It's even WORSE than I thought.

If a miscreant steals your iPhone or iPad, either unlocked or after watching you enter its passcode, they may be able to access all of your data in iCloud and in your AppleID cloud settings using a browser - even if you configured Screen Time Restrictions to limit access to critical data.

Here's how (where it reads "Touch ID" replace that with "Face ID" if your iDevice isn't equipped with a fingerprint scanner);

Assuming that you've NOT configured biometrics to unlock your iPhone or iPad (OR you've turned off 'Settings' > 'Touch ID and Passcode' > 'Password Autofill'), and:

You open, for example using Safari,
https://appleid.apple.com/sign-in
or
https://icloud.com and tap 'Sign in'
and:

You tap the (x) at the top right of the box that pops up at the bottom of the screen, and:

You tap in the field labeled "Email or phone number", and:

At the bottom of the screen, in the light gray box reading "Sign in to apple.com with your saved passkey?", you tap the blue button that reads:

Use "<your icloud.com email address>"

then the browser you're using is logged in to your AppleID account or to your iCloud account respectively.

Consequences
In your Apple ID account, you (or an attacker who does this) can see all -and edit most- of your account details. I've not tested it but they may now be able to lock *you* out of your account.

In your iCloud account they can choose 'Locate device' and disable *any other* iDevice you may have.

This is *even* true if you've configured "Screen time" restrictions in such a way [1] that a thief of your iDevice, who succeeds in unlocking it's screen (*), CANNOT view your account details ar the top of 'Settings', while it even fully hides the 'Touch ID and Passcode' submenu entry in 'Settings'.

(*) For example, after they watched you enter your passcode (see WSJ's Joanna Stern's video's that I referred to in my previous toot) - OR IF THEY SIMPLY STOLE IT FROM YOU IN AN UNLOCKED STATE!

[1] https://www.ghacks.net/2024/01/31/how-to-block-account-changes-on-iphone-using-screen-time/

Mitigations
Screen Time Restrictions [1] *does* seem to add an extra defensive layer, albeit probably insufficient.

After enabling it (note that it takes about a minute or so before all protections are actally in place, so be patient), when logged in to your Apple ID account using a browser, doing most (if not all) things labeled 'Continue on device...' do not work (no notification will be received by the iDevice). However, an attacker can probably still wreak havoc.

It's best to configure biometrics EVEN if you don't intend to use it to unlock your iDevice(s).

Note: personally I've configured only my pinky finger to unlock the screen of my iPhone SE2. One advantage is that I can unlock my iPhone in public places without (most of the times) having to enter my screen unlock passcode.

IMPORTANT: after configuring biometrics, confirm that 'Settings' > 'Touch ID and Passcode' > 'Password Autofill' is ON.

@webhat
@rmondello

@webhat : Passwordless actually exists on iPhone or iPad under realistic circumstances - that is, not taking into account unlocking the screen (using a PIN, a password or biometrics).

Consider the situation when some stranger borrows your iPhone to make a phone call, or you let your child play a game on your iPad: in such cases they may be able to log in as you onto various websites. That is, without knowing your screen unlock code (or somehow being able to simulate your biometrics).

On specific websites this even also works when using passkeys (no PIN, password or biometrics is required to use the passkey).

It obviously is a vulnerability. But after I filed a bug report in June 2023, Apple denied that it is. And they've not fixed it either.

BTW this works (on iPhone or iPad) in Safari, Firefox, Edge and Chrome (except that in Chrome, "passkey without local auth", only works if, in condition below, only iCloud Keychain is enabled and no other 'optional' password manager - such as KeePassium).

The conditions are:

The password or passkey is stored in iCloud KeyChain;

EITHER: you've NOT configured any biometrics to unlock the screen (meaning that you must use a pincode or a password to unlock the screen - a use case quite common because some people don't like to use, or don't trust, biometrics),

OR: (not common, I found it during testing) 'Settings' > 'Touch ID and Passcode': 'Password Autofill' is OFF;

In 'Settings' > 'Passwords' > 'Password Options' (all quite common):
• 'Autofill Passwords and Passkeys' is ON;
• ' iCloud Keychain' is ON;
• Optionally another password manager is enabled (in my iPhone 'KeePassium' is ON).

Passkeys only: (this is irrelevant for passwords, and applies only to iOS and iPadOS versions that support passkeys): the website you (or the borrower of your iDevice) want to sign in to (using your account) must support "WebAuthn Conditional UI" [1] AND it must specify:
    'User Verification': 'Preferred'
(the latter value, stupidly, is the WebAuthn default; the other options are 'Discouraged' and 'Required').

[1] https://github.com/w3c/webauthn/wiki/Explainer:-WebAuthn-Conditional-UI

In short, "WebAuthn Conditional UI" means that the website ALSO accepts a passkey in case you activate (tap in and see a blinking cursor) the user-ID input field (instead of tapping a button labeled e.g. "Sign in using passkey"). Doing that will invoke iCloud KeyChain and lets you select the right passkey.

Two examples (there are more) of such websites (for free testing purposes) are:
• https://passkeys-demo.appspot.com
• https://webauthn.io

AND, NOTABLY, Apple's production SSO site: https:⧸⧸idmsa.apple.com

Note that your browser is redirected to the idmsa site (in order to SSO to Apple) when you open the bugreport that I filed in June 2023:
• https://security.apple.com/signin?path=reports/OE19476493072

Here's the recipe for passwords:

Ensure that conditions , and mentioned above are met;

Open a website where you have an account with it's credentials saved in iCkoud Keychain. Invoke the log in screen and tap into the user-ID field;

Tap the proposed account name. Now iCloud Keychain autofills your user-ID and passwords into the right fields.

And the recipe for passkeys:

Ensure that conditions , , and mentioned above are met;

Open https://security.apple.com/signin?path=reports/OE19476493072

A box pops up from the bottom of the screen. Tap the X at the top-right to close it.

Tap in the input field "Email or Phone Number", then tap your iCloud ID at the bottom of your screen. Now you will be logged in to Apple without using local auth.

Note that you'll probably see a "403 access denied" error, because (although you HAVE logged in) you are not *authorized* to view te bug report.

This is passwordless 1FA because the possession of the (unlocked) device suffices.