Tag: PSCertificateEnrollment

With the May 2026 security update, Microsoft has added support for the ML-DSA algorithm in Active Directory Certificate Services.

In their documentation, they do write that NDES is not compatible with ML-DSA :

You can enroll ML-DSA certificates through the Certificates Microsoft Management Console (MMC) snap-in and certreq.exe. Enrollment through the Network Device Enrollment Service (NDES) isn't currently available.

But that's not entirely true…

Continue reading "Requesting Certificates with ML-DSA-Based Keys Through the Network Device Enrollment Service (NDES)"

Dirk-jan Mollema recently presented an attack that can be used to obtain a certificate for highly privileged accounts via Intune . This can then be used to compromise the entire Active Directory environment.

The attack is similar in its basic features to what I have already described in the article "From Zero to Enterprise Administrator through Network Device Enrollment Service (NDES) - and What to Do About It " and in the article "Attack vector on Active Directory directory service via smart card logon mechanism " (generally also known as ESC1 ).

What is new, however, is to utilize the Mobile Device Management (MDM) system - in this case Microsoft Intune - accordingly.

What is not new, however, is what can be done with the TameMyCerts Policy Module for Active Directory Certificate Services to drastically reduce the attack surface...

Continue reading "Attack on the Active Directory via Microsoft Intune - and how it can be contained with TameMyCerts"

Like any software Microsoft Active Directory Certificate Services are also subject to certain limits imposed by their design.

What is not so obvious is the question of how many subject alternative names (SAN) can be issued with the Microsoft certification authority.

The IETF RFC 5280 describes the structure for Subject Alternative Names as follows:

SubjectAltName ::= GeneralNames

Continue reading "How many Subject Alternative Names (SAN) do the Active Directory Certificate Services support?"

The purposes for which a digital certificate may be used are controlled via the "Key Usage" and "Extended Key Usage" certificate extensions. The "Extended Key Usage" certificate extension contains the extended key usages for which the certificate may be used.

However, certificates issued by a Microsoft certification authority contain another certificate extension called "Application Policies", which also contains a list very similar to the Extended Key Usages extension.

Justin Bollinger from TrustedSec has found out that with offline certificate requests against schema version 1 certificate templates it is possible (similar to the Security Identifier extension ) to include arbitrary Application Policies in the certificate request, which are transferred unchanged to the issued certificate and can then be used to attack the Active Directory forest. The attack was named ESC15.

Continue reading "New ESC15 vulnerability discovered in Active Directory Certificate Services - easy-to-implement countermeasures"

Usually, the encoding of characters and strings in certificates is not a topic of great interest to the users of a PKI. However, there are cases where the default settings of the certification authority do not provide the desired results.

Continue reading "Character encoding in the Subject Distinguished Name of certificate requests and issued certificates"

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 Enrollment Service (NDES). How exactly this is implemented and how this may change the application behavior is explained below.

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

Assume the following scenario:

• A certificate template is configured to use elliptic curve based keys (e.g. ECDSA_P256).
• As a result, a minimum key length of 256 bits is configured.
• Nevertheless, certificate requests that use other ECC curves or RSA-based keys are also signed.

Continue reading "The key algorithm of certificate requests is not checked by the certification authority's policy module"

In the following, I would like to present a highly dangerous PKI configuration, perhaps not necessarily known to the general public, which can probably be encountered quite frequently in this way in corporate networks.

I show how, by exploiting various unfortunate circumstances in the Windows PKI, it is possible to elevate privileges from mere network access to complete Active Directory takeover.

The initial point of attack in this example is the Network Device Enrollment Service (NDES).

Continue reading "From Zero to Enterprise Administrator through Network Device Enrollment Service (NDES) - and What to Do About It"

The attack on the MD5 signature algorithm demonstrated in late 2008 could only be used to create a usable forged certification authority certificate because the attacked certification authority had not configured a path length constraint.

The path length constraint is described in RFC 5280 . The idea behind this is that the maximum depth of the certification authority hierarchy is stored in the "Basic Constraints" extension of a certification authority certificate.

Continue reading "Basics: Path Length Constraint"

There are cases in which you cannot or do not want to obtain web server certificates directly from a certification authority in your own Active Directory forest via the Microsoft Management Console, for example if the system in question is not a domain member.

In this case, the use of certificate templates is not possible, and one must manually create a Certificate Signing Request (CSR).

Continue reading "Manually requesting a web server certificate"

Since Windows 8, it is possible to protect private keys for certificates with a Trusted Platform Module (TPM), if one is available . This makes the key non-exportable - even with tools like mimikatz.

However, it is not obvious at first glance that it cannot be guaranteed that a TPM is really used. Admittedly, no request via the Microsoft Management Console or autoenrollment will be possible if the computer does not have a TPM.

However, the configuration in the certificate template is merely a default setting for the client. The certification authority will not explicitly check whether a trusted platform module has actually been used when a request is made.

Thus - if the certificate request is done away from the MMC - arbitrary parameters can be used for the private key.

Continue reading "Requesting a certificate protected by a Trusted Platform Module (TPM) - without owning a TPM"

Time and again in discussions about the security of a certification authority, it comes up that abuse of the certification authority could be contained by its security settings.

However, the fact that the integrity of a certification authority is directly tied to its key material and can therefore also be compromised through it is not obvious at first glance.

One has to think of the certification authority software as a kind of management around the key material. For example, the software provides an online interface for certificate enrollment , takes care of the authentication of the enrollees, the automated execution of signature operations (issuing certificates and certificate revocation lists ) and their logging (certification authority database , audit log , event log ).

However, signature operations require nothing more than the private key of the certification authority. The following example shows how an attacker, given access to the certification authority's private key, can generate and issue certificates without the certification authority software and its security mechanisms noticing.

With such a certificate, it would in the worst case even be possible to take over the Active Directory forest undetected .

Continue reading "Signing certificates bypassing the certification authority"

If you want to equip Windows systems with certificates that do not have the option of communicating directly with an Active Directory-integrated certification authority, or that are not even in the same Active Directory forest, the only option in most cases is to install certificates manually.

Since Windows 8.1 / Windows Server 2012 R2, however, there is an integrated client for the Simple Certificate Enrollment Protocol (SCEP) on board. On the server side, SCEP has been implemented in the Microsoft PKI via the Network Device Enrollment Service (NDES) since Windows Server 2003.

A particularly interesting feature of SCEP is that the protocol allows a certificate to be renewed by specifying an existing one. So what could be more obvious than to use this interface? What is still missing is a corresponding automation via Windows PowerShell.

Continue reading "Requesting a Certificate for Windows Systems Using the SCEP Protocol via the Network Device Enrollment Service (NDES) with Windows PowerShell"

The Network Device Enrollment Service (NDES) has the ability to authenticate with a previously issued certificate in order to request a certificate with the same content again. This is very convenient for renewal operations, as it eliminates the need to request a one-time password beforehand.

Continue reading "Authentication at the Network Device Enrollment Service (NDES) with an existing certificate (renewal mode)"

There are cases where you cannot or do not want to obtain domain controller certificates from a certification authority in your own Active Directory forest.

In this case, the use of certificate templates is not possible, and one must manually create a Certificate Signing Request (CSR).

Continue reading "Manually requesting a domain controller certificate"