Windows Updates Disrupt SQL Server Connections and Stability

By Amara Osei

Microsoft confirmed on Wednesday that Windows updates released since the October 2026 Patch Tuesday are causing SQL Server performance and stability issues across client and server Windows systems.

Microsoft’s Windows release health dashboard attributes the main performance fault to server queries that finish without closing their connections. The abandoned connections accumulate, so degradation emerges over time rather than at the instant a single query completes. That makes connection counts a lasting signal even when the workload appears to have stopped.

What is causing SQL Server to slow down?

Microsoft explained: “This issue affects SQL Server linked server queries that use OLE DB providers to connect to external databases. Oracle and PostgreSQL connections are among those known to be affected.”

The fault sits in the path between SQL Server and an external database. A linked-server query using an OLE DB provider completes its work, but the associated external connection remains open.

Microsoft added: “In affected environments, administrators might observe an increasing number of open connections to external databases, even when the associated SQL Server linked server queries are no longer running.”

As those connections build up, they degrade server performance. The visible symptom is a rising external-connection count after query activity has ended, not an immediate failure tied to one request.

Administrators may be able to manually close connections left open by the bug or restart the SQL Server service for temporary relief. A restart may also terminate active queries, and the problem can return after some time because those measures do not remove the underlying defect. Microsoft Support for Business can provide a mitigation until the fix is available.

Takeaway: SQL Server performance declines as completed linked-server queries leave external connections open and the number keeps rising.

Which Windows systems does the issue cover?

Microsoft said the issue reaches both client systems on Windows 10 and Windows 11 and server systems running Windows Server 2012 or later. The stated scope therefore spans two named Windows client releases and a server range that begins with the 2012 edition.

Microsoft says an out-of-band Windows update will be released over the next few days to fix the issue. Administrators can contact Microsoft Support for Business for a mitigation until then. The out-of-band release is the stated fix, while manual connection closures, service restarts and support measures address the problem only temporarily.

Takeaway: The affected footprint covers Windows 10, Windows 11 and Windows Server 2012 onward, with an out-of-band fix due within days.

What other Windows failures need attention?

Microsoft has also documented a separate SQL Server crash problem on some Windows Server 2025 systems. In September, the company shared a temporary workaround for crashes that it linked to recent memory management changes. The fault appears when administrators enable the Windows Lock Pages in Memory, or LPIM, policy.

Microsoft lists five possible outcomes under that condition:

• SQL Server crash dumps;
• SQL Server services that stop or restart unexpectedly;
• failures during database maintenance operations;
• memory corruption errors; and
• access violation exceptions carrying the 0xC0000005 error code.

The September workaround remains temporary. This crash path differs from the linked-server connection leak because it depends on LPIM rather than the external-query connection lifecycle. Microsoft has issued a temporary workaround for the crash path, while its support mitigation for the connection problem remains available until the out-of-band fix.

Microsoft also confirmed yesterday that the November 2026 security updates are failing to deploy on Windows 11 systems that installed the October preview update. Affected users encounter one of three reported error codes:

• 0x80070306
• 0x800f0989
• 0x800f0993

The deployment failure blocks the November security update in Windows 11 environments carrying the October preview. That creates a third operational issue, alongside the SQL Server connection leak and the Windows Server 2025 crash condition. For security administrators, the three listed codes distinguish the failed November deployment from the separate 0xC0000005 crash signature on Windows Server.

Takeaway: The Microsoft maintenance burden has three parts: a linked-server connection leak, an LPIM-linked crash condition and a Windows 11 update-deployment failure.

Microsoft’s out-of-band release is the stated route to resolve the connection problem; support mitigations and service restarts provide only temporary relief.