Bulletproof TLS Newsletter #32
CAA is now mandatory
28 September 2017
Author: Hanno Böck

This issue was distributed to 40,154 email subscribers.

Bulletproof TLS Newsletter is a free periodic newsletter bringing you commentary and news surrounding SSL/TLS and Internet PKI, designed to keep you informed about the latest developments in this space.

In this issue:

  1. CAA is now mandatory
  2. Short news

CAA is now mandatory

A new DNS record type should improve the security of certificate issuance. Certificate Authority Authorization (CAA) was specified in RFC 6844 in 2013, but until recently implementing it wasn’t required. That has now changed. The CA/Browser Forum has decided that starting September 8, all certificate authorities must check CAA. CAA allows domain owners to define in a DNS record which certificate authorities are allowed to issue certificates for them.

Shortly after the deadline, various people tried to verify whether certificate authorities properly check CAA. It was revealed that Comodo—the company that invented CAA—failed to check CAA records, and this was independently verified by various people. In an incident report, Comodo confirmed the issue and explained that it was due to an error in the interaction with the dig command.

Various other CAs failed to properly handle corner cases with CAA, particularly in combination with DNSSEC.

Andrew Ayer has created a CAA test suite. He also operates a CAA record generator for the company SSLMate.

Short news