Would be so convenient to have an intermediate CA cert constrained to *.my-name.com to avoid situations like this. Being forced to either use a private PKI infrastructure or using wildcards to not leak host names is so annoying.
Because the most popular browsers (at least Chrome and Safari) generally require CT logged certificates, if you want to successfully perform a MitM attack against any user, even just some individual user, even controlling a CA, you still can't do so without publishing your fraudulent certificate to a CT log.
This is the important function of the CT log. It is an effective balance against compromised CAs and governments that might abuse CAs, because it causes such attacks to become quickly tamper-evident.
I don't think it would be possible for a system like this to be effective without publishing the actual certificate to the log.
Let's say that browser is fine with CT if either leaf or intermediate certificate is logged.
If you need to issue fake certificate, you need to either log it, or you need to issue fake intermediate certificate and log it.
Either way it's visible to website owner (and other people likely won't care anyway).
Public CT logs mean that the property of transparent certificate issuance extends to the entire Internet, which is good. If you want private certs, you can use a private CA and deploy it to the machines in your domain. Totally reasonable alternative in my opinion.
If your organisation is competent enough to handle an intermediate CA certificate safely, you're certainly competent to handle a wildcard cert safely which is a much easier task.
Sadly it's unlikely you'll ever see the Name Constraints extension adopted. All it takes is one model of 15 year old smart TV failing to respect it, and the CA/Browser Forum will consider it too dangerous to allow.
In my current org we have hundreds of TLS termination "configuration points" (cdn's & cloud loadbalancers / networking appliances / k8s ingress controllers / raw VM's). We have standardised on ACME issued certs for almost everything. Using a wildcard certificate would force us back to manual cert updating procedures, or finicky scripts. Undoubtedly causing issues when certs become expired.
(Not to mention the trust boundaries. An org can be competent enough to handle an in-house CA securely, and simultaneously have a bunch of quasi-sloppy vendors for stuff like the visitor badge kiosk.)
But I sadly agree that it will probably never happen…
Just because I trust a server to hold the cert for preview.example.com doesn’t mean I’d want it to be able to pose as prod.example.com, for example.
Having domain-constrained sub-CA certificates granted by the exact same mechanism we use for wildcard certs today would combine the advantages of both.
There are certainly other strategies and best practices that can mitigate the risk in this scenario, but not using wildcards is a good one to include.
That's not every organization.
I maintain many groups of /related/ servers (including dynamic ones which appear and disappear at whim). There, a wildcard makes a lot of sense. If I have https://[username].[domain]/, https://[git project].[domain]/, https://[client].[domain]/ or similar, that integrates nicely with a lot of security infrastructure in ways which http://[domain]/client/ don't.
E.g. A network can filter https based on domains, but can't look inside the envelope. A browser will highlight domains to users who want to know where they are. Etc.
There are also many good reasons why managing one credential per server (which can map to many domains) is better practice than managing a dizzying array of credentials.
So I agree about the general best practice, but there are exceptions. Mandating (as opposed to recommending / encouraging) non-universal best practices is usually bad practice.
Recommending encouraging non-wildcard certs is the optimal strategy. Only thing I would add, is recommending default to non-wildcard and evaluate deviations case by case.
Yours is not an argument against wildcard certificates! Yes, like, everything else ever, wildcard certificates can be misused.
They were proposed here as an alternative to domain-restricted sub-CAs, but GP and me have given counterexamples as to why they're not (or at least not without downsides).
> No one is saying wildcard certificates should be mandatory.
Nor am I saying they shouldn't ever be used.
You may interpret it differently, but to me:
> Why? As I understand it, the domain owner can assign the name you “trust” to any server already. Might as well trust all names by that domain owner.
Essentially means "default to a wildcard." My example is absolutely a good reason why you should not default to a wildcard. There are situations where they make good sense. I use them myself. It's a terrible idea to use them everywhere and always, which is usually what ends up happening when wildcard certs are the default approach.
Dave can test his stuff on a newly bought domain for testing or the internal domains.
But yeah generally speaking, it's best to avoid wildcards unless there's an actual benefit to using them, even when it's not a prod domain.
every branch
* several test data sets
* several feature flag / configuration sets
* ...