During penetration tests and also for attackers searching the network for potential targets, insights into the configuration of the certification authority are highly interesting.
In addition to possible misconfigurations, attackers can obtain information about the policy module used on the certification authority.
Since the recently released version 1.7, the TameMyCerts Policy Module for Microsoft Active Directory Certificate Services supports Personal Identity Verification (PIV) attestation for YubiKeys.
A YubiKey is a compact security token that can be used, among other things, like a smart card for the secure storage and use of certificates and can therefore also be used for passwordless logon to Active Directory environments.
This cool function was developed by Oscar Virot and integrated into TameMyCerts. This makes it possible to provide cryptographic proof when issuing certificates and thus ensure that a key pair is actually generated with a YubiKey and secured by it and cannot be exported.
This can be particularly helpful in complying with the NIS2 directive if companies decide to use certificates as a second factor for logon with security-critical accounts in Active Directory.
Nowadays, it is essential to protect the authentication of devices on the company network and administrative interfaces. As a rule, digital certificates are used for this purpose.
Printers therefore also generally require digital certificates in order to be operated securely. From a certain number of devices, there is no getting around automatic certificate distribution.
Some printer manufacturers offer centralized management solutions for certificate distribution.
Unfortunately, it has been shown time and again that the secure handling of digital certificates requires a great deal of knowledge, experience and care, which is often not the case.
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.
Attacks on Microsoft certification authorities can be aimed at exploiting permissions on certificate templates. In many cases, certificate templates must be configured to grant the enrollee the right to request arbitrary identities. This can lead to the attacker taking over the identities of Active Directory accounts and subsequently to privilege escalation. Attacks of this type are known in the security scene as "ESC1 ".
With the supposedly good intention of making it possible to issue such certificate requests with a SAN, unfortunately far too many guides advise enabling the EDITF_ATTRIBUTESUBJECTALTNAME2 flag on the certification authority.
If this flag is enabled, a very large attack surface is offered, as any enrollee can now instruct the certification authority to issue certificates with any content. This type of attack is known in the security scene as ESC6 and ESC7 .
As the operator of a certification authority, you are (among other things) responsible for the identification of the enrollees and the confirmation of the requested identities . The fact that this task is carried out conscientiously and without error is the central pillar of the trust placed in the certification authority. Well-known companies have already failed at this task , even had to file for insolvency as a result of misissuances and/or were severely punished by the big players in the market.
In many cases, we as (Microsoft) PKI operators in companies (regardless of the associated quality) are able to delegate our task of uniquely identifying an enrollee to the Active Directory. In many cases, however, we unfortunately also have to instruct our certification authority(ies) to simply issue everything that is requested.
With the May 10, 2022 patch, Microsoft is attempting to close a vulnerability in Active Directory that affects certificate-based logon (commonly known as PKINIT or also smart card logon ).
The update changes both the behavior of the certification authority as well as the behavior of Active Directory when processing certificate-based logons.
The purposes for which a digital certificate may be used are controlled via the certificate extensions "Key Usage" and "Extended Key Usage".
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.
Continue reading "The "Application Policies" certificate extension"
Assume the following scenario:
Continue reading "New certificates are regularly requested via autoenrollment"
Assume the following scenario:
Unfortunately, far too many instructions are circulating online (the big players are not exempt from this either, not even Microsoft itself or the grand master Komar ), which fatally recommend setting the EDITF_ATTRIBUTESUBJECTALTNAME2 flag on the certification authority - supposedly so that one would be able to issue certificates with a Subject Alternative Name (SAN) extension for manually submitted certificate requests.
Unfortunately, this approach is not only unnecessary, it also has some unpleasant side effects, which in the worst case can help an attacker to take over the entire Active Directory forest.
Continue reading "Active Directory forest compromised by EDITF_ATTRIBUTESUBJECTALTNAME2 flag"