Hello my fellow geeks! It’s been a while since my last post. I took on a new role recently and have been very busy getting up to speed. I finally have enough breathing room where I’ll have some time to work on some new posts.
Hello my fellow geeks! It’s been a while since my last post. I took on a new role recently and have been very busy getting up to speed. I finally have enough breathing room where I’ll have some time to work on some new posts.
Over the past year I’ve done deep dives into both Amazon’s AWS Managed Microsoft Active Directory and Microsoft’s Azure Active Directory Domain Services. These services represent each vendor’s offering of a managed Windows Active Directory (AD) service. I extensively covered the benefits of a service over the course of the posts, so today I’m going to cover the key features of each service. I’m also going to include two tables. One table will outline the differences in general features while the other outlines the differences in security-related features.
Let’s hit on the key points first.
Here is a table showing the comparison of general features:
|Features||AWS Managed Microsoft AD||Azure Active Directory Domain Services|
|Cost Basis||Number of Domain Controllers||Number of Directory Objects|
|Schema Extensions||Yes, with limitations||No|
|Trusts||Yes, with limitations||No|
|Domain Controller Log Access||Security and DNS Server Event Logs||No|
|Limit of Managed Forests||10 per account||1 per Azure AD tenant|
|Supports being used on-premises||Yes with Direct Connect or VPN||No, within VNet only|
|Scaled By Customer||Yes||No|
|Max number of Domain Controller||20 per directory||Unknown how service is scaled|
Here is a table of security capabilities:
|Features||AWS Managed Microsoft AD||Azure Active Directory Domain Services|
|Requires Directory Synchronization||No||Yes, including password|
|Fine-Grained Password Policies||Yes, limited to seven||No|
|Smart Card Authentication||Not native, requires RADIUS||No|
|LDAPS||Yes, with special requirements||Yes, but LDAP operations are limited to read|
|LDAPS Protocols||SSLv3, TLS 1.0, TLS 1.2||TLS 1.0, TLS 1.2|
|LDAPS Cipher Suites||RC4, 3DES, AES128, AES256||RC4, 3DES, AES128, AES256|
|Kerberos Delegation||Account-Based and Resource-Based||Resource-Based|
|Kerberos Encryption||RC4, AES128, AES256||RC4, AES128, AES256|
|NTLM Support||NTLMv1, NTLMv2||NTLMv1, NTLMv2|
Well folks that sums it up. As you can see from both of the series as well as this summary post both vendors have taken very different approaches in providing the service. It will be interesting to see how these offerings evolve over the next few years. As much as we’d love to see Windows Active Directory go away, it will still be here for years to come.
Until next time my fellow geeks!
Welcome back fellow geek. Today I’m continuing my deep dive series into AWS Managed Microsoft AD. This will represent the seventh post in the series and I’ve covered some great content over the series including:
Today I’m going cover three additional capabilities of AWS Managed Microsoft AD which includes the creation of trusts, access to the Domain Controller event logs, and scalability.
I’ll first cover the capabilities around Active Directory trusts. Providing this capability opens up the possibility a number of scenarios that aren’t possible in managed Windows Active Directory (Windows AD) services that don’t support trusts such as Microsoft’s Azure Active Directory Domain Services. Some of the scenarios that pop up in my head are resource forest, trusts with trusted partners to maintain collaboration for legacy applications (applications dependent on legacy protocols such as Kerberos/NTLM/LDAP), trusts between development, QA, and production forests, and the usage of features features such as selective authentication to mitigate the risk to on-premises infrastructure.
For many organizations, modernization of an entire application catalog isn’t feasible but those organizations still want to take advantage of the cost and security benefits of cloud services. This is where AWS Managed Microsoft AD can really shine. It’s capability to support Active Directory forests trusts opens up the opportunity for those organizations to extend their identity boundary to the cloud while supporting legacy infrastructure. Existing on-premises core infrastructure services such as PKI and SIEM can continue to be used and even extended to monitor the infrastructure using the managed Windows AD.
As you can see this is an extremely powerful capability and makes the service a good for almost every Windows AD scenario. So that’s all well and good, but if you wanted marketing material you’d be reading the official documentation right? You came here for the deep dive, so let’s get into it.
The first thing that popped into my mind was the question as to how Amazon would be providing this capability in a managed service model. Creating a forest trust typically requires membership in privileged groups such as Enterprise Admins and Domain Admins, which obviously isn’t possible in a manged service. I’m sure it’s possible to delegate the creation of Active Directory trusts and DNS conditional forwarders with modifications of directory permissions and possibly user rights, but there’s a better way. What is this better way you may be asking yourself? Perhaps serving it up via the Directory Services console in the same way schema modifications are served up?
Let’s walk through the process of setting up an Active Directory forest trust with a customer-managed traditional implementation of Windows Active Directory and an instance of AWS Managed Microsoft AD. For this I’ll be leveraging my home Hyper-V lab. I’m actually in the process of rebuilding it so there isn’t much there right now. The home lab consists of two virtual machines, one named JOG-DC running Windows Server 2016 and functions as a domain controller (AD DS) and certificate authority (AD CS) for the journeyofthegeek.com Active Directory forest. The other virtual machine is named named JOG-CLIENT, runs Windows 10, and is joined to the journeyofthegeek.com domain. I’ve connected my VPC with my home lab using AWS’s Managed VPN to setup a site-to-site IPSec VPN connection with my local pfSense box.
Prior to setting up the trusts there are a few preparatory steps that need to be completed. The steps will be familiar to those of you who have established forests trusts across firewalled network segments. At a high level, you’ll want to perform the following tasks:
For the first step I played it lazy since this is is a temporary configuration (please don’t do this in production). I allowed all traffic from the VPC address range to my lab environment by modifying the firewall rules on my pfSense box. On the AWS side I needed to adjust the traffic rules for the security group SERVER01 is in as well as the security group for the managed domain controllers.
To establish DNS resolution between the two forests I’ll be using conditional forwarders setup within each forest. Setting the conditional forwarders up in the journeyofthegeek.com forest means I have to locate the IP addresses of the managed domain controllers in AWS. There are a few ways you could do it, but I went to the AWS Directory Services Console and selected the geekintheweeds.com directory.
On the Directory details section of the console the DNS addresses list the IP addresses the domain controllers are using.
After creating the conditional forwarder in the DNS Management MMC in the journeyofthegeek.com forest, DNS resolution of a domain controller from geekintheweeds.com was successful.
I next created the trust in the journeyofthegeek.com domain ensuring to select the option to create the trust in this domain only and recording the trust password using the Active Directory Domains and Trusts. We can’t create the trusts in both domains since we don’t have an account with the appropriate privileges in the AWS managed domain.
Next up I bounced back over to the Directory Services console and selected the geekintheweeds.com directory. From there I selected the Network & security tab to open the menu needed to create the trust.
From here I clicked the Add trust relationship button which brings up the Add a trust relationship menu. Here I filled in the name of the domain I want to establish the trust with, the trust password I setup in the journeyofthegeek.com domain, select a two-way trust, and add an IP that will be used within configuration of the conditional forwarder setup by the managed service.
After clicking the Add button the status of the trust is updated to Creating.
The process takes a few minutes after which the status reports as verified.
Opening up the Active Directory Users and Computers (ADUC) MMC in the journeyofthegeek.com domain and selecting the geekintheweeds.com domain successfully displays the directory structure. Trying the opposite in the geekintheweeds.com domain works correctly as well. So our two-way trust has been created successfully. We would now have the ability to setup any of the scenarios I talked about earlier in the post including a resource forest or leveraging the managed domain as a primary Windows AD service for on-premises infrastructure.
The second capability I want to briefly touch on is the ability to view the Security Event Log and DNS Server logs on the managed domain controllers. Unlike Microsoft’s managed Windows AD service, Amazon provides ongoing access to the Security Event Log and DNS Server Log. The logs can be viewed using the Event Log MMC from a domain-joined machine or programmatically with PowerShell. The group policy assigned to the Domain Controllers OU enforces a maximum event log size of 256MB but Amazon also archives a year’s worth of logs which can be requested in the event of an incident. The lack of this capability was a big sore spot for me when I looked at Azure Active Directory Domain Services. It’s great to see Amazon has identified this critical use case.
Last but definitely not least, let’s quickly cover the scalability of the service. Follow Microsoft best practices and you can take full advantage of scaling horizontally with the click of a single button. Be aware that the service only scales horizontally and not vertically. If you have applications that don’t follow best practices and point to specific domain controllers or perform extremely inefficient LDAP queries (yes I’m talking to you developers who perform searches using front and rear-facing wildcards and use LDAP_MATCHING_RULE_IN_CHAIN filters) horizontal scaling isn’t going to help you.
Well folks that rounds out this entry into the series. As we saw in the post Amazon has added key capabilities that Microsoft’s managed service is missing right now. This makes AWS Managed Microsoft AD the more versatile of the two services and more than likely a better fit in almost any scenario where there is a reliance on Windows AD.
In my final posts of the series I’ll provide a comparison chart showing the differing capabilities of both AWS and Microsoft’s services.
See you next post!
Yes folks, we’re at the six post for the series on AWS Managed Microsoft AD (AWS Managed AD. I’ve covered a lot of material over the series including an overview, how to setup the service, the directory structure, pre-configured security principals, group policies, and the delegated security model, how to configure LDAPS in the service and the implications of Amazon’s design, and just a few days ago looked at the configuration of the security of the service in regards to protocols and cipher suites. As per usual, I’d highly suggest you take a read through the prior posts in the series before starting on this one.
Today I’m going to look the capabilities within the AWS Managed AD to handle Active Directory schema modifications. If you’ve read my series on Microsoft’s Azure Active Directory Domain Services (AAD DS) you know that the service doesn’t support the schema modifications. This makes Amazon’s service the better offering in an environment where schema modifications to the standard Windows AD schema are a requirement. However, like many capabilities in a managed Windows Active Directory (Windows AD) service, limitations are introduced when compared to a customer-run Windows Active Directory infrastructure.
If you’ve administered an Active Directory environment in a complex enterprise (managing users, groups, and group policies doesn’t count) you’re familiar with the butterflies that accompany the mention of a schema change. Modifying the schema of Active Directory is similar to modifying the DNA of a living being. Sure, you might have wonderful intentions but you may just end up causing the zombie apocalypse. Modifications typically mean lots of application testing of the schema changes in a lower environment and a well documented and disaster recovery plan (you really don’t want to try to recover from a failed schema change or have to back one out).
Given the above, you can see the logic of why a service provider providing a managed Windows AD service wouldn’t want to allow schema changes. However, there very legitimate business justifications for expanding the schema (outside your standard AD/Exchange/Skype upgrades) such as applications that need to store additional data about a security principal or having a business process that would be better facilitated with some additional metadata attached to an employee’s AD user account. This is the market share Amazon is looking to capture.
So how does Amazon provide for this capability in a managed Windows AD forest? Amazon accomplishes it through a very intelligent method of performing such a critical activity. It’s accomplished by submitting an LDIF through the AWS Directory Service console. That’s right folks, you (and probably more so Amazon) doesn’t have to worry about you as the customer having to hold membership in a highly privileged group such as Schema Admins or absolutely butchering a schema change by modifying something you didn’t intend to modify.
Amazon describes three steps to modifying the schema:
Let’s review each of the steps.
In the first step we have to create a LDAP Data Interchange Format (LDIF) file. Think of the LDIF file as a set of instructions to the directory which in this could would be an add or modify to an object class or attribute. I’ll be using a sample LDIF file I grabbed from an Oracle knowledge base article. This schema file will add the attributes of unixUserName, unixGroupName, and unixNameIinfo to the default Active Directory schema.
To complete step one I dumped the contents below into an LDIF file and saved it as schemamod.ldif.
dn: CN=unixUserName, CN=Schema, CN=Configuration, DC=example, DC=com changetype: add attributeID: 220.127.116.11.18.104.22.168.22.214.171.124 attributeSyntax: 126.96.36.199 isSingleValued: TRUE searchFlags: 1 lDAPDisplayName: unixUserName adminDescription: This attribute contains the object's UNIX username objectClass: attributeSchema oMSyntax: 27 dn: CN=unixGroupName, CN=Schema, CN=Configuration, DC=example, DC=com changetype: add attributeID: 188.8.131.52.184.108.40.206.220.127.116.11 attributeSyntax: 18.104.22.168 isSingleValued: TRUE searchFlags: 1 lDAPDisplayName: unixGroupName adminDescription: This attribute contains the object's UNIX groupname objectClass: attributeSchema oMSyntax: 27 dn: changetype: modify add: schemaUpdateNow schemaUpdateNow: 1 - dn: CN=unixNameInfo, CN=Schema, CN=Configuration, DC=example, DC=com changetype: add governsID: 22.214.171.124.126.96.36.199.188.8.131.52 lDAPDisplayName: unixNameInfo adminDescription: Auxiliary class to store UNIX name info in AD mayContain: unixUserName mayContain: unixGroupName objectClass: classSchema objectClassCategory: 3 subClassOf: top
For the step two I logged into the AWS Management Console and navigated to the Directory Service Console. Here we can see my instance AWS Managed AD with the domain name of geekintheweeds.com.
I then clicked hyperlink on my Directory ID which takes me into the console for the geekintheweeds.com instance. Scrolling down shows a menu where a number of operations can be performed. For the purposes of this blog post, we’re going to focus on the Maintenance menu item. Here we the ability to leverage AWS Simple Notification Service (AWS SNS) to create notifications for directory changes such as health changes where a managed Domain Controller goes down. The second section is a pretty neat feature where we can snapshot the Windows AD environment to create a point-in-time copy of the directory we can restore. We’ll see this in action in a few minutes. Lastly, we have the schema extensions section.
Here I clicked the Upload and update schema button and entered selected the LDIF file and added a short description. I then clicked the Update Schema button.
If you know me you know I love to try to break stuff. If you look closely at the LDIF contents I pasted above you’ll notice I didn’t update the file with my domain name. Here the error in the LDIF has been detected and the schema modification was cancelled.
I went through made the necessary modifications to the file and tried again. The LDIF processes through and the console updates to show the schema change has been initialized.
Hitting refresh on the browser window updates the status to show Creating Snapshot. Yes folks Amazon has baked into the schema update process a snapshot of the directory provide a fallback mechanism in the event of your zombie apocalypse. The snapshot creation process will take a while.
While the snapshot process, let’s discuss what Amazon is doing behind the scenes to process the LDIF file. We first saw that it performs some light validation on the LDIF file, it then takes a snapshot of the directory, then applies to the changes to a single domain controller by selecting one as the schema master, removing it from directory replication, and applying the LDIF file using the our favorite old school tool LDIFDE.EXE. Lastly, the domain controller is added back into replication to replicate the changes to the other domain controller and complete the changes. If you’ve been administering Windows AD you’ll know this has appeared recommended best practices for schema updates over the years.
Once the process is complete the console updates to show completion of the schema installation and the creation of the snapshot.
You didn’t think I was done with AWS Managed Microsoft AD yet did you? In this post I’m going to perform some tests to evaluate the protocols and ciphers suites available for LDAPS as well as checking out the managed Domain Controllers support for NTLMv1 and the cipher suites supported for Kerberos. I’ll be using the same testing mechanisms I used when for my series on Microsoft Azure Active Directory Domain Services.
For those of you who are new to the series, I’ve been performing a deep dive review of AWS Managed Microsoft AD which is Amazon’s answer to a managed Windows Active Directory service. In the first post I provided a high level overview of the service, in the second post I covered the setup of the service, the third post reviewed the directory structure, pre-configured security principals and group policies, and the delegated security model, and in the fourth entry I delved into how Amazon has managed to delegate configuration of LDAPS and the requirements that pop up due to their design choices. I highly recommend you review those posts as well as my series on Microsoft Azure AD Domain Services if you’d like to compare the two services.
I’ve made a modification to my lab and have added another server named SERVER02 which will be running Linux. The updated Visio looks like this.
Server01 has been configured with the Windows Remote Server Administration Tools (RSAT) for Active Directory as well as holding the Active Directory Certificate Services (AD CS) role and being configured as a root Enterprise CA. I’ve also done all the necessary configuration to distribute the certificates to the managed domain controllers and have successfully tested LDAPS. Server02 will be used to test SSLv3 and NTLM. I’ve modified the instance to use the domain controllers as DNS servers by overriding DHCP settings as outlined in this article.
The first thing I’m going to do is test to see if SSLv3 has been disabled on the managed domain controllers. Recall that the managed Domain Controllers are running Windows Server 2012 R2 which has SSLv3 enabled by default. It can be disabled by modifying the registry as documented here. Believe it or not you can connect to the managed domain controllers registry via a remote registry connection. Checking the registry location shows that the SSLv3 node hasn’t been created which is indicative of SSLv3 still being enabled.
To be sure I checked it using the same method that I used in my Azure AD Domain Services post which is essentially compiling another version of openssh that supports SSLv3. After the customized version was installed and I queried the Domain Controller over port 636 which you can see in the screenshot below that SSLv3 is still enabled. Suffice to say this surprised me considering what I had seen so far in regards to the security of the service. This will be a show stopper for some organizations in adopting the service especially since it isn’t configurable by the customer that I observed.
So SSLv3 is enabled and presents a risk. Have the cipher suites been hardened? For this I’ll again use a tool developed by Thomas Pornin. The options I’m using perform an exhaustive search across the typically offered cipher suites, space the connections out by 1 second, and start with a minimum of sslv3.
The results are what I expected and mimic the results I saw when testing Azure AD Domain Services, minus the support for SSLv3 which Microsoft has disabled in their managed offering. The supported cipher suites look to be the out of the box defaults for Server 2012 R2 and include RC4 and 3DES which are ciphers with known vulnerabilities. The inability to disallow the ciphers might again be a show stopper for organizations with strict security requirements.
The Kerberos protocol is a critical component of Windows Active Directory providing the glue to hold the service together including (but in no way exhaustive) being behind the users authentication to a domain-joined machine, the single sign-on experience, and the ability to form trusts with other forests. Given the importance of the protocol, it’s important to ensure its backed by strong ciphers. The ciphers supported by a Windows Active Directory are configurable and can be checked by looking at the msDS-SupportedEncryptionTypes attribute of a domain controller object.
I next pulled up a domain controller object in ADUC and reviewed the attribute. The attribute on the managed domain controllers has a value of 28, which is the default for Windows Server 2012 R2. The value translates to support of the following cipher suites:
These are the same cipher suites supported by Microsoft’s Azure AD Domain Services service. In this case both vendors have left the configuration to the defaults.
Lastly, to emulate my testing Azure AD Domain Services, I tested 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. Sadly there are a large number of applications and devices in use in enterprises which still require NTLMv1.
To test the AWS managed domain controllers I’m going to use Samba’s smbclient package on SERVER02. I’ll use the client to connect to the domain controller’s share from SERVER02 using NTLM. I first installed the smbclient package by running:
yum install samba-client.
The client enforces 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.
In order to see whether or not the client was using NTLMv1 when connecting to the domain controllers, I started a packet capture using tcpdump before initiating a connection with the smbclient.
I then transferred the packet capture over to my Windows box with WinSCP, 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.
So what can we take from the findings of this analysis?
I’d really like to see Amazon address the support for SSLv3 as soon as possible. There is no reason I can see why that shouldn’t be shut off by default. Similar to my requests to Microsoft, I’d like to see Amazon allow the supported cipher suites to be configurable via the AWS Management Console. These two changes would save organizations with strict security requirements, such as those in the public sector, to utilize the services without introducing significant risk (and audit headaches).
In my next post I’ll demonstrate how the service can be leveraged to provide Windows Active Directory service to on-premises machines or machines in another public cloud as well as exploring how to create a forest trust with the service.
See you next post!
Welcome back my fellow geeks!
Today I’m going to interrupt the series on AWS Managed Microsoft AD For the past few weeks, in between writing the entries for the recent deep dive series, I’ve been preparing for the AWS Cloud Practitioner exam. I thought it would be helpful to share my experience prepping for and passing the exam.
If you’re not familiar with the AWS Certificated Cloud Practitioner exam, it’s very much an introductory exam into the Amazon Web Services’ overarching architecture and products. Amazon’s intended audience for the certification are your C-levels, sales people, and technical people who are new to the AWS stack and potentially cloud in general. It’s very much an inch deep and mile wide. For those of you who have passed your CISSP, the experience studying for it similar (although greatly scaled down content-wise) in that you need to be able to navigate the shallow end of many pools.
Some of you may be asking yourselves why I invested my time in getting an introductory certificate rather than just going for the AWS Certified Solutions Architect – Associate. The reason is my personal belief that establishing a solid foundation in a technology or product is a must. I’ve encountered too many IT professionals with a decade more of experience and a hundred certificates to their name who can’t explain the basics of the OSI model or the difference in process between digitally signing something versus encrypting it. The sign of a stellar IT professional is one who can start at the business justification for an application and walk you right down through the stack to speak to the technology standards being leveraged within the application to deliver its value. This importance in foundation is one reason I recommend every new engineer start out by taking the CompTIA A+, Network+, and Security+ exams. You won’t find exams out there that better focus on foundational concepts than CompTIA exams.
The other selling point of this exam to me was the audience it’s intended for. Who wouldn’t want to know the contents and messaging in an exam intended for the C-level? Nothing is more effective influencing the C-level than speaking the language they’re familiar with and pushing the messaging you know they’ve been exposed to.
Let me step off this soapbox and get back to my experience with the exam. 🙂
As I mentioned above I spent about two weeks preparing for the exam. My experience with the AWS stack was pretty minimal prior to that restricted to experience for my prior blogs on Azure AD and AWS integration for SSO and provisioning and Microsoft Cloud App Security integration with AWS. As you can tell from the blog, I’ve done a fair amount of public cloud solutions over the past few years, just very minimally AWS. The experience in other public cloud solutions such as Microsoft Azure and Google Cloud Platform (GCP) proved hugely helpful because the core offerings are leveraging similar modern concepts (i.e. all selling computer, network, and storage). Additionally, the experiences I’ve had over my career with lots of different infrastructure gave me the core foundation I needed to get up and running. The biggest challenge for me was really learning the names of all the different offerings, their use cases, and their capabilities that set them apart from the other vendors.
For studying materials I followed most of the recommendations from Amazon which included reviews of a number of whitepapers. I had started the official Amazon Cloud Practitioner Essentials course (which is free by the way) but didn’t find the instructors engaging enough to keep my attention. I ended up purchasing a monthly subscription to courses offered by A Cloud Guru which were absolutely stellar and engaging at a very affordable monthly price (something like $29/month). In addition to the courses I read each of the recommended whitepapers (ended reading a bunch of others as well) a few times each taking notes of key concepts and terminology. While I was studying for this exam, I also was working on my AWS deep dive which helped to reinforce the concepts by actually building out the services for my own use.
I spent a lot of time diving into the rabbit whole of products I found really interesting (RedShift) as well as reading up on concepts I’m weaker on (big data analytics, modern nosql databases, etc). That rabbit hole consisted of reading blogs, Wikipedia, and standards to better understand the technical concepts. Anything I felt would be worthwhile I captured in my notes. Once I had a good 15-20 pages of notes (sorry all paper this time around), I grabbed the key concepts I wanted to focus on and created flash cards. I studying the deck of 200 or so flash cards each night as well as re-reading sections of the whitepapers I wanted to familiarize myself with.
For practice exams I used the practice questions Amazon provides as well as the quizzes from A Cloud Guru. I found the questions on the actual exam more challenging, but the practice question and quizzes were helpful to getting into the right mindset. The A Cloud Guru courses probably covered a good 85-90% of the material, but I wouldn’t recommend using it was a sole source of study, you need to read those whitepapers multiple times over. You also need to do some serious hands on because some of the questions do ask you very basic questions about how you do things in the AWS Management Console.
Overall it was a well done exam. I learned a bunch about the AWS product offerings, the capabilities that set AWS apart from the rest of the industry, and gained a ton of good insight into general cloud architecture and design from the whitepapers (which are really well done). I’d highly recommend the exam to anyone who has anything to do with the cloud, whether you’re using AWS or not. You’ll gain some great insight into cloud architecture best practices as well seeing modern technology concepts put in action.
I’ll be back with the next entry in my AWS Managed Microsoft AD series later this week. Have a great week and thanks for reading!
I’m back again with another entry in my deep dive into AWS Managed Microsoft Active Directory (AD). So far I’ve provided an overview of the service, covered how to configure the service, and analyzed the Active Directory default configuration such as the directory structure, security principals, password policies, and group policy setup by Amazon for new instances. In this post I’m going to look at the setup of LDAPS and how Amazon supports configuration of it in the delegated model they’ve setup for the service.
Those of you that have supported a Windows AD environment will be quite familiar with the wonders and sometimes pain of the Lightweight Directory Access Protocol (LDAP). Prior to the modern directories such as AWS Cloud Directory, Azure Active Directory the LDAP protocol served critical roles by providing both authentication and a method of which to work with data stored in directory data stores such as Windows AD. For better or worse the protocol is still relevant today when working with Windows AD for both of the above capabilities (less for authentication these days if you stay away from backwards-thinking vendors). LDAP servers listen on port 389 and 636 with 389 maintaining traffic in the clear (although there are exceptions where data is encrypted in transit such as Microsoft’s usage of Kerberos encryption or the use of StartTLS (credit to my friend Chris Jasset for catching my omission of StartTLS)) and 636 (LDAPS) providing encryption in transit via an SSL tunnel (hopefully not anymore) or a TLS tunnel.
Windows AD maintains that pattern and serves up the content of its data store over LDAP over ports 389 and 636 and additionally ports 3268 and 3269 for global catalog queries. In the assume breach days we’re living in, we as security professionals want to protect our data as it flows over the network which means we’ll more often than not (exceptions are again Kerberos encryption usage mentioned above) be using LDAPS over ports 636 or 3269. To provide that secure tunnel the domain controllers will need to be setup with a digital certificate issued by a trusted certificate authority (CA). Domain Controllers have unique requirements for the certificates they use. If you’re using Active Directory Certificate Services (AD CS) Microsoft takes care of providing the certificate template for you.
So how do you provision a certificate to a Domain Controller’s certificate store when you don’t have administrative privileges such as the case for a managed service like AWS Managed Active Directory? For Microsoft Azure Active Directory Domain Services (AAD DS) the public certificate and private key are uploaded via a web page in the Azure Portal which is a solid way of doing it. Amazon went in a different and instead takes advantage of certificate autoenrollment. If you’re not familiar with autoenrollment take a read through this blog. In short, it’s an automated way to distribute certificates and eliminate some of the overheard of manually going through the typical certificate lifecycle which may contain manual steps.
If we bounce back to the member server in my managed domain, open the Group Policy Management Console (GPMC), and navigate to the settings tab of the AWS Managed Active Directory Policy we see that autoenrollment has been enabled on the domain controllers. This setting explains why Amazon requires a member server joined to the managed domain be configured running AD CS. Once the AD CS instance is setup, the CA has been configured either to as a root or subordinate CA, and a proper template is enabled for autoenrollment, the domain controllers will request the appropriate certificate and will begin using it for LDAPS.
If you’ve ever worked with AD CS you may be asking yourself how you’ll be able to install AD CS in a domain where you aren’t a domain administrator when the Microsoft documentation specifically states you need to be a member of the Enterprise Admins and root domains Domain Admins group. Well folks that is where the AWS Delegated Enterprise Certificate Authority Administrators group comes into play. Amazon has modified the forest to delegate the appropriate permissions to install AD CS in a domain environment. If we navigate to the CN=Public Key Services, CN=Services, CN=Configuration using ADSIEdit and view the Security for the container we see this group has been granted full permissions over the node allowing the necessary objects to be populated underneath it.
I found it interesting that in the instructions provided by Amazon for enabling LDAPS the instructions state the Domain Controller certificate template needs to modified to remove the Client Authentication EKU. I’d be interested in knowing the reason for modifying the Domain Controller certificate. If I had to guess it’s to prevent the domain controller from using the certificate outside of LDAPS such as for mutual authentication during smart card logon. Notice that from this article domain controllers only require the Server Authentication EKU when a certificate is only used to secure LDAPS.
I’ve gone ahead and installed AD CS on SERVER01 as an Enterprise root CA and thanks to the delegation model, the CA is provisioned with all the necessary goodness in CN=Public Key Services. I also created the new certificate template following the instructions from Amazon. The last step is to configure the traffic flow such that the managed domain controllers can contact the CA to request a certificate. The Amazon instructions actually have a typo in them. On Step 4 it instructs you to modify the security group for your CA and to create a new inbound rule allowing all traffic from the source of your CA’s AWS Security group. The correct security group is actually the security group automatically configured by Amazon that is associated with the managed Active Directory instance.
At this point you’ll need to wait a few hours for the managed domain controllers to detect the new certificates available for autoenrollment. Mine actually only took about an hour to roll the certificates out.
To test the service I opened LDP.EXE and established a secure session over port 636 and all worked as expected.
Since I’m a bit OCD I also pulled the certificate using openssl to validate it’s been issued by my CA. As seen in the screenshot below the certificate was issued by the geekintheweeds-CA which is the CA I setup earlier.
Beyond the instructions Amazon provides, you’ll also want to give some thought as to how you’re going to handle revocation checks. Keep in mind that by default AD CS stores revocation information in AD. If you have applications configured to check for revocation remember to ensure those apps can communicate with the domain controllers over port 389 so design your security groups with this in mind.
Well folks that will wrap up this post. Now that LDAPS is configured, I’ll begin the tests looking at the protocols and ciphers supported when accessing LDAPS as well as examining the versions of NTLM supported and the encryption algorithms supported with Kerberos.
See you next post!