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Something that's always confused/concerned me - at least on Mac - is that when I get asked for a 2FA code logging into the icloud web UI or similar, the same co

Something that's always confused/concerned me - at least on Mac - is that when I get asked for a 2FA code logging into the icloud web UI or similar, the same computer I'm logging in from pops up a popup with the code the Apple site is requesting. Wonder if that sort of thing comes into play here - if you are trying to do something "untrusted" on a device, the trust check shouldn't rely on that same device? But then if you only had a single device you're in trouble...

nerdponx 4y ago
I imagine the problem is that, from the perspective of the web browser, the computer you happen to be using is a separate device, because it's a separate logged-in application. Seems like an obvious hole, but I don't know how you would fix that.
judge2020 4y ago
On Safari in latest macOS/iOS, it pops up an official prompt for signing into appleid.apple.com instead of having you remember and enter a code[0], so it becomes "you either need to use the local authentication factor, eg. face ID to sign in, or be in possession of an unlocked device and know the password". The real question here, IMO, is how do you prevent against this. Because to the Apple engineers in the US of A, having your phone stolen at gunpoint is almost unheard of, and getting it swiped from your hand is also barely a problem anymore since thieves in the US typically don't go through all this effort to phish the Apple ID password from you (at most they sell it to a 3p service that ships it overseas to China for teardowns and parts salvaging). 0: https://apple.stackexchange.com/q/382190 https://apple.stackexchange.com/q/382190 (note that it prompts for local user account password because the long-lived token that performs a new grant for the Safari session is stored in local Keychain; so if you have touch ID or watch unlock on your Mac, it'll use that first)
krisoft 4y ago
The web session is untrusted, and they have a trusted connection to the OS known to belong you. Don’t know how it is implemented exactly, but on the OS level they can do a lot of clever tricks. From their servers they can literally send a challenge-response protocol to the secure enclave of your computer, thus verifying that on the other end of the encrypted connection they are trully talking with a computer manufactured by them, and that computer is the one which is registered to your account. If they implement this correctly they can make an attack against this chain of trust very costly. On the other hand on the web they get a http querry with some cookie attached. Maybe. Lot harder to gain the same level of assurances there. And a simple cross site scripting attack, or a compromised browser extension can steal said cookie.
- majormajor 4y ago
  > The web session is untrusted, and they have a trusted connection to the OS known to belong you. Known to belong to me, yes. Known to be in my possession, no. You'd still need one further thing to go on as far as I can figure - I'd need the password to type into my browser first - but treating "browser session" and "machine the browser is running on" as separate levels of trust seems naive in terms of what someone who steals the machine can do.
  - deleted 4y ago
    [deleted]
  - bryan_w 4y ago
    I don't know the exact workings, but usually the authentication popup should popup with at least 1 other factor to challenge(e.g. touchid or password) if it hasn't asked recently. That way it uses 1) something you are (touchID) and something you have (Validation from a known good device) as the 2 factors.

nerdponx 4y ago

I imagine the problem is that, from the perspective of the web browser, the computer you happen to be using is a separate device, because it's a separate logged-in application. Seems like an obvious hole, but I don't know how you would fix that.

judge2020 4y ago

On Safari in latest macOS/iOS, it pops up an official prompt for signing into appleid.apple.com instead of having you remember and enter a code[0], so it becomes "you either need to use the local authentication factor, eg. face ID to sign in, or be in possession of an unlocked device and know the password". The real question here, IMO, is how do you prevent against this. Because to the Apple engineers in the US of A, having your phone stolen at gunpoint is almost unheard of, and getting it swiped from your hand is also barely a problem anymore since thieves in the US typically don't go through all this effort to phish the Apple ID password from you (at most they sell it to a 3p service that ships it overseas to China for teardowns and parts salvaging). 0: https://apple.stackexchange.com/q/382190 https://apple.stackexchange.com/q/382190 (note that it prompts for local user account password because the long-lived token that performs a new grant for the Safari session is stored in local Keychain; so if you have touch ID or watch unlock on your Mac, it'll use that first)

krisoft 4y ago

The web session is untrusted, and they have a trusted connection to the OS known to belong you. Don’t know how it is implemented exactly, but on the OS level they can do a lot of clever tricks. From their servers they can literally send a challenge-response protocol to the secure enclave of your computer, thus verifying that on the other end of the encrypted connection they are trully talking with a computer manufactured by them, and that computer is the one which is registered to your account. If they implement this correctly they can make an attack against this chain of trust very costly. On the other hand on the web they get a http querry with some cookie attached. Maybe. Lot harder to gain the same level of assurances there. And a simple cross site scripting attack, or a compromised browser extension can steal said cookie.

majormajor 4y ago
> The web session is untrusted, and they have a trusted connection to the OS known to belong you. Known to belong to me, yes. Known to be in my possession, no. You'd still need one further thing to go on as far as I can figure - I'd need the password to type into my browser first - but treating "browser session" and "machine the browser is running on" as separate levels of trust seems naive in terms of what someone who steals the machine can do.
- deleted 4y ago
  [deleted]
- bryan_w 4y ago
  I don't know the exact workings, but usually the authentication popup should popup with at least 1 other factor to challenge(e.g. touchid or password) if it hasn't asked recently. That way it uses 1) something you are (touchID) and something you have (Validation from a known good device) as the 2 factors.