Resolved: SharePoint Worker Process Crashes with 0xC0000409 Exception

Introduction

We'll address a common issue encountered after applying the September 2025 Cumulative Update (CU) for SharePoint Server Subscription Edition: application pool worker process crashes with the exception code 0xC0000409. This article provides a step-by-step guide to understanding and resolving this error.

Root Cause

Following the September 2025 CU, the SharePoint Server application pool worker process may crash with the exception code 0xC0000409. The event log will contain entries similar to the following:

Faulting application name: w3wp.exe, version: 10.0.17763.1, time stamp: 0xcfdb13d8
Faulting module name: owssvr.dll, version: 16.0.19127.20100, time stamp: 0x689cd397
Exception code: 0xc0000409
Fault offset: 0x000000000033b39b
Faulting process id: 0x32fc

Resolution

To resolve this issue, follow these steps:

• Ensure the latest Cumulative Update (CU) is installed on your SharePoint servers.
• If the issue persists, verify that you are using the most recent version of the owssvr.dll module.
• If necessary, rerun the SharePoint configuration wizard.
• If you are still experiencing issues, contact Microsoft Support.

Additional Information

This issue is often caused by a faulty or incompatible owssvr.dll module. By installing the latest update packages and ensuring the correct version of the module, you can resolve this issue.