# MacOS MDM

## Basics

### What is MDM \(Mobile Device Management\)?

* A way to achieve **centralized device management**
* Requires an **MDM server** which implements support for the MDM protocol
* MDM server can **send MDM commands**, such as remote wipe or “install this config”

### Basics What is DEP \(Device Enrolment Program\)?

* Allows a device to automatically enroll in pre-configured MDM server the **first time it’s powered** on
* Most useful when the **device** is **brand new**
* Can also be useful for **reprovisioning** workflows \(**wiped** with fresh install of the OS\)

### Basics What is SCEP \(Simple Certificate Enrolment Protocol\)?

* A relatively old protocol, created before TLS and HTTPS were widespread.
* Gives clients a standardized way of sending a **Certificate Signing Request** \(CSR\) for the purpose of being granted a certificate. The client will ask the server to give him a signed certificate.

### What are Configuration Profiles \(aka mobileconfigs\)?

* Apple’s official way of **setting/enforcing system configuration.**
* File format that can contain multiple payloads.
* Based on property lists \(the XML kind\).
* “can be signed and encrypted to validate their origin, ensure their integrity, and protect their contents.” Basics — Page 70, iOS Security Guide, January 2018.

## Protocols

### MDM

* Combination of APNs \(**Apple server**s\) + RESTful API \(**MDM** **vendor** servers\)
* **Communication** occurs between a **device** and a server associated with a **device** **management** **product**
* **Commands** delivered from the MDM to the device in **plist-encoded dictionaries**
* All over **HTTPS**. MDM servers can be \(and are usually\) pinned.
* Apple grants the MDM vendor an **APNs certificate** for authentication

### DEP

* **3 APIs**: 1 for resellers, 1 for MDM vendors, 1 for device identity \(undocumented\)
* More modern and **JSON** based \(vs. plist\)
* Apple grants an **OAuth token** to the MDM vendor

#### DEP "cloud service" API

* RESTful
* sync device records from Apple to the MDM server
* sync “DEP profiles” to Apple from the MDM server \(delivered by Apple to the device later on\)
* A DEP “profile” contains:
  * MDM vendor server URL
  * Additional trusted certificates for server URL \(optional pinning\)
  * Extra settings \(e.g. which screens to skip in Setup Assistant\)

## Steps for enrolment and management

1. Device record creation \(Reseller, Apple\): The record for the new device is created
2. Device record assignment \(Customer\): The device is assigned to a MDM server
3. Device record sync \(MDM vendor\): MDM sync the device records and push the DEP profiles to Apple
4. DEP check-in \(Device\): Device gets his DEP profile
5. Profile retrieval \(Device\)
6. Profile installation \(Device\) a. incl. MDM, SCEP and root CA payloads
7. MDM command issuance \(Device\)

![](../../.gitbook/assets/image%20%28564%29.png)

The file `/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/System/Library/PrivateFrameworks/ConfigurationProfiles.framework/ConfigurationProfiles.tbd` exports functions that can be considered **high-level "steps"** of the enrolment process.

### Step 4: DEP check-in - Getting the Activation Record

This part of the process occurs when a **user boots a Mac for the first time** \(or after a complete wipe\)

![](../../.gitbook/assets/image%20%28568%29.png)

or when executing `sudo profiles show -type enrollment`

* Determine **whether device is DEP enabled**
* Activation Record is the internal name for **DEP “profile”**
* Begins as soon as the device is connected to Internet
* Driven by **`CPFetchActivationRecord`**
* Implemented by **`cloudconfigurationd`** via XPC. The **"Setup Assistant**" \(when the device is firstly booted\) or the **`profiles`** command will **contact this daemon** to retrieve the activation record.
  * LaunchDaemon \(always runs as root\)

It follows a few steps to get the Activation Record performed by **`MCTeslaConfigurationFetcher`**. This process uses an encryption called **Absinthe**

1. Retrieve **certificate**
   1. GET [https://iprofiles.apple.com/resource/certificate.cer](https://iprofiles.apple.com/resource/certificate.cer)
2. **Initialize** state from certificate \(**`NACInit`**\)
   1. Uses various device-specific data \(i.e. **Serial Number via `IOKit`**\)
3. Retrieve **session key**
   1. POST [https://iprofiles.apple.com/session](https://iprofiles.apple.com/session)
4. Establish the session \(**`NACKeyEstablishment`**\)
5. Make the request
   1. POST to [https://iprofiles.apple.com/macProfile](https://iprofiles.apple.com/macProfile) sending the data `{ "action": "RequestProfileConfiguration", "sn": "" }`
   2. The JSON payload is encrypted using Absinthe \(**`NACSign`**\)
   3. All requests over HTTPs, built-in root certificates are used 

![](../../.gitbook/assets/image%20%28563%29.png)

The response is a JSON dictionary with some important data like:

* **url**: URL of the MDM vendor host for the activation profile
* **anchor-certs**: Array of DER certificates used as trusted anchors

### **Step 5: Profile Retrieval**

![](../../.gitbook/assets/image%20%28569%29.png)

* Request sent to **url provided in DEP profile**.
* **Anchor certificates** are used to **evaluate trust** if provided.
  * Reminder: the **anchor\_certs** property of the DEP profile
* **Request is a simple .plist** with device identification
  * Examples: **UDID, OS version**.
* CMS-signed, DER-encoded
* Signed using the **device identity certificate \(from APNS\)**
* **Certificate chain** includes expired **Apple iPhone Device CA**

![](../../.gitbook/assets/image%20%28570%29.png)

### Step 6: Profile Installation

* Once retrieved, **profile is stored on the system**
* This step begins automatically \(if in **setup assistant**\)
* Driven by **`CPInstallActivationProfile`**
* Implemented by mdmclient over XPC
  * LaunchDaemon \(as root\) or LaunchAgent \(as user\), depending on context
* Configuration profiles have multiple payloads to install
* Framework has a plugin-based architecture for installing profiles
* Each payload type is associated with a plugin
  * Can be XPC \(in framework\) or classic Cocoa \(in ManagedClient.app\)
* Example:
  * Certificate Payloads use CertificateService.xpc

Typically, **activation profile** provided by an MDM vendor will **include the following payloads**:

* `com.apple.mdm`: to **enroll** the device in MDM
* `com.apple.security.scep`: to securely provide a **client certificate** to the device.
* `com.apple.security.pem`: to **install trusted CA certificates** to the device’s System Keychain.
* Installing the MDM payload equivalent to **MDM check-in in the documentation**
* Payload **contains key properties**:
* * MDM Check-In URL \(**`CheckInURL`**\)
  * MDM Command Polling URL \(**`ServerURL`**\) + APNs topic to trigger it
* To install MDM payload, request is sent to **`CheckInURL`**
* Implemented in **`mdmclient`**
* MDM payload can depend on other payloads
* Allows **requests to be pinned to specific certificates**:
  * Property: **`CheckInURLPinningCertificateUUIDs`**
  * Property: **`ServerURLPinningCertificateUUIDs`**
  * Delivered via PEM payload
* Allows device to be attributed with an identity certificate:
  * Property: IdentityCertificateUUID
  * Delivered via SCEP payload

### **Step 7: Listening for MDM commands**

* After MDM check-in is complete, vendor can **issue push notifications using APNs**
* Upon receipt, handled by **`mdmclient`**
* To poll for MDM commands, request is sent to ServerURL
* Makes use of previously installed MDM payload:
  * **`ServerURLPinningCertificateUUIDs`** for pinning request
  * **`IdentityCertificateUUID`** for TLS client certificate

## **References**

* [https://www.youtube.com/watch?v=ku8jZe-MHUU](https://www.youtube.com/watch?v=ku8jZe-MHUU)