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Comment by eeZah7Ux | Hacker News Reader

> It protects against phishing

Not so much. U2F proves only that the user tapped the device when asked to do so.

You still have to trust your browser and your entire desktop that the tap will be used to log in to the service you are browsing instead of e.g. quietly logging to your home banking.

To prevent "tap hijacking" we need a display on the U2F key to show the URL/service you are really authenticating to.

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What you're describing is a different attack vector than phishing. I would describe it as malware. The classic phishing attack is to convince a target to visit a web page with a subtly different URL than the real thing, where they enter their credentials, which could include most second factors (OTP codes or push notifications). With U2F however, the browser will pass the URL of the requesting site to the U2F token, and that will be signed by the U2F token. The resulting signature cannot be used to login to the real service. You have to own the user's device or browser in order to do a phishing attack with U2F. And if you own the device or browser, it's probably easier to steal the short lived session auth credentials than it is to man in the middle U2F. You are correct, however, that U2F is not resistant to malware. Unfortunately, nothing really is, and it's not an easy problem to solve.

No: the phishing attack leads the browser to parse and run malicious javascript and HTML.

If the phishing page is then able to compromise the browser the security is breached.

For example it could trick the browser into presenting the legitimate URL to the U2F token, or wait for the user to log on the home banking site for real and then perform transaction, or many other attacks.

Assuming valid FIDO2/U2F implementation and same origin policy, this shouldn't be an issue. A browser will enforce that the APP-ID/domain name submitted to the token is the same as the origin requesting it. So in order to be tricked into signing into your bank, it would actually have to be your bank requesting the authentication. HTTPS is also a requirement.

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