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Sql Server 2014 connectivity issue after Windows patch update

pdsqsql 436 Reputation points
2025-09-23T00:35:23.5033333+00:00

Hello,

We have currently Sql server 2014 SP1 and after our windows team apply the patch with GPO which caused connectivity issue within the application although I am able to connect via my local SSMS but when our application trying to connect it causing the issue and throwing following error:

Message=A connection was successfully established with the server, but then an error occurred during the login process. (provider: SSL Provider, error: 0 - An existing connection was forcibly closed by the remote host.),Source=Framework Microsoft SqlClient Data Provider,''Type=System.ComponentModel.Win32Exception,Message=An existing connection was forcibly closed by the remote host,Source=,'

We applied latest sql server SP3 and CU4 but still having an issue.

We compare another server which has similar Sql server version Sql 2014 with SP3 + CU4 and this sql server doesn't have any issue.

I thought TLS protocol having mis match but now updating to latest it should fix but doesn't help.

Any suggestion?

SQL Server Database Engine
Answer recommended by moderator
  1. Dinesh Yadlapalli 85 Reputation points Microsoft External Staff Moderator
    2025-10-17T13:27:18.3+00:00

    Hi @pdsqsql ,

    Thank you for reaching out to the SQL forum.

    Your issue seems to be related to TLS protocol support and the SQL Client driver used by your application. After a Windows patch via GPO, your application cannot connect to SQL Server 2014 SP3 + CU4.

    Please try below things to fix the issue.

    1. If you are using .NET Framework, ensure it's 4.6 or higher, as earlier versions do not support TLS 1.2 by default. For older .NET versions, you may need to explicitly enable TLS 1.2 in code.

    ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

    1. If your application uses System.Data.SqlClient, ensure it's updated to a version that supports TLS 1.2. If you are using ODBC or OLEDB, update the below drivers.

    ODBC Driver 17 for SQL Server

    OLE DB Driver for SQL Server

    1. Use a tool like IISCrypto or PowerShell to confirm TLS 1.2 is enabled and TLS 1.0/1.1 are disabled. Please check below Registry paths.

    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols

    1. Check registry settings, installed drivers, and .NET versions. Ensure both servers have identical TLS and driver configurations.
    2. Enable detailed logging to capture the exact driver and protocol being used during connection attempts.

    Please refer below link.

    https://support.microsoft.com/en-us/topic/kb4500181-cumulative-update-4-for-sql-server-2014-sp3-a55b2271-fdae-8e82-115c-05214cc8dac0

    I hope this information helps. Please do let us know if you have any further queries.

    Regards,

    Dinesh

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  1. Erland Sommarskog 133.6K Reputation points MVP Volunteer Moderator
    2025-09-25T20:47:05.39+00:00

    If you can connect to this instance from SSMS, this suggests that the application is using an outdated driver that uses TLS 1.0. Which you should not be using, so go and fix that application.

    I guess that the patch the Windows team applied disabled TLS 1.0 entirely. Given that TLS 1.2 has been there for ten years now, it's a about time.

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