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It seemed odd to me that a Web site could write to or read from the clipboard without the user approving it. That would be a pretty obvious security and privacy issue. From what I gather, on Chrome sites can write to the clipboard without approval, but they need approval to read.
On Firefox and others any access requires permission. Thus this exploit seems limited to Chrome users.@SkaveRat pointed out that it doesn't require permission, only interaction. So likely there's a button that's clicked that writes to the clipboard, and most browsers are susceptible to this.
not when there was a user intent like clicking a button.
For example in this screenshot, it's likely that there's only the "verify I'm human" button first, you click it, the steps pop up, and at the same time the command ist copied into your clipboard
Exactly, copy requires a click but there's no rule that the copy button has to look like anything particular
It doesn't necessarily need a click - it can be triggered by a keypress too (eg at my workplace we have a few internal pages where you can press a keyboard shortcut to copy a shortened URL for the current page).
It has to be something the browser considers a user interaction, meaning the user has expressed an intent to perform the action. That's usually a button press or keypress.
Why isn't the default behavior for browsers to not allow access to the clipboard? Similar to how it prompts you for access to camera/microphone
Edit: On a per-site basis, like if you use the Zoom website it asks you for access to the webcam, would something like this work for clipboard as well or would it break stuff?
There is no inherent security problem with changing the content of the clipboard. That doesn't do anything until the user pastes it somewhere; of course if that "somewhere" is a command prompt, then that is a security problem, but users really ought to check what they're pasting there before they execute it (yeah, I know, "ought to").
It would be possible to do it the way you say, but that would mean that the user would need to allow that for many websites; I don't think copying from apps like Google Docs would work anymore, and "here's your access token, click here to copy it to the clipboard" features certainly wouldn't.
The screenshot in the OP would then probably be changed to include a step "click: allow clipboard access"; I think most people who fall for the screenshot in the OP would also fall for that.
Exactly. Furthermore they'd probably just include it in those instructions "Step 1: when the box pops up with clipboard press allow"
The browser can't access your clipboard contents without permission, but it can place text into the clipboard.
The problem is people the talking the copied text and pasting it into the command prompt.
Yeah that's what I'm curious about; I'm used to copying code snippets or codes from websites by clicking a button (presumably through some browser API?), but am just now realizing that this in itself has security implications.
Using noscript or some such JS blocker would prevent this but break a lot of other things in the process. That's why I'm wondering why the API isn't locked down via some user prompt.
In Firefox, you can disable the clipboard events. I've done this for the rare case of me copy+pasting a password and forgetting to clear the clipboard after.
On Android, I've noticed that it's possible for apps to read from the clipboard, to read OTP tokens for example. Since I noticed that a while back, I've always been wary of the clipboard on any device I've used.
but it can place text into the clipboard.
Only as the result of a user interaction, for example by pressing a button.
From the Browser's viewpoint, would there be any difference if the webpage has a JS button to put something in the clipboard, or it having code running in the background that puts things into the clipboard at page load?
It's not like there's that much of a difference, as far as the Browser is concerned.
would there be any difference if the webpage has a JS button to put something in the clipboard, or it having code running in the background that puts things into the clipboard at page load?
Clicking a button shows user intent, whereas a page load doesn't. No user expects loading a page to overwrite their clipboard, but every user that clicks a "Copy to Clipboard" button does expect it.
It seemed odd to me that a Web site could write to or read from the clipboard without the user approving it
Yeah, that's a security hole that I hadn't been aware of.