Security Experts:

Chrome Bug Allows Webpages to Replace Clipboard Contents

A vulnerability in Google Chrome – and in all Chromium-based browsers – allows webpages to replace the contents of the system clipboard without the user’s consent or interaction.

The issue exists because the browser does not have the necessary safeguards to prevent sites from writing to the clipboard.

According to developer Jeff Johnson, the bug was introduced in Chrome 104, when a requirement for a user gesture to copy content to the clipboard was broken.

Because of that, when a user visits a specially crafted webpage, the content of the system clipboard may be replaced with content defined on that page.

The same issue is present in Firefox and Safari as well, the developer says. However, while the bug can be triggered in Chrome without user interaction, some form of gesture is required to exploit it in Firefox and Safari.

According to Johnson, when on the crafted page, if the user triggers a ‘copy’ or ‘cut’ command, clicks on a link, or simply scrolls down or up (using either the mouse or the keyboard), the page is granted the permission to overwrite the system clipboard.

The developer has created a demo webpage to showcase the vulnerability. SecurityWeek was able to verify the issue on the most recent Chrome release (version 105), but could not reproduce it in Firefox.

“The potential for maliciousness should be obvious. While you're navigating a web page, the page can without your knowledge erase the current contents of your system clipboard, which may have been valuable to you, and replace them with anything the page wants, which could be dangerous to you the next time you paste,” the developer notes.

Cybercriminals have been observed targeting the clipboard content in attacks meant to hijack a victim’s cryptocurrency transactions. As part of such attacks, malware is typically used to replace in the clipboard a crypto wallet address with that of a wallet controlled by the attackers.

Johnson says he has also checked whether a webpage may be able to read the content of the clipboard with arbitrary gestures, but that the results of his tests were negative. A ‘clipboard-read’ permission needs to be granted before that.

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