Hi everyone. In this series of posts I’ll be doing a deep dive into Microsoft’s Azure AD Domain Services (AAD DS). AAD DS is Microsoft’s managed Windows Active Directory service offered in Microsoft Azure Infrastructure-as-a-Service intended to compete with similar offerings such as Amazon Web Services’s (AWS) Microsoft Active Directory. Microsoft’s solution differs from other offerings in that it sources its user and group information from Azure Active Directory versus an on-premises Windows Active Directory or LDAP.
Like its competitors Microsoft realizes there are still a lot of organizations out there who are still very much attached to legacy on-premises protocols such as NTLM, Kerberos, and LDAP. Not every organization (unfortunately) is ready or able to evolve its applications to consume SAML, Open ID Connect, OAuth, and Rest-Based APIs (yes COTS vendors I’m talking to you and your continued reliance on LDAP authentication in the year 2018). If the service has to be there, it makes sense to consume a managed service so staff can focus less on maintaining legacy technology like Windows Active Directory and focus more on a modern Identity-as-a-Service (IDaaS), Software-as-a-Service (SaaS), and Platform-as-a-Service (Paas) solutions.
Sounds great right? Sure, but how does it work? Microsoft’s documentation does a reasonable job giving the high level details of the service so I encourage you to read through it at some point. I won’t be covering information included in that documentation unless I notice a discrepancy or an area that could use more detail. Instead, I’m going to focus on the areas which I feel are important to understand if you’re going to attempt to consume the service in the same way you would a traditional on-premises Windows Active Directory.
With that introduction, let’s dig in.
The first thing I did was to install the Remote Server Administration Tools (RSAT) for Active Directory Domain Services and Group Policy Management tools. I used these tools to explore some of the configuration choices Microsoft made in the managed service. I also installed Microsoft Network Monitor 3.4 to review packet captures captured using the netsh.
After the tools were installed I started a persistent network capture using netsh using an elevated command prompt. This is an incredibly useful feature of Windows when you need to debug issues that occur prior or during user or system logon. I’ve used this for years to troubleshoot a number of Windows Active Directory issues including slow logons and failed logons. The only downfall of this is you’re forced into using Microsoft Network Monitor or Microsoft Message Analyzer to review the packet captures it creates. While Microsoft Message Analyzer is a sleek tool, the resources required to run it effectively are typically a non-starter for a lab or traditional work laptop so I tend to use Network Monitor.
After the packet capture was started I went through the standard process of joining the machine to the domain and rebooting the computer. After reboot, I logged in an account in the AAD DC Administrators Azure Active Directory group, started an elevated command prompt as the VM’s local administrator and stopped the packet capture. This provided me with a capture of the domain join, initial computer authentication, and initial user authentication.
While I know you’re as eager to dig into the packet capture as I am, I’ll cover that in a future post. Instead I decided to break out the RSAT tools and poke around at configuration choices an administrator would normally make when building out a Windows Active Directory domain.
Let’s first open the tool everyone who touches Windows Active Directory is familiar with, Active Directory Users and Computers (ADUC). The data layout (with Advanced Features option on) for organizational units (OUs) and containers looks very similar to what we’re used to seeing with the exception of the AADC Computers, AADC Users, AADDSDomainAdmin OUs, and AADDSDomainConfig container. I’ll get into these containers in a minute.
If we right-click the domain node and go to properties we see that the domain and forest are running in Windows Server 2012 R2 domain and forest functional level with no trusts defined. Examining the operating system tab of the two domain controllers in the Domain Controllers OU shows that both boxes run Windows Server 2012 R2. Interesting that Microsoft chose not to use Windows Server 2016.
Navigating to the Security tab and clicking the Advanced button shows that the AAD DC Administrator group has only been granted the Create Organizational Unit objects permission while the AAD DC Service Accounts group has been granted Replicating Directory Changes. As you can see from these permissions the base of the directory tree is very locked down.
Let me circle back to the OUs and Containers I talked about above. The AADDC Computers and AADDC Users OUs are the default OUs Microsoft creates for you. Newly joined machines are added to the AADDC Computers OU and users synchronized from the Azure AD tenant are placed in the AADDC Users OU. As we saw from the permissions above, we could use an account in the AAD DC Administrators group to create additional OUs under the domain node to delegate control to another set of more restricted admins, for the purposes of controlling GPOs if security filtering doesn’t meet our requirements, or for creating additional service accounts or groups for the workloads we deploy in the environment. The permissions within the default OUs are very limited. In the AADDC Computer OU GPOs can be applied and computer objects can be added and removed. In the AADC Users OU only GPOs can be applied which makes sense considering the user and group objects stored there are sourced from your authoritative Azure AD tenant.
The AADDSDomainAdmin OU contains a single security group named AADDS Service Administrators Group (pre-Windows 2000 name of AADDSDomAdmGroup). The group contains a single member names dcaasadmin which is the renamed built-in Active Directory administrator account. The group is nested into a number of highly privileged built-in Active Directory groups including Administrators, Domain Admins, Domain Users, Enterprise Admins, and Schema Admins. I’m very uncomfortable with Microsoft’s choice to make a “god” group and even a “god” user of the built-in administrator. This directly conflicts with security best practices for Active Directory which would see no account being a permanent member of these highly privileged groups or at the least divvying up the privileges among separate security principals. I would have liked to see Microsoft leverage a Red Forest Red Forest design here. Hopefully we’ll see some improvements as the service matures. I’m unsure as to the purpose of the OU and this group at this time.
The AADDSDomainConfig container contains a single container object named SchemaUpdate. I reviewed the attributes of both containers hoping to glean some idea of the purpose of the containers and the only thing I saw of notice was the revision attribute was set to 2. Maybe Microsoft is tracking the schema of their standard managed domain image via this attribute? In a future post in this series I’ll do a comparison of this managed domain’s schema with a fresh Windows Server 2012 R2 schema.
Opening Active Directory Sites and Services shows that Microsoft has chosen to leave the domain with a single site. This design choice makes sense given that a limitation of AAD DS is that it can only serve a single region. If that limitation is ever lifted, Microsoft will need to revisit this choice and perhaps include a site for each region. Expanding the Default-First-Site-Name site and the Servers node shows the two domain controllers Microsoft is using to provide the Windows Active Directory service to the VNet.
So the layout is simple, what about the group policy objects (GPO)? Opening up the Group Policy Management Console displays five GPOs which are included in every managed domain.
The AADDC Users GPO is empty of settings while the AADC Computers GPO has a single Preference defined that adds the AAD DC Administrators group to the built-in Administrators group on any member servers added to the OU. The Default Domain Controllers Policy (DDCP) GPO is your standard out of the box DDCP with nothing special set. The Default Domain Policy (DDP) GPO on the other hand has a number of settings applied. The password policy is interesting… I get that you have the option to source all the user accounts within your AAD DS domain from Azure AD, but Microsoft is still giving you the ability to create user accounts in the managed domain as I covered above which makes me uncomfortable with the default password policy. Microsoft hasn’t delegated the ability to create Fine Grained Password Policies (FGPPs) either, which means you’re stuck with this very lax password policy. Given the lack of technical enforcement, I’d recommend avoiding creating user accounts directly in the managed domain for any purpose until Microsoft delegates the ability to create FGPPs. The remaining settings in the policy are standard out of the box DDP.
The GPO named Event Log GPO is linked to the Domain Controllers OU and executes a startup script named EventLogRetentionPolicy.PS1. Being the nosy geek I am, I dug through SYSVOL to find the script. The script is very simple in that it sets each event log to overwrite events over 31 days old. It then verifies the results and prints the results to the console. Event logs are an interesting beast in AAD DS. An account in the AAD DC Administrators group doesn’t have the right to connect to the Event Logs on the DCs remotely and I haven’t come across any options to view those logs. I don’t see any mention of them in the Microsoft documentation, so my assumption is you don’t get access to them at this time. I have to imagine this is a show stopper for some organizations considering the critical importance of Domain Controller logs. If anyone knows how to access these logs, please let me know. I’d like to see Microsoft incorporate an option to send the logs to a syslog agent via a configuration option in the Azure AD Domain Services blade in the Azure Portal.
I’m going to stop here today. In my next post I’ll do some poking around by running a port scan against the managed domain controllers to see what network flows are open, enable LDAPS to see what the SSL/TLS landscape looks like, and examine authentication protocols and algorithms supported (NTLMv1,v2, Kerberos DES, etc). Thanks for reading!