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CosmosDB emulator not responding

Arkadii Hryshko 46 Reputation points Microsoft Employee
2025-10-15T21:20:25.6266667+00:00

After last windows update(2025-10 Cumulative Update for Windows 11, version 25H2 for x64-based Systems (KB5066835) (26200.6899) emulator not working.
Started without any errors, but opened page is unreachable:

User's image

Reproduced on couple machines.

Tried steps from tutorial, but did not work.

Azure Cosmos DB
Azure Cosmos DB

An Azure NoSQL database service for app development.

Answer recommended by moderator
  1. Arkadii Hryshko 46 Reputation points Microsoft Employee
    2025-10-22T18:48:49.4366667+00:00

    All working after installing the latest Windows Security update https://www.microsoft.com/en-us/wdsi/defenderupdates

    In case it won`t help try to reinstall the emulator as well with latest version.

    1 person found this answer helpful.
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  1. Manu Poruthoor 15 Reputation points Microsoft Employee
    2025-10-16T16:32:14.84+00:00

    It appears my issue has been solved after uninstalling the security update that came with the recent cumulative update. After uninstalling, this is my security update version:User's image Unfortunately, this looks like a temporary fix because security fixes are required for us.
    User's image

    2 people found this answer helpful.
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  2. Anonymous
    2025-10-22T15:53:09.52+00:00

    Hi Arkadii Hryshko,
    Please try the steps below. If these don’t resolve the issue, kindly share your observations for further investigation

    1. Windows Update → Check for updates → install anything pending → reboot.
    2. If it still fails, disable HTTP/2 (run as Administrator), then reboot:
    reg add "HKLM\SYSTEM\CurrentControlSet\Services\HTTP\Parameters" /v EnableHttp2Tls /t REG_DWORD /d 0 /f
reg add "HKLM\SYSTEM\CurrentControlSet\Services\HTTP\Parameters" /v EnableHttp2Cleartext /t REG_DWORD /d 0 /f
    1. Verify: open https://localhost:8081/_explorer/index.html.

    1 person found this answer helpful.

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