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Certificate Services (AD-CS) ​

Theory ​

AD CS is Microsoft’s PKI implementation that provides everything from encrypting file systems, to digital signatures, to user authentication (a large focus of our research), and more. While AD CS is not installed by default for Active Directory environments, from our experience in enterprise environments it is widely deployed, and the security ramifications of misconfigured certificate service instances are enormous. (specterops.io)

In their research papers, Will Schroeder and Lee Christensen shared their research on AD CS and identified multiple theft, escalation and persistence vectors.

Practice ​

Escalation techniques ​

Terminology ​

  • PKI (Public Key Infrastructure) — a system to manage certificates/public key encryption
  • AD CS (Active Directory Certificate Services) — Microsoft’s PKI implementation
  • CA (Certificate Authority) — PKI server that issues certificates
  • Enterprise CA — CA integrated with AD (as opposed to a standalone CA), offers certificate templates
  • Certificate Template — a collection of settings and policies that defines the contents of a certificate issued by an enterprise CA
  • CSR (Certificate Signing Request) — a message sent to a CA to request a signed certificate
  • EKU (Extended/Enhanced Key Usage) — one or more object identifiers (OIDs) that define how a certificate can be used
  • Application Policy — this does the same thing as EKUs, but with a few more options. Specific to Windows environments

(specterops.io)

Recon ​

While AD CS offers attackers a wide range of exploitation and persistence scenarios, this set of services is not always installed, and when it is, it is a requirement to identify its different parts in the domain.

Cert Publishers ​

An initial indicator is the "Cert Publishers" built-in group whose members usually are the servers where AD CS is installed (i.e. PKI/CA).

  • From UNIX-like systems: rpc net group members "Cert Publishers" -U "DOMAIN"/"User"%"Password" -S "DomainController"
  • From Windows systems: net group "Cert Publishers" /domain

pKIEnrollmentService objects ​

Alternatively, information like the PKI's CA and DNS names can be gathered through LDAP.

netexec's adcs module (Python) can be used to find PKI enrollment services in AD.

bash
netexec ldap 'domaincontroller' -d 'domain' -u 'user' -p 'password' -M adcs

Attack paths ​

Certipy (Python) and Certify (C#) can also identify the PKI enrollment services and potential attack paths.

From UNIX-like systems, the Certipy (Python) tool can be used to operate multiple attacks and enumeration operations.

python
# enumerate and save text, json and bloodhound (original) outputs
certipy find -u 'user@domain.local' -p 'password' -dc-ip 'DC_IP' -old-bloodhound

# quickly spot vulnerable elements
certipy find -u 'user@domain.local' -p 'password' -dc-ip 'DC_IP' -vulnerable -stdout

Certipy also supports BloodHound. With the -old-bloodhound option, the data will be exported for the original version of BloodHound. With the -bloodhound option, the data will be exported for the modified version of BloodHound, forked by Certipy's author (default output when no flag is set).

The tool also supports multiple output types (text, json, stdout).

By default, Certipy uses LDAPS, which is not always supported by the domain controllers. The -scheme flag can be used to set whether to use LDAP or LDAPS.

Abuse ​

The different domain escalation scenarios are detailed in the following parts.

Resources ​

https://posts.specterops.io/certified-pre-owned-d95910965cd2

https://www.riskinsight-wavestone.com/en/2021/06/microsoft-adcs-abusing-pki-in-active-directory-environment

https://http418infosec.com/ad-cs-what-can-be-misconfigured

https://http418infosec.com/ad-cs-the-certified-pre-owned-attacks

https://research.ifcr.dk/certipy-2-0-bloodhound-new-escalations-shadow-credentials-golden-certificates-and-more-34d1c26f0dc6

https://trustedsec.com/blog/ekuwu-not-just-another-ad-cs-esc

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