# MacOS MDM

## Basics

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

[Mobile Device Management](https://en.wikipedia.org/wiki/Mobile\_device\_management) (MDM) is a technology commonly used to **administer end-user computing devices** such as mobile phones, laptops, desktops and tablets. In the case of Apple platforms like iOS, macOS and tvOS, it refers to a specific set of features, APIs and techniques used by administrators to manage these devices. Management of devices via MDM requires a compatible commercial or open-source MDM server that implements support for the [MDM Protocol](https://developer.apple.com/enterprise/documentation/MDM-Protocol-Reference.pdf).

* 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)?

The [Device Enrollment Program](https://www.apple.com/business/site/docs/DEP\_Guide.pdf) (DEP) is a service offered by Apple that **simplifies** Mobile Device Management (MDM) **enrollment** by offering **zero-touch configuration** of iOS, macOS, and tvOS devices. Unlike more traditional deployment methods, which require the end-user or administrator to take action to configure a device, or manually enroll with an MDM server, DEP aims to bootstrap this process, **allowing the user to unbox a new Apple device and have it configured for use in the organization almost immediately**.

Administrators can leverage DEP to automatically enroll devices in their organization’s MDM server. Once a device is enrolled, **in many cases it is treated as a “trusted”** device owned by the organization, and could receive any number of certificates, applications, WiFi passwords, VPN configurations [and so on](https://developer.apple.com/enterprise/documentation/Configuration-Profile-Reference.pdf).

* 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)

{% hint style="danger" %}
Unfortunately, if an organization has not taken additional steps to **protect their MDM enrollment**, a simplified end-user enrollment process through DEP can also mean a simplified process for **attackers to enroll a device of their choosing in the organization’s MDM** server, assuming the "identity" of a corporate device.
{% endhint %}

### 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):
  * The so-called [DEP "cloud service" API](https://developer.apple.com/enterprise/documentation/MDM-Protocol-Reference.pdf). This is used by MDM servers to associate DEP profiles with specific devices.
  * The [DEP API used by Apple Authorized Resellers](https://applecareconnect.apple.com/api-docs/depuat/html/WSImpManual.html) to enroll devices, check enrollment status, and check transaction status.
  * The undocumented private DEP API. This is used by Apple Devices to request their DEP profile. On macOS, the `cloudconfigurationd` binary is responsible for communicating over this API.
* 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 (564).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 (568).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&#x20;

![](<../../../.gitbook/assets/image (566) (1).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 (567).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 (567) (1) (2) (2) (2) (2) (2) (2) (2) (1) (2).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

## Attacks

### Enrolling Devices in Other Organisations

As previously commented, in order to try to enrol a device into an organization **only a Serial Number belonging to that Organization is needed**. Once the device is enrolled, several organizations will install sensitive data on the new device: certificates, applications, WiFi passwords, VPN configurations [and so on](https://developer.apple.com/enterprise/documentation/Configuration-Profile-Reference.pdf).\
Therefore, this could be a dangerous entrypoint for attackers if the enrolment process isn't correctly protected:

{% content-ref url="enrolling-devices-in-other-organisations.md" %}
[enrolling-devices-in-other-organisations.md](enrolling-devices-in-other-organisations.md)
{% endcontent-ref %}

## **References**

* [https://www.youtube.com/watch?v=ku8jZe-MHUU](https://www.youtube.com/watch?v=ku8jZe-MHUU)
* [https://duo.com/labs/research/mdm-me-maybe](https://duo.com/labs/research/mdm-me-maybe)