Teams URL referrer suddenly changed

Good day @Nanos Nick (MPBSDP), and I appreciate the clear explanation of your concern.  

Just to gently clarify before we go any further, this is a user‑to‑user support forum. I don’t have the ability to access or investigate individual accounts because this is a user-to-user support forum. Moderators and contributors, including external Microsoft employees, do not have access to internal systems or the ability to directly take action on Microsoft product features. However, I truly hope I can help review your situation, offer some guidance, and support you in finding the right next steps as best as possible.   

Based on Microsoft 365 networking guidance, this behavior reflects Microsoft’s ongoing move to unify CDN delivery under the *.microsoft domain (including *.static.microsoft), so the issue likely occurred because your server still allowed older domains like *.teams.cdn.office.net while Teams has begun using the newer teams.public.onecdn.static.microsoft endpoint. 

Here are some options you may consider: 

Note: The steps below require support from your organization’s IT, network, or security admin. If you’re an end-user, please contact your admin and share this information with them. In case you do not know who is your IT admin, kindly refer to this article: How do I find my Microsoft 365 admin? - Microsoft Support  

Option 1: Immediate resolution 

To restore functionality quickly, the following steps can be applied: 

Add the domain below to your web server allow list: 

• https://teams.public.onecdn.static.microsoft/

Validate access again from Teams after applying the change. 

If your security policy allows, consider allowing a broader domain: *.static.microsoft 

This helps prevent similar disruptions caused by future CDN updates. 

Note: Allowing the wildcard domain is more resilient and aligned with Microsoft’s current endpoint guidance. 

Option 2: Long-term solution for stability 

To avoid similar issues in the future, it is recommended to automate endpoint updates: 

Use the Microsoft 365 IP Address and URL Web Service as the authoritative source. 

Set up a scheduled process to: 

Query the /version endpoint regularly (up to once per hour). 

Detect when a version change occurs. 

When a change is detected: 

Call the /changes endpoint. 

Review entries such as: 

• AddedUrl 
• AddedIpAndUrl 
• AddedSubstituteUrl 

Update your firewall, proxy, or web server allow list before the effective date. 

Note: Microsoft generally publishes changes up to 30 days in advance, but some urgent updates may be released outside the normal cycle. 

Additionally, I recommend a few ways to stay informed about upcoming changes: 

Subscribe to the Microsoft 365 endpoint RSS feed to get notified whenever endpoint data changes.  

Regularly check the Microsoft 365 Message Center for broader service updates or important changes that may require action. 

Additional information is available in the following resources: 
Managing Microsoft 365 endpoints - Microsoft 365 Enterprise | Microsoft Learn 

Microsoft 365 IP Address and URL web service - Microsoft 365 Enterprise | Microsoft Learn 

Microsoft 365 URLs and IP address ranges - Microsoft 365 Enterprise | Microsoft Learn 

I hope this information is helpful. If you have any questions or need further support, please don’t hesitate to reach out at any time. 

Thank you for your patience and understanding. 

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