Deep Dive into Azure AD Domain Services – Part 2

Deep Dive into Azure AD Domain Services  – Part 2

Welcome back to part 2 of my series on Microsoft’s managed services offering of Azure Active Directory Domain Services (AAD DS).  In my first post I covered so some of the basic configuration settings of the a default service instance.  In this post I’m going to dig a bit deeper and look at network flows, what type of secure tunnels are available for LDAPS, and examine the authentication protocols and supporting cipher suites are configured for the service.

To perform these tests I leveraged a few different tools.  For a port scanner I used Zenmap.  To examine the protocols and cipher suites supported by the LDAPS service I used a custom openssl binary running on an Ubuntu VM in Azure.  For examination of the authentication protocol support I used Samba’s smbclient running on the Ubuntu VM in combination with WinSCP for file transfer, tcpdump for packet capture, and WireShark for packet analysis.

Let’s start off with examining the open ports since it takes the least amount of effort.  To do that I start up Zenmap and set the target to one of the domain controllers (DCs) IP addresses, choose the intense profile (why not?), and hit scan.  Once the scan is complete the results are displayed.


Navigating to the Ports / Hosts tab displays the open ports. All but one of them are straight out of the standard required ports you’d see open on a Windows Server functioning as an Active Directory DC.  An opened port 443 deserves more investigation.


Let’s start with the obvious and attempt to hit the IP over an HTTPS connection but no luck there.


Let’s break out Fiddler and hit it again.  If we look at the first session where we build the secure tunnel to the website we see some of the details for the certificate being used to secure the session.  Opening the TextView tab of the response shows a Subject of CN=DCaaS Fleet Dc Identity Cert – 0593c62a-e713-4e56-a1be-0ef78f1a2793.  Domain Controller-as-a-Service, I like it Microsoft.  Additionally Fiddler identifies the web platform as the Microsoft HTTP Server API (HTTP.SYS).  Microsoft has been doing a lot more that API since it’s much more lightweight than IIS.  I wanted to take a closer look at the certificate so I opened the website in Dev mode in Chrome and exported it.  The EKUs are normal for a standard use certificate and it’s self-signed and untrusted on my system.  The fact that the certificate is untrusted and Microsoft isn’t rolling it out to domain-joined members tells me whatever service is running on the port isn’t for my consumption.

So what’s running on that port?  I have no idea.  The use of the HTTP Server API and a self-signed certificate with a subject specific to the managed domain service tells me it’s providing access to some type of internal management service Microsoft is using to orchestrate the managed domain controllers.  If anyone has more info on this, I’d love to hear it.


Let’s now take a look at how Microsoft did at securing LDAPS connectivity to the managed domain.  LDAPS is not enabled by default in the managed domain and needs to be configured through the Azure AD Domain Services blade per these instructions.  Oddly enough Microsoft provides an option to expose LDAPS over the Internet.  Why any sane human being would ever do this, I don’t know but we’ll cover that in a later post.

I wanted to test SSLv3 and up and I didn’t want to spend time manipulating registry entries on a Windows client so I decided to spin up an Ubuntu Server 17.10 VM in Azure.  While the Ubuntu VM was spinning up, I created a certificate to be used for LDAPS using the PowerShell command referenced in the Microsoft article and enabled LDAPS through the Azure AD Domain Services resource in the Azure Portal.  I did not enable LDAPS for the Internet for these initial tests.

After adding the certificate used by LDAPS to the trusted certificate store on the Windows Server, I opened LDP.EXE and tried establishing LDAPS connection over port 636 and we get a successful connection.


Once I verified the managed domain was now supporting LDAPS connections I switched over to the Ubuntu box via an SSH session.  Ubuntu removed SSLv3 support in the OpenSSL binary that comes pre-packaged with Ubuntu so to test it I needed to build another OpenSSL binary.  Thankfully some kind soul out there on the Interwebz documented how to do exactly that without overwriting the existing version.  Before I could build a new binary I had to add re-install the Make package and add the Gnu Compiler Collection (GCC) package using the two commands below.

  • sudo apt-get install –reinstall make
  • sudo apt-get install gcc

After the two packages were installed I built the new binary using the instructions in the link, tested the command, and validated the binary now includes SSLv3.


After Poodle hit the news back in 2014, Microsoft along with the rest of the tech industry advised SSLv3 be disabled.  Thankfully this basic well known vulnerability has been covered and SSLv3 is disabled.


SSLv3 is disabled, but what about TLS 1.0, 1.1, and 1.2?  How about the cipher suites?  Are they aligned with NIST guidance?  To test that I used a tool named TestSSLServer by Thomas Pornin.  It’s a simple command line tool which makes cycling through the available cipher suites quick and easy.


The options I chose perform the following actions:

  • -all -> Perform an “exhaustive” search across cipher suites
  • -t 1 -> Space out the connections by one second
  • -min tlsv1 -> Start with TLSv1

The command produces the output below.

server selection: enforce server preferences
3– (key: RSA) RSA_WITH_AES_256_CBC_SHA
3– (key: RSA) RSA_WITH_AES_128_CBC_SHA
3– (key: RSA) RSA_WITH_RC4_128_SHA
3– (key: RSA) RSA_WITH_RC4_128_MD5
TLSv1.1: idem
server selection: enforce server preferences
3f- (key: RSA) ECDHE_RSA_WITH_AES_256_CBC_SHA384
3f- (key: RSA) ECDHE_RSA_WITH_AES_128_CBC_SHA256
3f- (key: RSA) DHE_RSA_WITH_AES_256_GCM_SHA384
3f- (key: RSA) DHE_RSA_WITH_AES_128_GCM_SHA256
3– (key: RSA) RSA_WITH_AES_256_GCM_SHA384
3– (key: RSA) RSA_WITH_AES_128_GCM_SHA256
3– (key: RSA) RSA_WITH_AES_256_CBC_SHA256
3– (key: RSA) RSA_WITH_AES_128_CBC_SHA256
3– (key: RSA) RSA_WITH_AES_256_CBC_SHA
3– (key: RSA) RSA_WITH_AES_128_CBC_SHA
3– (key: RSA) RSA_WITH_RC4_128_SHA
3– (key: RSA) RSA_WITH_RC4_128_MD5

As can be seen from the bolded output above, Microsoft is still supporting the RC4 cipher suites in the managed domain. RC4 has been known to be a vulnerable algorithm for years now and it’s disappointing to see it still supported especially since I haven’t seen any options available to disable within the managed domain. While 3DES still has a fair amount of usage, there have been documented vulnerabilities and NIST plans to disallow it for TLS in the near future. While commercial customers may be more willing to deal with the continued use of these algorithms, government entities will not.

Let’s now jump over to Kerberos and check out what cipher suites are supported by the managed DC. For that we pull up ADUC and check the msDS-SupportedEncryptionTypes attribute of the DC’s computer object. The attribute is set to a value of 28, which is the default for Windows Server 2012 R2 DCs. In ADUC we can see that this value translates to support of the following algorithms:


Again we see more support for RC4 which should be a big no no in the year 2018. This is a risk that orgs using AAD DS will need to live with unless Microsoft adds some options to harden the managed DCs.

Last but not least I was curious if Microsoft had support for NTLMv1. By default Windows Server 2012 R2 supports NTLMv1 due to requirements for backwards compatibility. Microsoft has long recommended disabling NTLMv1 due to the documented issues with the security of the protocol. So has Microsoft followed their own advice in the AAD DS environment?

To check this I’m going use Samba’s smbclient package on the Ubuntu VM. I’ll use smbclient to connect to the DC’s share from the Ubuntu box using the NTLM protocol. Samba has enforced the use NTLMV2 in smbclient by default so I needed to make some modifications to the global section of the smb.conf file by adding client ntlmv2 auth = no. This option disables NTLMv2 on smbclient and will force it to use NTLMv1.


After saving the changes to smb.conf I exit back to the terminal and try opening a connection with smbclient. The options I used do the following:

  • -L -> List the shares on my DC’s IP address
  • -U -> My domain user name
  • -m -> Use the SMB2 protocol


While I ran the command I also did a packet capture using tcpdump which I moved over to my Windows box using WinSCP.  I then opened the capture with WireShark and navigated to the packet containing the Session Setup Request.  In the parsed capture we don’t see an NTLMv2 Response which means NTLMv1 was used to authenticate to the domain controller indicating NTLMv1 is supported by the managed domain controllers.


Based upon what I’ve observed from poking around and running these tests I’m fairly confident Microsoft is using a very out-of-the-box configuration for the managed Windows Active Directory domain.  There doesn’t seem to be much of an attempt to harden the domain against some of the older and well known risks.  I don’t anticipate this offering being very appealing to organizations with strong security requirements.  Microsoft should look to offer some hardening options that would be configurable through the Azure Portal.  Those hardening options are going to need to include some type of access to the logs like I mentioned in my last post.  Anyone who has tried to rid their network of insecure cipher suites or older authentication protocols knows the importance of access to the domain controller logs to the success of that type of effort.

My next post will be the final post in this series.  I’ll cover the option Microsoft provides to expose LDAPS to the Internet (WHY OH WHY WOULD YOU DO THAT?), summarize my findings, and mention a few other interesting things I came across during the study for this series.


Deep Dive into Azure AD Domain Services – Part 1

Deep Dive into Azure AD Domain Services  – Part 1

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!