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It looks like CAA does not prevent bad CAs at all? A rogue CA can just skip CAA altogether, no?
by riobard 7y ago
It looks like CAA does not prevent bad CAs at all? A rogue CA can just skip CAA altogether, no?
- JoachimSchipper 7y agoRogue CAs can do almost anything, but the browsers will kill any CA that is found to be (repeatedly) mis-issuing. And checking the CAA has apparently been in the CA/Browser Forum Baseline Requirements since 2017. That said, LetsEncrypt just had a nasty bug around CAA checking, and ended up not quite revoking all certificates for which insufficient checks had been executed: https://community.letsencrypt.org/t/2020-02-29-caa-rechecking-bug/114591 https://community.letsencrypt.org/t/2020-02-29-caa-recheckin....
- crote 7y agoTheoretically, a client could also query the record and check it against the certificate presented. That would basically be the same as a DANE CA constraint. I'm not aware of anyone actually doing this, though. Certificate Transparency requirements are probably enough to prevent any CA from attempting to cheat with CAA.
- tialaramex 7y agoDon't do this. CAA is not "This is the list of CAs that are trustworthy for this domain". CAA is "This is the list of CAs that can issue for this domain right at this precise moment". If you aren't a CA you should only be looking at CAA either to debug a weird problem, out of curiosity or for some research purpose. Do not use it to make security decisions if you are not a CA.