Microsoft Disables Preview In File Explorer To Block Attacks (bleepingcomputer.com)
(Monday October 27, 2025 @12:52PM (EditorDavid)
from the explorer-horrors dept.)
Slashdot reader [1]joshuark writes:
> Microsoft says that the File Explorer (formerly Windows Explorer) now automatically blocks previews for files downloaded from the Internet to block credential theft attacks via malicious documents, [2]according to a report from BleepingComputer . This attack vector is particularly concerning because it requires no user interaction beyond selecting a file to preview and removes the need to trick a target into actually opening or executing it on their system.
>
> For most users, no action is required since the protection is enabled automatically with the October 2025 security update, and existing workflows remain unaffected unless you regularly preview downloaded files.
>
> "This change is designed to enhance security by preventing a vulnerability that could leak NTLM hashes when users preview potentially unsafe files," [3]Microsoft says in a support document published Wednesday .
>
> It is important to note that this may not take effect immediately and could require signing out and signing back in.
[1] https://slashdot.org/~joshuark
[2] https://www.bleepingcomputer.com/news/microsoft/microsoft-disables-preview-pane-for-downloads-to-block-ntlm-theft-attacks/
[3] https://support.microsoft.com/en-us/topic/file-explorer-automatically-disables-the-preview-feature-for-files-downloaded-from-the-internet-56d55920-6187-4aae-a4f6-102454ef61fb
> Microsoft says that the File Explorer (formerly Windows Explorer) now automatically blocks previews for files downloaded from the Internet to block credential theft attacks via malicious documents, [2]according to a report from BleepingComputer . This attack vector is particularly concerning because it requires no user interaction beyond selecting a file to preview and removes the need to trick a target into actually opening or executing it on their system.
>
> For most users, no action is required since the protection is enabled automatically with the October 2025 security update, and existing workflows remain unaffected unless you regularly preview downloaded files.
>
> "This change is designed to enhance security by preventing a vulnerability that could leak NTLM hashes when users preview potentially unsafe files," [3]Microsoft says in a support document published Wednesday .
>
> It is important to note that this may not take effect immediately and could require signing out and signing back in.
[1] https://slashdot.org/~joshuark
[2] https://www.bleepingcomputer.com/news/microsoft/microsoft-disables-preview-pane-for-downloads-to-block-ntlm-theft-attacks/
[3] https://support.microsoft.com/en-us/topic/file-explorer-automatically-disables-the-preview-feature-for-files-downloaded-from-the-internet-56d55920-6187-4aae-a4f6-102454ef61fb