Navigating CAA DNS Records with AWS: A Deep Dive

Security and trust are at the heart of the digital landscape. In the realm of web security, SSL/TLS certificates, a staple for HTTPS, play a crucial role. As we seek continuous improvement in the certificate issuance process, AWS users can benefit from understanding the role of the CAA (Certificate Authority Authorization) DNS record.
What is a CAA DNS Record in the AWS Context?

CAA, short for Certificate Authority Authorization, is a type of DNS record that lets domain proprietors dictate which Certificate Authorities (CAs) can issue certificates for their domain. This is particularly pertinent for AWS users leveraging AWS Certificate Manager (ACM) to manage their SSL/TLS certificates.

For example, a CAA record might appear as:

ercanermis.com. CAA 0 issue "amazon.com"

This implies that only AWS ACM (represented by “amazon.com”) is permitted to issue certificates for ercanermis.com.

The CAA dig result may contain more than one record like below and it’s normal.

dig CAA ercanermis.com +short
0 issue "amazon.com"
0 issue "comodo.com"
0 issue "comodoca.com"
0 issue "letsencrypt.org"
0 issuewild "amazon.com"
0 issuewild "comodo.com"
0 issuewild "comodoca.com"
0 issuewild "letsencrypt.org"

Why AWS Users Need to Understand CAA DNS Records:

Enhanced Security on AWS: CAA records act as a barrier, preventing the accidental issuance of unauthorized certificates on your domain. This is essential for AWS users seeking to bolster their domain security in the AWS ecosystem.

Granular Control with ACM: With CAA records, AWS users get pinpoint control over their SSL/TLS certificates on ACM. This ensures that only trusted CAs, like ACM, are issuing certificates for their domain.

ACM’s Audit Mechanism: If ACM, or any CA, receives a certificate request for a domain with a CAA record that doesn’t list them, the CA will log the request and notify the domain owner. This provides AWS users with a transparent view of any unauthorized certificate requests.

Advantages for AWS Users:

• Prevention of Unauthorized Certificates: By explicitly declaring ACM as the designated CA, AWS users can ward off unauthorized entities from obtaining valid certificates for their domain within the AWS framework.
• Seamless Integration with AWS Services: Using CAA records in conjunction with ACM offers smooth integration with other AWS services, ensuring a streamlined workflow.
• Unwavering Compliance: All CAs, including ACM, are mandated to check CAA records before certificate issuance, ensuring consistent security standards across the board.

Considerations:

• ACM Maintenance: If AWS users decide to integrate or switch to another CA alongside ACM, they must remember to adjust their CAA records.
• Propagation Delays: AWS users should be aware that DNS updates, including CAA records, might have propagation delays, potentially affecting the timeline for new certificate issuance within ACM.
• Configuration Nuances: Incorrect CAA records could inadvertently block ACM from issuing legitimate certificates.

Transitioning to AWS ACM:

Before CAA records became standard, there was no uniform method allowing domain owners to express CA preferences. This meant any CA could issue a certificate for any domain, given they could validate ownership. AWS users now have a more secure, streamlined method with ACM and CAA records.
A Practical Example with AWS ACM and CloudFlare:

Imagine attempting to secure an SSL certificate via AWS ACM for ercanermis.com and *.ercanermis.com using email validation. If ercanermis.com has an existing CAA record (perhaps for another CA) and lacks a wildcard setup on CloudFlare, challenges might arise.

To navigate this:

1. Ensure you add a CAA record for AWS ACM (amazon.com) for your domain on CloudFlare.

2. For wildcard subdomains, ensure they are covered in the CAA record.

Remember, if you possess existing CAA records, introducing a new one doesn’t negate the old ones unless explicitly modified.