I was reading this article about the fraudulent certificates from Comodo back in 2011. It talks about domain impersonation.

I understand that a fake website could be secured with the fraudulent certificates but wouldn't the domain still be a fake one and a dead giveaway? Is this kind of attack related with DNS in any way?

Also, the author says "one cert was for "global trustee" — not a domain name. That was probably a malicious CA certificate that could be used to flawlessly impersonate any domain on the Web." What the hell is a global trustee?

2 Answers 2


There are multiple ways to exploit a compromised certificate.

If you have a compromised website certificate, you need to get people onto your server when they type the address of the compromised one. This can be done:

  • By getting control of a DNS server, there you can basically change the association of a website URL to your server IP address.
  • By performing a DNS cache poisoning attack
  • By performing a Man in the Middle attack (e.g. you own a router) between your target and the website, thus redirecting him to your own server

If you have compromised a root CA certificate, you can do even better. Since you have the "master" key you can forge false certificate in the name of whoever you want. Therefore you are able to impersonate any website. This is mostly valuable to someone who can fully control a DNS server (closed internet countries for example) as they can invisibly spy onto each and any internet connections made on any website, since they can forge certificate on the fly and perform man in the middle attacks.

  • 2
    Compromised Root CAs are also useful to any MitM between the client and its Internet gateway. That's essentially how corporate SSL proxies work, though in those cases the Root CA isn't technically "compromised".
    – Iszi
    Mar 9, 2015 at 15:27
  • 5
    You're forgetting about direct MITM attacks: if I control a router in the path between you and the target system, I am free to redirect all traffic to my own system and perform a MITM that way without messing with DNS. I could use any and all compromized certs (root or otherwise) in such a case. "free wifi", anyone ?
    – Stephane
    Mar 9, 2015 at 16:13
  • 1
    Quite true @Stephane, edited accordingly.
    – M'vy
    Mar 9, 2015 at 16:15

A Certificate Signing Request (CSR) sent to a Certificate Authority (CA) contains a Public Key, so merely having a hooky TLS cert wouldn't be enough to get up to bad business: you'd also need the Secret Key used to cut the Public Key in the CSR. Finally, you'd need to hack the victim's DNS to redirect traffic. If your security is this bad, TLS certs are not your problem... Certainly possible to compromise TLS, but not easy or straightforward.

Now in the incident you reference, the Iranian hacker(s) compromised a Comodo reseller CA, transmitting their-the hackers'- own Public Key with the CSR- so they had the Secret key relating to the Public Key sent to the CA- they did not need to thieve it from their victim. So they were most of the way there, but they'd still need to hack DNS to redirect traffic to their hooky server(s). Merely having a compromised cert won't do anything until you can get traffic flowing to the host it's configured on

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