Browsers are implementing a new JavaScript API for asynchronous clipboard access to integrate copy and paste into web applications. It is a replacement for the synchronous execCommand-based copy & paste. Async Clipboard requests doesn't block the page while waiting the process, it's a improvement over sync requests as well as simplifying events and aligning them with the Drag & Drop API.
Clipboardme is a pentester tool that can read and write content to the clipboard by just opening a link, using async clipboard API.
Text can be silently and automatically copied to the clipboard by calling writeText(), without requesting permission. Example:
<script>
navigator.clipboard.writeText('Malicious command to be copied');
</script>
Simple, huh? How dangerous it can be if the user is convinced to run the clipboard content? A windows reverse shell can be made if a user type the following shortcurt sequence after visiting the malicious website generated by clipboardme: windows+x, p, ctrl + v. No need to hit enter, just persuade the target to run that "shortcut" for an attacker take control of a windows system. This scenario can occur when the target is supposed to execute clipboard contents.
Text can be read (requires permission) from the clipboard by calling readText(). Example:
<script>
navigator.clipboard.readText().then(clipText => document.write(clipText));
</script>
Users routinely copy sensitive information like passwords and personal details to the clipboard, which could then be read by any page. Clipboardme tool can create a HTTPS malicious page to grab that content.
To help prevent abuse, clipboard access is only allowed when a page is the active tab and over secured domains (https). Pages in active tabs can write to the clipboard without requesting permission, but reading from the clipboard always requires permission.
Chrome 66, Opera 53, Chrome for Android, Opera for Android