Redazione RHC : 18 October 2025 08:30
The October updates for Windows 11 broke localhost functionality, preventing applications connecting to 127.0.0.1 over HTTP/2 from working properly.
While developers typically use localhost to test websites and debug applications, it can also be used by applications that need to connect to a locally running service to perform actions or requests.
After installing Windows 11 update KB5066835 and the September Preview Update KB5065789 , users found that applications were no longer able to complete HTTP connections to the localhost IP address (127.0.0.1). When they attempted to connect, they received errors such as “ERR_CONNECTION_RESET” or ” ERR_HTTP2_PROTOCOL_ERROR.”
The issue has been reported on Microsoft forums , Stack Exchange , and Reddit . All affected users report being unable to establish HTTP connections to 127.0.0.1.
The issue affected many popular applications, including debugging in Visual Studio, SSMS Login ID authentication, and the Duo desktop app, which checks the device’s security status and requests connection to web servers running on localhost.
“After installing the Windows 11 24H2 and 25H2 updates, you may experience an issue where Duo Prompt fails to sign in to Duo Desktop,” the Duo support bulletin states. “This may prevent authentication (or result in limited functionality) in situations where trusted endpoints, policies such as Duo Desktop and device health, Duo Desktop as an authentication method, Duo Passport, Duo Push verified with Bluetooth Autofill, or proximity verification are used.”
The BornCity blog suggests making the following registry changes, which supposedly can help resolve the issue by disabling the HTTP/2 protocol:
[HKEY_LOCAL_MACHINESystemCurrentControlSetServicesHTTPParameters] "EnableHttp2Tls"=dword:00000000 "EnableHttp2Cleartext"=dword:00000000Another method that some users find effective is installing the latest antivirus signature update for Microsoft Defender. However, others report that this doesn’t solve the problem.
As a result, the only reliable way to resolve the error is currently to uninstall the October update KB5066835 and the September preview update KB5065789.
After uninstalling them and restarting Windows, the loopback interface should allow HTTP/2 connections again, fixing the application issues.
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