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Microsoft Windows HTTP.sys and IIS localhost HTTP/2 disruption after recent updates

Service Disruption
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1 unique sources, 1 articles

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Microsoft fixed a known issue that broke HTTP/2 localhost (127.0.0.1) connections and IIS websites on affected Windows systems, disrupting local apps and web services. The bug affected Windows 11 and Windows Server 2025 users and produced ERR_CONNECTION_RESET and ERR_HTTP2_PROTOCOL_ERROR failures. Microsoft tied the problem to HTTP.sys and said it could appear after recent updates, restarts, and connectivity changes. Many devices were remediated with Known Issue Rollback (KIR), while enterprise systems still need a policy-based workaround until a future Windows update ships.

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Timeline

  1. 17.10.2025 16:58 2 articles · 7mo ago

    Microsoft mitigates localhost HTTP/2 regression on Windows

    Mitigation Patch Update

    Microsoft fixed a known issue in Windows 11 and Windows Server 2025 where recent Windows security updates caused HTTP/2 localhost (127.0.0.1) connection resets and IIS website failures, producing ERR_CONNECTION_RESET and ERR_HTTP2_PROTOCOL_ERROR for apps and services that rely on HTTP.sys and ASP.NET Core. Windows users had reported failures on Stack Exchange, Reddit, and Microsoft forums, and Microsoft linked the problem to HTTP.sys, recommended checking for updates and restarting impacted devices, automatically resolved many non-managed business and home devices through Known Issue Rollback (KIR), and directed enterprise-managed Windows 11 24H2, Windows 11 25H2, and Windows Server 2025 systems to install the KIR group policy until a future Windows update ships.

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