Public service announcement: CAA records exist and allow you to whitelist the CAs you trust to issue certificates for your domain.<p><a href="https://letsencrypt.org/docs/caa/" rel="nofollow">https://letsencrypt.org/docs/caa/</a><p>You can use <a href="https://www.entrust.com/resources/tools/caa-lookup" rel="nofollow">https://www.entrust.com/resources/tools/caa-lookup</a> (or e.g. `dig caa paypal.com`) to see if any domain is protected.<p><a href="https://isc.sans.edu/diary/26738" rel="nofollow">https://isc.sans.edu/diary/26738</a> is a cautionary study from 2020 indicating only 3% of the Alexa top 1M had CAA records. And just now, I've seen numerous news and government sites that do not have CAA enabled... making them vulnerable to issuance bugs like this on CAs they may never have heard of, and thus making their readership/constituencies vulnerable to misinformation and fraud, especially in the context of a potential multifaceted attack against router infrastructure to perform MITM attacks at scale.<p>Of course, you'll want to make sure you don't accidentally disavow an important subdomain where an engineer used a different CA than your usual suspects. But looking at all historic issuers for your domain hierarchies on transparency logs using e.g. <a href="https://crt.sh/" rel="nofollow">https://crt.sh/</a> might be a good place to start.<p>It's also good to monitor certificate transparency logs, but then the onus is on your security team to react if an incident occurs. Proactive controls are vital as well, and IMHO CAA avoids many of the downsides of pinning.
So I guess you couldn't get certificates for any random (MX) domain, only for those where you can obtain an inbox / user account. Still really bad, especially for things like gmail.com, but also larger enterprises. Intense.
This is a ... pretty serious oversight.<p>But at least it initially appears SSL.com is taking it seriously, we'll have to see what the report says.
The whole PKI concept is dead anyway. Users have been trained to bypass certificate warnings by CA store wars between browsers and OSes, MitM corporate SSL proxies a-la ZScaler / Intune, corporate self signing CAs for intranets and whatnot, blindfolded public CAs giving certs to whatever.
And remember kids: there's hundreds of CAs, they all implement validation independently, and you just need <i>one</i> to do <i>one</i> of the three validation methods wrong to make any cert you want. And there's two dozen different attacks that work aside from bugs in validation. Cert validation is swiss cheese.<p>But there's a fix: have the registrars confirm authority to issue certs using a public key uploaded by the domain owner. The CSR contains a request signed by the same domain owner key. The CA sends the CSR to the registrar, the registrar verifies it was signed by the same key they have, then they send back a newly signed object (that the eventual-https-end-user can later confirm was signed by the registrar, so everybody knows that every step of the way was confirmed cryptographically). This ensures a single secure authorization by the actual domain owner, verified by the registrar of the domain. All you have to change is how the CA validates, and the registrar needs to handle an extra step or two. Solves 95% of the vulnerabilities.<p>....but nobody's going to do that, because the fact that Web PKI is swiss cheese hasn't threatened a big enough business yet. Once money or politics is threatened, they'll fix it.