A new cumulative update (October 2025 CU) has been released for Office Online Server.
OOS Build: 16.0.10417.20059
Important before installation:
Updating Office Online Server requires removing the server from its farm and then recreating the farm or joining the updated farm. Follow the instructions in How to update Office Online Server.
Office Online Server CU – KB article describing the CU:
Office Online Server CU – CU download link:
Important notes
Note for this CU:
Installing this security update requires the release version of Microsoft Office Online Server.
Included fixes and improvements
Office Online Server
This update fixes Excel vulnerabilities that can allow remote code execution or disclosure of information. Microsoft lists the following security advisories: