HTTP requests in .NET applications fail after Windows update.

Fault phenomenon

After a routine Windows system update, all .NET-based applications (including C# console, Web API, etc.) were unable to send HTTP requests, but the problem disappeared automatically after a system restart.

Root cause analysis

Based on community experience and analysis of Microsoft's official documentation, the root cause of the problem lies in the fact that the Windows update process modifies the underlying libraries that the system's network components and the .NET runtime depend on, but the related services or components fail to complete the initialization or refresh correctly.

Key factors that may be involved

1. The HTTP.sys or WinHTTP configuration has not been refreshed.

• HTTP.sysThe core of the Windows HTTP stack (used for IIS, HttpListener, etc.)
• WinHTTPUsed by many applications (including older versions of .NET HttpWebRequest).
• Problem manifestationThe update process replaced component files or registry configurations, but did not immediately restart dependent services.
• as a result of: A conflict between old and new configurations or DLL versions causes a .NET application to get stuck in an error state when making a request.

2. Inconsistent SSL/TLS states

• Schannel UpdateWindows updates frequently update the security channel (for SSL/TLS).
• .NET runtime cache.NET maintains its own SSL/TLS session cache.
• Conflict outcomeAfter the underlying Schannel DLL is updated, the .NET runtime's internal state still points to the old module, causing HTTPS connection establishment to fail or hang indefinitely.

3. Network stack initialization issues

• Network SubsystemThis includes the TCP/IP protocol stack, port pool, etc.
• Status after updateA full reboot is required to reinitialize.
• Phenomenon ContradictionsBasic functions (such as ICMP ping) work normally, but advanced features used by the .NET BCL are in a "frozen" state.

Solution

Resolve immediately

• Completely restart your computer - Clear all network kernel objects and initialize from scratch.

Preventive measures

• Schedule a system restart after a planned Windows update.
• Monitor the network connectivity status of .NET applications after a system update.
• Consider implementing a network connectivity health check mechanism in your application.

Summarize

System reboot is the most thorough way to resolve such issues, ensuring that all network components and runtime environment complete a full reinitialization process.