4 ms·

WoSign is one of the other CAs offering this option. It is unclear to me how TXT verification would have prevent this. The article indicates that the attackers

by pfg 11y ago

WoSign is one of the other CAs offering this option. It is unclear to me how TXT verification would have prevent this. The article indicates that the attackers created the subdomain and pointed it at a server they controlled; this means DNS was compromised and creating a TXT record wouldn't have been a problem. Domain owners which are worried about Let's Encrypt can opt to create a CAA DNS record that limits CAs allowed to issue certificates to ones they trust. CA/B BR can be found here[1]. [1]: https://cabforum.org/wp-content/uploads/Baseline_Requirements_V1_3_1.pdf https://cabforum.org/wp-content/uploads/Baseline_Requirement...

supermatt 11y ago
I simply see it as an additional (and unnecessary) attack vector. If you are unable to hijack the DNS servers or poison/spoof the cache used by the CA, then you have the luxury of a whole new (and often WAY more insecure) attack surface. Then you have a cert for that domain which can be used for other, more targeted purposes. EDIT: IGNORE BELOW, I WAS ASSUMING THAT LETS ENCRYPT LETS YOU VALIDATE SUBDOMAINS FROM THE TLD, BUT THIS DOEST SEEM TO BE THE CASE FROM THE DOCS. e.g. 1) Wifi access point uses https://login.wifiprovider.com https://login.wifiprovider.com to authenticate users. This is clamped down as tight as possible. Theres no way i'm getting in to that beastie. 2) Their brochure site located at http://www.wifiprovider.com http://www.wifiprovider.com. It was made by some ad agency and probably allows you to log in with test/test or uses some crappy custom CMS that allows SQL injections or even allows you to log in with a "wildcard" password... (this is INSANELY common). Its just a brochure site, and its not linked to the super-secure login systems in any way. 3) By breaking into this crappy brochure site, I can get a cert from a valid CA for the subdomain https://login.wifiprovider.com https://login.wifiprovider.com that allows me to sit at an access point, spoofing DNS and capturing valid login details. That doesn't seem right to me.
- pfg 11y ago
  No, with Let's Encrypt you would have to have full control over contents of login.wifiprovider.com to get a certificate for that domain. Specifically, you'd have to be able to serve a token at http://login.wifiprovider.com/.well-known/acme-challenge/random Verifying ownership of wifiprovider.com that way would not automatically allow you to get certificates for subdomains too.
  - supermatt 11y ago
    Thanks. I was assuming it would work the same as other CAs in that respect. I'm still not sure about this mechanism of verification, but good to know that my example scenario cant exist.

by pfg 11y ago

supermatt 11y ago

I simply see it as an additional (and unnecessary) attack vector. If you are unable to hijack the DNS servers or poison/spoof the cache used by the CA, then you have the luxury of a whole new (and often WAY more insecure) attack surface. Then you have a cert for that domain which can be used for other, more targeted purposes. EDIT: IGNORE BELOW, I WAS ASSUMING THAT LETS ENCRYPT LETS YOU VALIDATE SUBDOMAINS FROM THE TLD, BUT THIS DOEST SEEM TO BE THE CASE FROM THE DOCS. e.g. 1) Wifi access point uses https://login.wifiprovider.com https://login.wifiprovider.com to authenticate users. This is clamped down as tight as possible. Theres no way i'm getting in to that beastie. 2) Their brochure site located at http://www.wifiprovider.com http://www.wifiprovider.com. It was made by some ad agency and probably allows you to log in with test/test or uses some crappy custom CMS that allows SQL injections or even allows you to log in with a "wildcard" password... (this is INSANELY common). Its just a brochure site, and its not linked to the super-secure login systems in any way. 3) By breaking into this crappy brochure site, I can get a cert from a valid CA for the subdomain https://login.wifiprovider.com https://login.wifiprovider.com that allows me to sit at an access point, spoofing DNS and capturing valid login details. That doesn't seem right to me.

pfg 11y ago
No, with Let's Encrypt you would have to have full control over contents of login.wifiprovider.com to get a certificate for that domain. Specifically, you'd have to be able to serve a token at http://login.wifiprovider.com/.well-known/acme-challenge/random Verifying ownership of wifiprovider.com that way would not automatically allow you to get certificates for subdomains too.
- supermatt 11y ago
  Thanks. I was assuming it would work the same as other CAs in that respect. I'm still not sure about this mechanism of verification, but good to know that my example scenario cant exist.