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Metasploit Documentation

What is AD CS?

Active Directory Certificate Services, also known as AD CS, is an Active Directory tool for letting administrators issue and manage public key certificates that can be used to connect to various services and principals on the domain. It is often used to provide certificates that can be used in place of credentials for logging into a network, or to provide certificates that can be used to sign and verify the authenticity of data.

The main guarantees that AD CS aims to provide are:

  • Confidentiality via encryption
  • Integrity via digital signatures
  • Authentication by associating certificate keys with computers, users, or device accounts on a computer network.

Given that AD CS often holds highly sensitive keys and access credentials for a corporate network, this makes it a prime target for attackers.

Required Ports for AD CS

Active Directory requires the following TCP ports be open on all domain controllers, which heavily overlaps with the ports required for AD CS:

  • TCP/UDP port 53: DNS
  • TCP/UDP port 88: Kerberos authentication
  • TCP/UDP port 135: RPC
  • TCP/UDP port 137-138: NetBIOS
  • TCP/UDP port 389: LDAP
  • TCP/UDP port 445: SMB
  • TCP/UDP port 464: Kerberos password change
  • TCP/UDP port 636: LDAP SSL
  • TCP/UDP port 3268-3269: Global catalog

AD CS additionally has the following requirements for Certificate Authorities:

  • TCP random port above 1023: RPC dynamic port allocation

The following ports are optional depending on services used, and tend to apply to Certificate Enrollment Web Services:

  • TCP port 80: HTTP
  • TCP port 443: HTTPS
  • TCP port 445: SMB

If using Active Directory Federation Services (ADFS) for single sign on the following ports are also required:

  • TCP port 80: HTTP
  • TCP port 443: HTTPS
  • TCP port 49443: ADFS

Core Concepts

Microsoft provides a very useful training module that covers the fundamentals of AD CS and as well as examples which cover the management of certificate enrollment, certificate revocation and certificate trusts.

Setting up A Vulnerable AD CS Server

The following steps assume that you have installed an AD CS on either a new or existing domain controller.

Installing AD CS

  1. Open the Server Manager
  2. Select Add roles and features
  3. Select “Active Directory Certificate Services” under the “Server Roles” section
  4. When prompted add all of the features and management tools
  5. On the AD CS “Role Services” tab, leave the default selection of only “Certificate Authority”
  6. Completion the installation and reboot the server
  7. Reopen the Server Manager
  8. Go to the AD CS tab and where it says “Configuration Required”, hit “More” then “Configure Active Directory Certificate…”
  9. Select “Certificate Authority” in the Role Services tab
  10. Select “Enterprise CA” in the “Setup Type” tab (the user must be a Domain Administrator for this option to be available)
  11. Keep all of the default settings, noting the value of the “Common name for this CA” on the “CA Name” tab (this value corresponds to the CA datastore option)
  12. Accept the rest of the default settings and complete the configuration

Setting up a ESC1 Vulnerable Certificate Template

  1. Open up the run prompt and type in certsrv.
  2. In the window that appears you should see your list of certification authorities under Certification Authority (Local). Right click on the folder in the drop down marked Certificate Templates and then click Manage.
  3. Scroll down to the User certificate. Right click on it and select Duplicate Template.
  4. From here you can refer to the following Active-Directory-Certificate-Services-abuse documentation for screenshots.
  5. Select the General tab and rename this to something meaningful like ESC1-Template, then click the Apply button.
  6. In the Subject Name tab, select Supply in the request and click Ok on the security warning that appears. Then click the Apply button.
  7. Scroll to the Extensions tab and under Application Policies ensure that Client Authentication, Server Authentication, KDC Authentication, or Smart Card Logon is listed. Then click the Apply button.
  8. Under the Security tab make sure that Domain Users group listed and the Enroll permissions is marked as allowed for this group.
  9. Under Issuance Requirements tab, ensure that under Require the following for enrollment that the CA certificate manager approval box is unticked, as is the This number of authorized signatures box.
  10. Click Apply and then Ok
  11. Go back to the certsrv screen and right click on the Certificate Templates folder. Then click New followed by Certificate Template to Issue.
  12. Scroll down and select the ESC1-Template certificate, or whatever you named the ESC1 template you created, and select OK. The certificate should now be available to be issued by the CA server.

Setting up a ESC2 Vulnerable Certificate Template

  1. Open up certsrv
  2. Scroll down to Certificate Templates folder, right click on it and select Manage.
  3. Find the ESC1 certificate template you created earlier and right click on that, then select Duplicate Template.
  4. Select the General tab, and then name the template ESC2-Template. Then click Apply.
  5. Go to the Subject Name tab and select Build from this Active Directory Information and select Fully distinguished name under the Subject Name Format. The main idea of setting this option is to prevent being able to supply the subject name in the request as this is more what makes the certificate vulnerable to ESC1. The specific options here I don’t think will matter so much so long as the Supply in the request option isn’t ticked. Then click Apply.
  6. Go the to Extensions tab and click on Application Policies. Then click on Edit.
  7. Delete all the existing application policies by clicking on them one by one and clicking the Remove button.
  8. Click the Add button and select Any Purpose from the list that appears. Then click the OK button.
  9. Click the Apply button, and then OK. The certificate should now be created.
  10. Go back to the certsrv screen and right click on the Certificate Templates folder. Then click New followed by Certificate Template to Issue.
  11. Scroll down and select the ESC2-Template certificate, or whatever you named the ESC2 template you created, and select OK. The certificate should now be available to be issued by the CA server.

Setting up a ESC3 Template 1 Vulnerable Certificate Template

  1. Follow the instructions above to duplicate the ESC2 template and name it ESC3-Template1, then click Apply.
  2. Go to the Extensions tab, click the Application Policies entry, click the Edit button, and remove the Any Purpose policy and replace it with Certificate Request Agent, then click OK.
  3. Click Apply.
  4. Go to Issuance Requirements tab and double check that both CA certificate manager approval and This number of authorized signatures are unchecked.
  5. Click Apply if any changes were made or the button is not grey’d out, then click OK to create the certificate.
  6. Go back to the certsrv screen and right click on the Certificate Templates folder. Then click New followed by Certificate Template to Issue.
  7. Scroll down and select the ESC3-Template1 certificate, or whatever you named the ESC3 template number 1 template you just created, and select OK. The certificate should now be available to be issued by the CA server.

Setting up a ESC3 Template 2 Vulnerable Certificate Template

  1. Follow the instructions above to duplicate the ESC2 template and name it ESC3-Template2, then click Apply.
  2. Go to the Extensions tab, click the Application Policies entry, click the Edit button, and remove the Any Purpose policy and replace it with Client Authentication, then click OK.
  3. Click Apply.
  4. Go to Issuance Requirements tab and double check that both CA certificate manager approval is unchecked.
  5. Check the This number of authorized signatures checkbox and ensure the value specified is 1, and that the Policy type required in signature is set to Application Policy, and that the Application policy value is Certificate Request Agent.
  6. Click Apply and then click OK to issue the certificate.
  7. Go back to the certsrv screen and right click on the Certificate Templates folder. Then click New followed by Certificate Template to Issue.
  8. Scroll down and select the ESC3-Template2 certificate, or whatever you named the ESC3 template number 2 template you just created, and select OK. The certificate should now be available to be issued by the CA server.