When will Microsoft release a fix for the security changes implemented in update KB5066835

Question

When will Microsoft release a fix for the security changes implemented in update KB5066835

Graham Cooper 0

When will Microsoft release a fix for the security changes implemented in update KB5066835?

The changes implemented in relation to previewing files is literally adding hours to my work week, forcing me to open almost every file i access on a daily basis.

I work in construction and can download hundreds of plans each day, to then have to open every one to see if I need the information it contains is frustrating and onerous.

This security update must be one of the dumbest ever implemented by Microsoft, and thats a big call after previously working in IT.

Can Microsoft please rectify this, or alternatively provide me with a purchase order so I can invoice them for the additional hours rather than my clients. Try explaining to clients the work takes loinger because of technology.
Moderator note: moved from Windows for business | Windows Client for IT Pros | Devices and deployment | Install Windows updates, features, or roles

4 answers

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Answer 1

Hi,

Just a quick follow-up to my previous reply. I also wanted to turn this off, so I’d like to share other good options I found to help restore the preview pane.

Disclaimer: These are non-Microsoft sites. The content appears reliable, but stay cautious of ads. Always research products before downloading.

Just keep in mind that doing this increases the risk of NTLM hash leaks, so please be aware of the potential security impact.

Answer 2

Hi,

Sorry to hear about your bad experience with this update. In addition to what Emma mentioned, the update is designed to address a vulnerability where attackers could trick users into downloading files that appear safe but are actually intended to steal credentials. In certain scenarios, even previewing such files could lead to the exposure of sensitive information. To reduce this risk, Microsoft has implemented a change that blocks previews of downloaded files that may contain these types of malicious exploits. For more details about this update and how you can unblock individual files, you can check this article.

If you're sure that the files are safe, you can actually use this PowerShell command to let you unblock all document files in a specific path and allows you to preview them again.

Click taskbar search, type Windows PowerShell
Right-click on it then Run as administrator
Enter this command: Unblock-File -Path "C:\Users\admin\downloads\*.pdf"
Replace the path C:\Users\admin\Downloads with the location where your files are stored. You may do this per folder.
Restart the computer and see if it works.

You may also check other commands from this article:

How to unblock previews in File Explorer

Disclaimer: This is a non-Microsoft site. The information seems reliable, but be careful with ads. Research any product before downloading.

Paulo GM 60,205 Reputation points Independent Advisor

2026-01-22T12:44:08.4466667+00:00

I would like to check whether you had the opportunity to try the suggestions I provided. Please let me know if you have any further question regarding this. :)

Answer 3

Emma1-N 3,230 Microsoft External Staff Moderator

Welcome Graham Cooper,

Thank you for reaching out to Microsoft Q&A forum. I’m sorry to hear that you’re experiencing difficulties after installing security update KB5066835.

You can try the workaround step below to troubleshoot the issue:

Uninstall KB5066835 temporarily

Settings > Windows Update > Update history (not recommended long-term due to security risks)

You can review some steps in this link - How to uninstall a Windows Update - Microsoft Support

If you’re experiencing ongoing issues caused by update KB5066835, you can send your concern via a Feedback Hub. This tool sends your report straight to the Windows engineering teams, where it becomes part of their internal prioritization process for future improvements and fixes.

I really hope that the information I gave above was helpful to you. Please feel free to reply below and let me know if you have further concern on this matter.

P.S: If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Emma1-N 3,230 Reputation points Microsoft External Staff Moderator

2026-01-22T06:27:56.95+00:00

Hi Graham Cooper,

Could you please let me know if your issue has been resolved or if you are still experiencing the difficulties?
Graham Cooper 0 Reputation points

2026-01-22T06:37:48.07+00:00

Hi Emma,

I am unable to uninstall the update. The OS was installed post this update following a HD failure and it must be incorporated in the install package used.

I am aware that you can use powershell, but I have files in too many locations to run for every folder.

It is just really frustrating that simple things are now hard.

Microsofts reasoning doesnt hold up as the preview function still works in outlook, so opening an infected file could still result in infection.

People just need to use decent anti-virus and Malware software.
Emma1-N 3,230 Reputation points Microsoft External Staff Moderator

2026-01-23T08:12:10.5133333+00:00
Hi Graham Cooper,

Thanks for taking the time to share the impact this has had on your workflow.

This behavior is by design after KB5066835 as part of a security hardening update. File Explorer will block Preview pane rendering for internet-marked files (those carrying Mark of the Web / Internet Zone).

You can find the information in these references

File Explorer automatically disables the preview feature for files downloaded from the internet - M…

October 14, 2025—KB5066835 (OS Builds 26200.6899 and 26100.6899) - Microsoft Support

Workarounds:

If you trust the file, Unblock it: right‑click > Properties > Unblock > OK

For many files, you can bulk-unblock using PowerShell

For trusted internal shares, add the share to Local intranet / Trusted sites to avoid the “Internet Zone” classification
Graham Cooper 0 Reputation points

2026-01-23T23:41:11.6333333+00:00

This should be a security option that users can opt out of. This protects those people who are less tech savvy, while allowing people who know about internet security and avoiding threats to continue working without this frustrating feature.

Yes I can use powershell, but that only acts on the files in the folder at that point in time. Construction documents change regularly, it is not unusual for me to download hundreds of files in the morning, only to replace 50% of them later in the day. These files come from many different "Internet" sites depending on what system the client has chosen to use.
Emma1-N 3,230 Reputation points Microsoft External Staff Moderator

2026-01-24T07:17:34.16+00:00

Hi Graham Cooper,

Since you’ve already tried the available workaround steps but they still don’t fully address the issue, the best next step is to submit your feedback through Feedback Hub so the engineering team can review it and consider further improvements in future updates. Please refer to the Feedback Hub link provided in the answer above to submit your report.

Answer 4

Q&A Assist

AI generated content. This question contains an answer created with AI from Q&A Assist. Learn more

The provided context does not contain specific information regarding the release of a fix for the security changes implemented in update KB5066835. For the latest updates and fixes, I recommend checking the official Microsoft support channels or the Microsoft Knowledge Base for any announcements related to this update.

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When will Microsoft release a fix for the security changes implemented in update KB5066835

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