MS Defender setting

Hello!

Your English is perfectly fine - I understand your question clearly.

Unfortunately, you cannot customize the block page that Microsoft Defender for Endpoint displays when a URL indicator is triggered. This is a limitation of the platform.

What You See vs. What You Can Control

When Defender blocks a URL based on your indicator:

• Desktop browsers: Users see a generic browser error (connection reset/refused) or the browser's standard block page
• Microsoft Edge with SmartScreen: May show a Microsoft warning page, but this cannot be customized
• The exact appearance depends on the browser and how the block is enforced

What you CAN control:

• The action (Alert, Block, Allow, Warn)
• Alert severity and description in the Security Center
• Email notifications to your security team

What you CANNOT control:

• The block page appearance
• Custom messages to end users
• Branding or instructions on the block page

Workarounds and Alternatives

1. Use Network Layer Solutions

For customizable block pages, you'd need:

• Web proxy/gateway (like Zscaler, Cisco Umbrella, Forcepoint)
• Firewall with web filtering (Palo Alto, Fortinet)
• Network content filter that allows custom HTML block pages

These can be configured alongside Defender for Endpoint.

2. Communicate Through Other Channels

Since you can't customize the block page:

• Send email notifications when alerts trigger
• Create pop-up notifications via Intune or Group Policy
• Add instructions to your internal documentation/help desk
• Use Toast notifications on Windows to inform users

Example using Intune to send a notification:

powershell

# Custom script to show notification when specific event occurs # Deploy via Intune $title = "Website Blocked" $message = "This website is blocked by company policy. Contact IT if you need access." New-BurntToastNotification -Text $title, $message

3. Use Warn Instead of Block

If you select "Warn" instead of "Block" for your indicator:

• Users see a warning but can choose to proceed
• Microsoft's default warning page appears (still not customizable, but provides more context than a block)
• You still get alerts in the Security Center

4. Combine with Attack Surface Reduction Rules

You can use ASR rules alongside indicators, but these also don't offer custom messages to users.

What Your Users Will Actually See

Depending on the browser:

Microsoft Edge:

• May show SmartScreen warning: "This site has been reported as unsafe"
• Generic message from Microsoft

Chrome/Firefox:

• Usually just "Connection was reset" or "Unable to connect"
• No helpful message unless you have a proxy/filter

Internet Explorer (legacy):

• "This page can't be displayed"

Best Practice Recommendation

Since customization isn't available in Defender for Endpoint indicators:

1. Document your blocked URLs in an internal wiki/SharePoint
2. Train users on what the different block messages mean
3. Set up automated emails to notify users when their activity triggers an alert
4. Create a help desk article explaining blocked sites policy
5. Consider implementing a web proxy if custom messaging is critical for your organization

Alternative: Microsoft Defender Application Guard

If you want more controlled browsing with better user messaging, consider:

• Microsoft Defender Application Guard - Opens risky sites in isolated container
• Conditional Access policies - Can show custom messages before access

But these serve different purposes than URL indicators.

In summary: No, you cannot customize the block page for URL indicators in Microsoft Defender for Endpoint. This is a common request, but Microsoft hasn't provided this capability. You'll need to use other communication methods or consider additional web filtering solutions if custom block pages are important for your organization.

Thanks,

Jovan S.