10 Microsoft CA Best Practices

Microsoft Certificate Authorities (CAs) are an important part of any organization’s security infrastructure. They are used to issue digital certificates that are used to authenticate users, devices, and applications.

In order to ensure that your Microsoft CA is secure and reliable, it is important to follow best practices. This article will discuss 10 best practices for managing and maintaining your Microsoft CA. We will cover topics such as certificate lifecycle management, certificate revocation, and security hardening. Following these best practices will help ensure that your Microsoft CA is secure and reliable.

1. Use a dedicated CA for issuing certificates

Using a dedicated CA for issuing certificates ensures that the certificate authority is not used for any other purpose. This helps to reduce the risk of an attacker gaining access to the CA and using it to issue malicious certificates. It also reduces the attack surface by limiting the number of services running on the server, which can help prevent attackers from exploiting vulnerabilities in those services. Finally, having a dedicated CA makes it easier to monitor and audit the system, as all activity related to the CA will be centralized.

2. Implement certificate revocation lists (CRLs)

CRLs are lists of certificates that have been revoked by the CA. This is important because it allows organizations to revoke a certificate if it has been compromised or stolen, and prevent any malicious actors from using it for nefarious purposes.

CRLs should be published regularly so that clients can check them when validating certificates. The frequency of publication depends on the organization’s security requirements, but generally speaking, CRLs should be published at least once per day. Additionally, CRLs should be stored in an accessible location, such as a web server, so that they can be easily accessed by clients.

3. Publish the CRL to Active Directory

When a client computer attempts to validate the authenticity of an SSL certificate, it will check the CRL (Certificate Revocation List) to make sure that the certificate is still valid. If the CRL isn’t published in Active Directory, then the client won’t be able to access the list and therefore won’t be able to verify the validity of the certificate. This can lead to security issues as malicious certificates could potentially be used without detection.

By publishing the CRL to Active Directory, you ensure that all clients have easy access to the most up-to-date version of the CRL, allowing them to quickly and easily verify the validity of any SSL certificate they encounter.

4. Issue short-lived certificates

Short-lived certificates are more secure than long-term ones because they reduce the window of opportunity for attackers to exploit them. If a certificate is compromised, it will only be valid for a short period of time before it expires and needs to be replaced. This makes it much harder for an attacker to use the certificate for malicious purposes.

Additionally, short-lived certificates can help ensure that your organization’s security posture remains up-to-date. By regularly issuing new certificates, you can make sure that any outdated or vulnerable certificates are quickly replaced with newer, more secure versions.

5. Set up an online responder

An online responder is a server that responds to requests for certificate status information. It’s an important part of the Certificate Authority (CA) infrastructure, as it helps ensure that certificates issued by the CA are valid and trusted.

The online responder should be set up in accordance with Microsoft’s guidelines, which include using secure protocols such as TLS 1.2 or higher, configuring the server to use strong encryption algorithms, and setting up appropriate access control lists. Additionally, the online responder should be regularly monitored and updated to ensure its security posture remains intact.

6. Configure OCSP stapling in IIS 8 and later

OCSP stapling is a security feature that helps protect against man-in-the-middle attacks. It works by having the web server (IIS) query the certificate authority’s OCSP responder for the current revocation status of its SSL/TLS certificates and then “stapling” this response to the TLS handshake. This allows clients to verify the validity of the certificate without needing to contact the CA directly, which can improve performance and reduce latency.

Configuring OCSP stapling in IIS 8 and later is relatively straightforward. All you need to do is enable the feature in the IIS Manager console, configure the OCSP responder URL, and restart the website. Once enabled, your site will be better protected from malicious actors attempting to intercept or modify traffic.

7. Enable Certificate Revocation List Distribution Point (CDP) extension checking

The CDP extension is a critical part of the certificate validation process. It contains information about where to find the Certificate Revocation List (CRL) that lists all revoked certificates issued by the CA. Without this, clients won’t be able to determine if a certificate has been revoked or not.

Enabling CDP extension checking ensures that clients are always up-to-date with the latest list of revoked certificates and can make sure they’re only using valid certificates. This helps protect against malicious actors who may try to use revoked certificates for nefarious purposes.

8. Disable autoenrollment of Domain Controller certificates

Autoenrollment of Domain Controller certificates can be a security risk because it allows any user with access to the domain controller to request and receive a certificate. This could potentially allow malicious users to gain access to sensitive information or resources on the network.

To prevent this, administrators should disable autoenrollment of Domain Controller certificates in their Microsoft CA environment. This will ensure that only authorized personnel are able to request and receive certificates from the Microsoft CA server.

9. Do not use self-signed certificates on domain controllers

Self-signed certificates are not trusted by other computers, so they cannot be used to authenticate domain controllers. This means that if a malicious user were to gain access to the self-signed certificate, they could potentially impersonate the domain controller and gain access to sensitive data.

Using an enterprise CA instead of a self-signed certificate ensures that all domain controllers in the network are properly authenticated and secure. Enterprise CAs also provide additional features such as certificate revocation lists (CRLs) which can help detect any compromised certificates.

10. Don’t issue certificates with private key exportability enabled

When a certificate is issued with private key exportability enabled, it allows the user to extract the private key from the certificate and use it for malicious purposes. This could include signing code or documents that are not authorized by your organization, which can lead to serious security risks.

Therefore, it’s important to ensure that all certificates issued by Microsoft CA have private key exportability disabled. This will help protect your organization from potential security threats and maintain the integrity of your digital certificates.