Many Windows 11 users are facing a new problem after installing Microsoft’s October 2025 updates. The updates appear to have broken the localhost function, which is used by many apps and developers to connect back to their own computer using the address 127.0.0.1.
After installing the latest updates, KB5066835 from October and KB5065789 from September, users noticed that apps could no longer make HTTP/2 connections to localhost. When trying to connect, they see error messages such as “ERR_CONNECTION_RESET” or “ERR_HTTP2_PROTOCOL_ERROR.” This issue has been widely reported on Microsoft forums, Stack Exchange, and Reddit.
Localhost is an important part of how software developers test websites or run apps that communicate with local services. When it stops working, many programs that rely on it simply fail. Some of the most affected tools are Visual Studio, SQL Server Management Studio (SSMS) with Entra ID authentication, and the Duo Desktop app. Duo Desktop, for example, uses localhost connections to check the device’s security status and help users sign in safely.
According to a support note from Duo, the issue began after the recent Windows 11 updates. It can prevent the Duo Prompt from talking to Duo Desktop, which may block authentication or limit some features like Trusted Endpoints, Duo Passport, and Verified Duo Push with Bluetooth or Proximity verification.
A few users and tech experts have found temporary fixes. The website BornCity suggested that disabling HTTP/2 through the Windows Registry might solve the problem. To try this, you can add the following values to the registry:
[HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\HTTP\Parameters]
"EnableHttp2Tls"=dword:00000000
"EnableHttp2Cleartext"=dword:00000000
Some users also said that updating Microsoft Defender’s intelligence database helped, but others reported that it did not make a difference. For now, the only guaranteed way to fix the problem is to uninstall the recent updates completely. This can be done by running these commands in Command Prompt as an administrator:
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wusa /uninstall /kb:5066835
wusa /uninstall /kb:5065789
After removing the updates and restarting the computer, localhost connections should start working again. Microsoft has not yet commented on the issue, but many users hope the company will release a patch soon to fix it permanently.
