May 2022 - Uwe Gradenegger

Basics: Authentication procedures for the Internet Information Services (IIS)

The Active Directory Certificate Services offer a number of web-based add-on interfaces (Network Device Registration Service (NDES), Certificate Enrollment Policy Web Service (CEP), Certificate Enrollment Web Service (CES), Certification Authority Web Enrollment (CAWE).

The Microsoft Internet Information Services (IIS) are thus almost indispensable for a Microsoft PKI. Each of the web-based interfaces (and also in-house developments) bring their own unique challenges in terms of authentication procedures and their implementation.

The following article should bring a little clarity to the topic.

Enabling Basic Authentication for the Network Device Enrollment Service (NDES)

If the Network Device Enrollment Service (NDES) is reinstalled (Preferably without Enterprise Administrator permissions), only the Windows-integrated authentication for the administration web page is activated at first. With this (via NT LAN Manager, NTLM) protocol, authentication via user name and password is also possible. However, not all client applications support this.

Likewise, a company might be willing to, Disable NTLM where possible and enforce Kerberos for login. Enforcing Kerberos removes the ability to log in to the Network Device Registration Service administration page via username and password (since this is done with NTLM credentials). However, Basic Authentication can be retrofitted to provide an option here again.

One way out of this dilemma can be Basic Authentication, the setup of which will be explained below.

Disabling NTLM and enforcing Kerberos at the Network Device Enrollment Service (NDES) administration web page.

Many companies pursue the strategy of (largely) disabling the NT LAN Manager (NTLM) authentication protocol in their networks.

This is also possible for the administration web page of the network device registration service (NDES). How exactly this is implemented and how this may change the application behavior is explained below.

Changes to Certificate Issuance and Certificate-Based Logon to Active Directory with the May 10, 2022 Patch for Windows Server (KB5014754)

With the May 10, 2022 patch, Microsoft is attempting to patch a vulnerability in the Active Directory in which the certificate-based enrollment (commonly known as PKINIT or also Smartcard Logon) to close.

The update changes both the behavior of the Certification Authority as well as the behavior of Active Directory when processing certificate-based logins.