Microsoft has disabled one of the most convenient features of File Explorer in Windows 11: previewing certain files downloaded from the Internet.
The change came with the October security update, and according to the company, it responds to security reasons after a serious vulnerability was detected.
Microsoft explains that the preview of downloaded files was disabled to fix a bug that could leak NTLM hashesa type of sensitive information that could expose the user’s credentials.
The problem was triggered when the system tried to preview files that contained HTML tags with references to external paths, allowing attackers to capture private data over unsecured connections.
To avoid this risk, Windows by default blocks the preview of files with the “Mark of the Web” label, a mark that the system automatically adds to all files downloaded from the Internet.
Thus, when the user tries to open the preview of one of these files, the system will display a warning: «The file you are trying to preview could damage your computer. If you trust the file and the source from which it comes, open it to see its contents.»
Microsoft clarifies that this measure it does not prevent files from being opened or affect other system functions. If you trust the origin of the file, the user can manually remove the mark by right-clicking on the file, entering Properties and checking the “Unlock” option.
This restriction affects Windows 11 and several versions of Windows Server, although it does not apply to Windows 10. In the latter, only computers enrolled in the extended update program will continue to receive security updates for another year.
With this decision, Microsoft reinforces protection measures against one of the most common attack vectors, which are files downloaded from the Internet.
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Tags: Windows 11