5 ms·

Glad to see this getting attention. Flexible SSL is an awful option that has no place in the modern encrypted web. Out of the four SSL options Cloudflare gives

by r1ch 5y ago

Glad to see this getting attention. Flexible SSL is an awful option that has no place in the modern encrypted web. Out of the four SSL options Cloudflare gives users, only one is actually secure. It's a huge foot-gun.

jrochkind1 5y ago
I assume you mean only ` Full (strict)` is secure, and not even `Full`? I happened to be recently looking at putting cloudflare in front of an S3 bucket, and it looked maybe easier/more feasible to do with `Full` instead of `Full (Strict)` -- because you can skip configuring the S3 bucket have an SSL cert for your actual front-facing domain (which can be cumbersome and/or more expensive to set up) and just let CloudFlare connect to it as `*.s3.aws.com` or whatever. As long as CloudFlare is actually requiring a trusted cert for *.s3.aws.com, are there security implications I'm missing for why this is a bad idea? (I guess AWS or someone with the keys to AWS certs could be spoofing you? Anything else?) Or in general even without reference to this use case, explain vulnerability examples/threat models for `Full` without `Strict`?
- r1ch 5y ago
  Full does not check certificates, so a MITM can supply any untrusted certificate and intercept your traffic. Only Full (Strict) does trusted cert checking.
  - ewuhic 5y ago
    "Can" theoretically, or there's a valid attack vector which one may pull off immediately in the wild?
    - captn3m0 5y ago
      The current Airtel scenario is a good demonstration I’d say.
    - r1ch 5y ago
      Cloudflare terminates SSL at the point closest to the user, so any of the ISPs between Cloudflare's POP and the origin could MITM the traffic. Normally an untrusted MITM cert would throw up a TLS error, but since the Cloudflare <-> End User part is trusted, a MITM attack with anything but Full (Strict) is undetectable to an end user. There's plenty of examples of ISPs trying this in the wild: https://www.zdnet.com/article/kazakhstan-government-is-now-intercepting-all-https-traffic/ https://www.zdnet.com/article/kazakhstan-government-is-now-i... https://www.reddit.com/r/sysadmin/comments/4vy3op/my_isp_is_trying_to_intercept_some_of_my_https/ https://www.reddit.com/r/sysadmin/comments/4vy3op/my_isp_is_... https://superuser.com/questions/176651/isp-replaces-ssl-certificates-any-solution https://superuser.com/questions/176651/isp-replaces-ssl-cert...
  - jrochkind1 5y ago
    Huh, I didn't realize Full didn't check certs at all. Why don't they have a mode that checks that the cert is valid for hostname that you have configured cloudflare to access (which *.s3.amazonaws.com already has), rather than for the end-point that the destination isn't actually answering on directly itself? Or maybe I'm misunderstanding what was up, have to mess with it more.
- sirshmooey 5y ago
  Just use a free Cloudflare Origin CA certificate and set to strict. Encryption for the whole round trip unless someone accesses origin server directly. https://developers.cloudflare.com/ssl/origin-configuration/origin-ca https://developers.cloudflare.com/ssl/origin-configuration/o...
  - jrochkind1 5y ago
    But now do I have no way to access the S3 bucket not through cloudflare?
    - tialaramex 5y ago
      You know it's supposed to have a certificate from Cloudflare, so, you can choose to trust that certificate (knowing it is correct for this purpose) or you can use tooling that doesn't care. If you mean can you present it for general access by people on the Internet, no, not really, because the certificate aren't trusted, you would need a proxy layer.
btown 5y ago
On the contrary, the idea that a mom-and-pop shop running an HTTP website on some ancient shared hosting can easily just drop in Cloudflare is a Good Thing. Sure, you're not removing the attack surface, a state actor could intercept the server-to-server connections... but at least the hacked router in your customers' coffee shop is removed from the threat model. You make it any tougher, and that HTTP website is just going to stay HTTP forever.
- captn3m0 5y ago
  Hence, my recommendation of a "Big Red Warning" on picking anything lower than Strict SSL. A user must knowingly choose this option, and many websites which picked Flexible SSL could easily be upgraded to Strict SSL today. CloudFlare must work towards upgrading these users, especially where it can easily identify that SSL is supported at the origin server (such as Shopify, GitHub etc).
- r1ch 5y ago
  The downside of such a setup is that as a user, I now have no idea if the site is actually secure. If the mom-and-pop shop is taking credit card orders and has a secure Cloudflare cert, how do I know they aren't then transmitting my credit card number and other personal data unencrypted the rest of the way? If the website was HTTP I would know as a user not to enter sensitive info. This is why I think flexible SSL is worse than no SSL. Cloudflare's own docs used to say Flexible SSL "should only be used as a last resort if you are not able to setup SSL on your own web server, but it is less secure than any other option (even “Off”)" (this has since been removed).
  - marginalia_nu 5y ago
    > The downside of such a setup is that as a user, I now have no idea if the site is actually secure. You never do. SSL is not sufficient for security. It protects against a single attack vector, that's if it's set up correctly. For all you know, the set up of the server your visiting might have be old enough to have a driver's license, with public SSH and the root password "12345".

by r1ch 5y ago

jrochkind1 5y ago

I assume you mean only ` Full (strict)` is secure, and not even `Full`? I happened to be recently looking at putting cloudflare in front of an S3 bucket, and it looked maybe easier/more feasible to do with `Full` instead of `Full (Strict)` -- because you can skip configuring the S3 bucket have an SSL cert for your actual front-facing domain (which can be cumbersome and/or more expensive to set up) and just let CloudFlare connect to it as `*.s3.aws.com` or whatever. As long as CloudFlare is actually requiring a trusted cert for *.s3.aws.com, are there security implications I'm missing for why this is a bad idea? (I guess AWS or someone with the keys to AWS certs could be spoofing you? Anything else?) Or in general even without reference to this use case, explain vulnerability examples/threat models for `Full` without `Strict`?

r1ch 5y ago
Full does not check certificates, so a MITM can supply any untrusted certificate and intercept your traffic. Only Full (Strict) does trusted cert checking.
- ewuhic 5y ago
  "Can" theoretically, or there's a valid attack vector which one may pull off immediately in the wild?
  - captn3m0 5y ago
    The current Airtel scenario is a good demonstration I’d say.
  - r1ch 5y ago
    Cloudflare terminates SSL at the point closest to the user, so any of the ISPs between Cloudflare's POP and the origin could MITM the traffic. Normally an untrusted MITM cert would throw up a TLS error, but since the Cloudflare <-> End User part is trusted, a MITM attack with anything but Full (Strict) is undetectable to an end user. There's plenty of examples of ISPs trying this in the wild: https://www.zdnet.com/article/kazakhstan-government-is-now-intercepting-all-https-traffic/ https://www.zdnet.com/article/kazakhstan-government-is-now-i... https://www.reddit.com/r/sysadmin/comments/4vy3op/my_isp_is_trying_to_intercept_some_of_my_https/ https://www.reddit.com/r/sysadmin/comments/4vy3op/my_isp_is_... https://superuser.com/questions/176651/isp-replaces-ssl-certificates-any-solution https://superuser.com/questions/176651/isp-replaces-ssl-cert...
- jrochkind1 5y ago
  Huh, I didn't realize Full didn't check certs at all. Why don't they have a mode that checks that the cert is valid for hostname that you have configured cloudflare to access (which *.s3.amazonaws.com already has), rather than for the end-point that the destination isn't actually answering on directly itself? Or maybe I'm misunderstanding what was up, have to mess with it more.
sirshmooey 5y ago
Just use a free Cloudflare Origin CA certificate and set to strict. Encryption for the whole round trip unless someone accesses origin server directly. https://developers.cloudflare.com/ssl/origin-configuration/origin-ca https://developers.cloudflare.com/ssl/origin-configuration/o...
- jrochkind1 5y ago
  But now do I have no way to access the S3 bucket not through cloudflare?
  - tialaramex 5y ago
    You know it's supposed to have a certificate from Cloudflare, so, you can choose to trust that certificate (knowing it is correct for this purpose) or you can use tooling that doesn't care. If you mean can you present it for general access by people on the Internet, no, not really, because the certificate aren't trusted, you would need a proxy layer.

btown 5y ago

On the contrary, the idea that a mom-and-pop shop running an HTTP website on some ancient shared hosting can easily just drop in Cloudflare is a Good Thing. Sure, you're not removing the attack surface, a state actor could intercept the server-to-server connections... but at least the hacked router in your customers' coffee shop is removed from the threat model. You make it any tougher, and that HTTP website is just going to stay HTTP forever.

captn3m0 5y ago
Hence, my recommendation of a "Big Red Warning" on picking anything lower than Strict SSL. A user must knowingly choose this option, and many websites which picked Flexible SSL could easily be upgraded to Strict SSL today. CloudFlare must work towards upgrading these users, especially where it can easily identify that SSL is supported at the origin server (such as Shopify, GitHub etc).
r1ch 5y ago
The downside of such a setup is that as a user, I now have no idea if the site is actually secure. If the mom-and-pop shop is taking credit card orders and has a secure Cloudflare cert, how do I know they aren't then transmitting my credit card number and other personal data unencrypted the rest of the way? If the website was HTTP I would know as a user not to enter sensitive info. This is why I think flexible SSL is worse than no SSL. Cloudflare's own docs used to say Flexible SSL "should only be used as a last resort if you are not able to setup SSL on your own web server, but it is less secure than any other option (even “Off”)" (this has since been removed).
- marginalia_nu 5y ago
  > The downside of such a setup is that as a user, I now have no idea if the site is actually secure. You never do. SSL is not sufficient for security. It protects against a single attack vector, that's if it's set up correctly. For all you know, the set up of the server your visiting might have be old enough to have a driver's license, with public SSH and the root password "12345".