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As if you needed another reason not to ever use SSO to your Google account for anything (mbin.grits.dev)

submitted 2 years ago by mozz@mbin.grits.dev to c/netsec@lemmy.world

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For some reason this only just now occurred to me: What's to stop some web site from carefully crafting an imitation of the Google "you need to sign in again" UI, storing your Google password, and storing from the other side the auth cookie from Google, so that it can then poke around through 100% of your Google content including any other site you've signed into with the same SSO login?

This is such a fundamental flaw in the whole concept that it's obviously occurred to people and they've had time to come up with something to prevent it, but I can't see how you could prevent it. Have I missed something? You might have a non-Google URL in the address bar during the faked sign-in, or you could use varying degrees of deception to attempt to make the address bar look legit, but I'd honestly be surprised if more than 20% of people even check the address bar every time they sign in to SSO. I don't.

So what's to make this not work?

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[–] slazer2au@lemmy.world 3 points 2 years ago (1 children)

That's not how it works.

When you use SSO to auth the website never sees your account credentials.

The site: Google, here are my SAML codes can you auth this person. Google: cool those SAML codes are correct, hey user what are your Google auth details?
User: here you go Google.
Google: sweet, those are valid. hey site here is a token specifically for you for this user.
Site: welcome user.

At no point does your Google password hit the site and the tokens for other services will not work with a random webapp.

[–] mozz@mbin.grits.dev 5 points 2 years ago

That's not how it works if the website serves you the genuine Oauth code.

If the website serves you a malicious imitation of the genuine Oauth code, which is crafted to make that exactly how it works, then that is in fact exactly how it works.