Day: February 23, 2015

CVF: SPF as a Certificate Validator for SSL

In light of recent widespread MiTM goings on with Superfish and Lenovo products, I dusted off an old technique introduced in the anti-spam communities several years ago that would have prevented this, and could more importantly put a giant dent in the capabilities of government sponsored SSL MiTM.

The Core Problem

The core of the problem with SSL is twofold; after all these years, thousands of Snowden documents, and more reason to distrust governments and be paranoid about hackers more than ever, we’re still putting an enormous amount of trust into certificate authorities to:

  1. Play by the rules according to their own verification policies and never be socially engineered
  2. Never honor any secret FISA court order to issue a certificate for a targeted organization
  3. Be secure enough to never be compromised, or to always know when they’ve been compromised
  4. Never hire any rogue employees who would issue false certificates

Not only are we putting an immense trust in our CAs, but we’re also putting even more trust into our own computers, and that the root certificates loaded into our trust store are actually trustworthy. Superfish proved that to not be the case, however Superfish has only done what we’ve been doing in the security community for years to conduct pen-tests: insert a rogue certificate into the trust store of a device. We’ve done this with iOS, OSX, Windows PCs, and virtually every other operating system as well in conducting pen-tests and security audits.

Sure, there is cert pinning, you say… however in most cases, when it comes to web browsers at least, cert pinning only pins your certificate to a trusted certificate authority. In the case of Superfish’s malware, cert pinning doesn’t appear to have prevented the interception of SSL traffic whatsoever. In fact, Superfish broke the root store so badly, that in some cases, self-signed certificates could even validate! In the case of CAs that have been compromised (either by an adversary, or via secret court orders), cert pinning can also be rendered ineffective, because it still primarily depends on trusting the CA and the root store.

We have existing solid means of validating the chain of trust, but SSL is still missing one core component, and that’s a means of validating with the (now trusted) host itself, to ensure that it thinks there’s nothing fishy about your connection. Relying on the trust store alone is why, after potentially tens of thousands of website visits, none of the web browsers thought to ask, “hey why am I seeing the same cert on every website I visit?”

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