office365 on my machine:

profiles -L

charlesedge[1] attribute: profileIdentifier: com.jamfsw.office365.a5f0e328-ea86-11e3-a26c-6476bab5f328
There are 1 user configuration profiles installed for ‘charlesedge’

So to see what that same information looks like, when queried from an MDM solution:
/usr/libexec/mdmclient QueryInstalledProfiles

QueryInstalledProfiles then returns:

({HasRemovalPasscode = 0;
IsEncrypted = 0;
PayloadContent = (
{PayloadDisplayName = “Charles Edge’s Office 365”;
PayloadIdentifier = “com.jamfsw.office365.a5f0e328-ea86-11e3-a26c-6476bab5f328.exchange.a5f2ccd9-ea86-11e3-b1e0-6476bab5f328”;
PayloadType = “com.apple.ews.account”;
PayloadUUID = “a5f2ccd9-ea86-11e3-b1e0-6476bab5f328”;
PayloadVersion = 1;});
PayloadDescription = “This will configure your Office 365 account for your Mac.”;
PayloadDisplayName = “Charles Edge’s Office 365”;
PayloadIdentifier = “com.jamfsw.office365.a5f0e328-ea86-11e3-a26c-6476bab5f328”;
PayloadOrganization = “JAMF Software”;
PayloadRemovalDisallowed = 0;
PayloadUUID = “a5f0e328-ea86-11e3-a26c-6476bab5f328”;
PayloadVersion = 1;
SignerCertificates = ();})

You can then take action based on this type of information, allow you to either fill a database for agent-based management, or simply take action if something is missing, etc.

QueryInstalledProfiles covers user profiles. To see system, you’ll need installedProfiles:

/usr/libexec/mdmclient installedProfiles | grep "Profile Name"

Run without the grep for a considerably more verbose amount of information.

Finally, let’s look at one more piece of information, which is the hash for the iTunes Store. That’s a point I’ve made a number of times, that the iTunes account email address is never provided to an MDM, once associated to a device or user on a device. Instead, there’s a hash of the account. These are important with VPP, as it allows for reversing (according to the MDM) which users have claimed which apps, or which users are using a given app, as well as how many devices they’re accessing those from. To see a hash, as an MDM sees it:

/usr/libexec/mdmclient QueryAppInstallation | grep iTunesStoreAccountHash

There’s a lot more you can do here, and I’m sure we’ll see a lot more over time. However, the work from @mosen combined with the opening up of the documentation on profiles and the mdm protocol helps to shed some light on how things work under the hood, and how we can use these features to provide greater programatic management for the Mac.

For example, to grab that iTuneshash from earlier, as a Jamf extension attribute you could use the following: https://github.com/krypted/ituneshash/blob/master/ituneshash.sh

April 28th, 2017

Posted In: Mac OS X, Mac OS X Server, Mac Security

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