mdnsNSP.dll - This module is blocked from loading into the Local Security Authority

Short summary on this one as problem still exists: Since Local Security Authority (LSA) protection is on per default starting with Windows 11 24H2, this prompt will appear. Bonjour might be installed through iTunes or other third-party software (like Printix that simulates AirPrint). Only fix so far, is an uninstallation (if not needed any more). If needed, there is no solution. Also, Microsoft does not offer policies to define exclusions. Turning of LSA can't be seen as acceptable solution.

In the end, Apple needs to fix their Bonjour DLL. Currently, it is not fulfilling the requirements defined by Microsoft like "digitally signed with a Microsoft signature": Configure added LSA protection | Microsoft Learn

I had the exact same issue (on Windows 11), and it was a real headache. I couldn’t resolve the problem despite trying everything—reinstalling iTunes, updating, cleaning the system and registry, installing the Windows Store version, the desktop version, older versions, etc. Nothing worked.

Finally, I found a working solution:

• Uninstall the Bonjour service (no need to uninstall iTunes if you already have the latest version): Go to Control Panel > Programs and Features or Settings > Installed Apps > Locate and uninstall Bonjour.
• Download Bonjour manually from the official Apple site:

Download Bonjour Print Services for Windows v2.0.2 - Apple Support

• Reboot your system.

That worked for me — while all other solutions failed.

uninstalled itunes and bonjour, and got itunes from the apple website instead, warning has gone and itunes now recognizes phone, so all good. GL to you.

Yes, adding "mdnsNSP.dll" under this registry key activates Bonjour as Security Package and allows access to the Local Security Authority what removes the security warning: Restrictions around Registering and Installing a Security Package - Win32 apps | Microsoft Learn

Downside: This gives the DLL the ability to access access plaintext passwords of authenticated users. This mechanism is commonly exploited for credential theft. From my point of view, giving the "old" Bonjour DLL such high privileges creates a bad gut feeling and can be seen as security risk.

Do you use AirPlay or sync over Wi-Fi? If not then I don't think you need Bonjour at all.

tt2

Also played around with Bonjour as separate installer. The current version is 3.1.0.1 from 2015 (extracted from iTunes installer). Also found: Download Bonjour Print Services for Windows v2.0.2 - Apple Support which gives you an even older version...

Updates to and reinstallation of version 3.1.0.1 do not fix the LSA warning.

My summary: Uninstall Bonjour (if not needed) or hope to get an updated version.

If mdnsnsp.dll is being blocked, you can add it back manually:

1. In Regedit, go to: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa
2. Find Security Packages and double-click it.
3. In the list that appears, add a new entry: mdnsnsp.dll
4. Click OK, close Regedit, and restart your PC.

Worked for me, anyway.

If mdnsnsp.dll is being blocked, you can add it back manually:

In Regedit, go to: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa

Find Security Packages and double-click it.

In the list that appears, add a new entry: mdnsnsp.dll

Click OK, close Regedit, and restart your PC.

Worked for me, anyway.

FWIW : here is what happened to me. I had NO current Apple products or software installed on my freshly built Windows 11 PC. Or so I thought. Got the Bonjour mdndnsp.dll blocking message as well (right after the 24H2 installatione). Turned out to be a Spotify plugin that was causing this behaviour on mine. Went to the installed apps and sure enought, somehow Bonjour was installed with Spotify? Just my 2cts if anyone (like me) was wondering what an Apple service was doing on my kit.

Here is a solution to disable the warning:

https://community.rsa.com/s/article/RSA-MFA-Agent-2-3-4-DLL-error-on-Windows-11-24H2

Resolution

RSA Engineering is working on a solution and will provide updates soon. In the meantime, we recommend avoiding the upgrade to Windows 11 24H2 patch until RSA provides an update.

In case the Windows machine is already updated to Windows 11 24H2, follow the steps below to disable Local Security Authority (LSA) and restore MFA agent functionality.

Workaround

Disable Local Security Authority (LSA)

Steps to disable using Local Group Policy on Windows 11 version 24H2 and later:

1. Open the Local Group Policy Editor by entering gpedit.msc.
2. Expand Computer Configuration > Administrative Templates > System > Local Security Authority.
3. Open the Configure LSASS to run as a protected process policy.
4. Set the policy to Disable.
5. Restart the machine 

I reverted the regedit change to how it was blank and uninstalled bonjour. Thank you for the heads up!

This is a user-to-user forum. No one here (with VERY limited exceptions) works for Apple If you want Apple to listen, use this link:

Product Feedback - Apple

Also see:

Security implications of Bonjour protocol for developers and administrators - Apple Support

Yes, uninstall iTunes and reinstall, then remove bonjour from Settings - Apps - Installed Apps and you'll find Bonjour. I used the registry method in a previous post and it fixed it for me and kept bonjour.