Active Directory - Page 4 - Uwe Gradenegger

Description of certificate template generations

Below is a description of the different generations of certificate templates (schema versions) and the innovations introduced with them.

Requesting a certificate fails with the error message "You cannot request a certificate at this time because no certificate types are available."

Assume the following scenario:

You try to apply for a certificate from an Active Directory-integrated certification authority (Enterprise Certification Authority).
To do this, use the Microsoft Management Console (MMC), either for the logged-in user (certmgr.msc) or for the computer (certlm.msc).
The logged-in user also has the necessary permissions to request certificates from the certificate template in question (enroll).
You don't get any certificate templates to choose from, even though they are correctly published on the certificate authorities.
There is also no "Show hidden templates" option. This usually appears at the bottom left of the dialog.
The following error message is displayed:

Certificate types are not available. You cannot request a certificate at this time because no certificate types are available. If you need a certificate, contact your administrator.

Publishing a certificate template on a CA fails with error message "The template information on the CA cannot be modified at this time. This is most likely because the CA service is not running or there are replication delays. Access is denied. 0x80070005 (WIN32: 5 ERROR_ACCESS_DENIED)".

Assume the following scenario:

An administrator publishes a certificate template on a certificate authority.
The operation fails with the following error message:

The template information on the CA cannot be modified at this time. This is most likely because the CA service is not running or there are replication delays. Access is denied. 0x80070005 (WIN32: 5 ERROR_ACCESS_DENIED)

Use Authentication Mechanism Assurance (AMA) to secure administrative account logins.

Authentication Mechanism Assurance (AMA) is a feature designed to ensure that a user is a member of a security group only if they can be shown to have logged in using a strong authentication method (i.e., a smart card). If the user logs in via username and password instead, he or she will not have access to the requested resources.

Originally intended for access to file servers, however, AMA can also be used (with some restrictions) for administrative logon. Thus, for example, it would be conceivable for a user to be unprivileged when logging in with a username and password, and to have administrative rights when logging in with a certificate.

Certificate request basics via Certificate Enrollment Web Services (CEP, CES)

With Windows Server 2008 R2 and Windows 7, a new functionality for certificate enrollment has been introduced: The Certificate Enrollment Web Services, which are mapped by two server roles:

Certificate Enrollment Policy Web Service (CEP)
Certificate Enrollment Web Services (CES)

The following is a description of the background to these roles, how they work, and the possible deployment scenarios.

Basics of manual and automatic certificate requests via Lightweight Directory Access Protocol (LDAP) and Remote Procedure Call / Distributed Common Object Model (RPC/DCOM) with the MS-WCCE protocol

The following describes the process that runs in the background when certificates are requested manually or automatically in order to achieve the highest possible level of automation.

Manually running the autoenrollment process

By default, all domain members automatically replicate the Public Key Services object he Active Directory forest through the autoenrollment process. The triggers for this are:

When the user logs in (for computers, when the computer account logs in, i.e. at system startup).
By timer every 8 hours.
When updating group policies, assuming there has been a change.

If you do not want to wait for the autoenrollment to be triggered automatically, you can start it manually. The different ways to run the autoenrollment process are described below.

Associate a universal security group with an Object Identifier (OID) in the Active Directory directory service (Authentication Mechanism Assurance).

Authentication Mechanism Assurance (AMA) provides the ability to tie membership in a security group to enrollment with a smart card certificate containing a specific Object Identifier (OID).

If the user does not log in with the smartcard certificate, but with user name and password, he is also not a member of the security group.

The following describes how to establish the connection between the certificate and the security group.

Configuring a Certificate Template for Authentication Mechanism Assurance (AMA)

Authentication Mechanism Assurance (AMA) provides the ability to tie membership in a security group to enrollment with a smart card certificate containing a specific Object Identifier (OID).

If the user does not log in with the smartcard certificate, but with user name and password, he is also not a member of the security group.

The following describes how to generate a certificate template for use with Authentication Mechanism Assurance.

Domain Controller Certificate Templates and Smartcard Logon

In order for domain controllers to process smart card logins, they need certificates that provide this function.

(Re-)Installing the Microsoft Standard Certificate Templates

There may be cases where it is necessary to install the standard Microsoft certificate templates before installing the first Active Directory integrated certificate authority (Enterprise Certification Authority), or to reinstall the templates, for example because they have been corrupted or otherwise modified.

Editing the NTAuthCertificates object in Active Directory

In the default configuration, all certification authority certificates of Active Directory integrated certification authorities (Enterprise Certification Authority) are located in an object of type CertificationAuthority named NTAuthCertificates within the Configuration Partition of the Active Directory forest.

Attack vector on Active Directory directory service via smartcard logon mechanism

In simple terms, public key cryptography can be reduced to the assumption that the private part of each key pair is known only to its owner.

A certification authority is responsible for the correct identification of users, computers or resources. Its issued certificates are therefore granted a trust status because all participants assume that their private key is known only to it.

If an attacker succeeds in gaining knowledge of a certification authority's private key, or at least Perform signatures using the private key, the integrity of the certification authority is no longer guaranteed.

Installing the Network Device Enrollment Service (NDES) without Enterprise Administrator permissions

Assume the following scenario:

One installs a Network Device Enrollment Service (NDES) server.
The role configuration fails with the following error message:

Insufficient access rights to perform this operation. 0x80072098 (WIN32: 8344 ERROR_DS_INSUFF_ACCESS_RIGHTS

Typically, the NDES roll configuration requires, that the installing user is a member of the Enterprise Admins group. However, this is not technically necessary and contradicts Microsoft's security hardening recommendations, since NDES is not (necessarily) a system that is assigned to the highest security layer (Tier-0).

Below is a way to configure the NDES role even without the required permissions.

Publishing a certificate revocation list (CRL) fails with the error message "Insufficient access rights to perform the operation. 0x80072098 (WIN32: 8344 ERROR_DS_INSUFF_ACCESS_RIGHTS)".

Assume the following scenario:

An attempt is made to publish a new certificate revocation list (CRL) on a certification authority
The certificate authority is configured to publish the certificate revocation lists to Active Directory (LDAP CDP).
Publishing the certificate revocation list fails with the following error message:

Insufficient access rights to perform the operation. 0x80072098 (WIN32: 8344 ERROR_DS_INSUFF_ACCESS_RIGHTS)