Microsoft: Windows updates since October cause SQL Server connection leaks

Microsoft has acknowledged that Windows updates shipped from October 2026 Patch Tuesday onward are degrading the performance and stability of SQL Server, according to BleepingComputer. The company described the problem in an update posted to its Windows release health dashboard on Wednesday.

The root cause is linked server queries that fail to shut their connections once they finish. Rather than closing, those connections pile up, and the growing count gradually slows the server down.

Microsoft narrowed the fault to linked server queries that reach external databases through OLE DB providers. Connections to Oracle and PostgreSQL are among the ones confirmed to be hit, the company said.

Administrators in affected environments may notice that connections to outside databases keep climbing even after the linked server queries behind them have stopped running.

There are short-term options, but neither is clean. Admins can shut the leftover connections by hand or restart the SQL service to steady performance for a while, though doing so can terminate queries that are still active. The problem is also expected to return after a period, so restarting does not eliminate it.

Both client and server systems are caught up in the bug. That covers Windows 10 and Windows 11 on the desktop side, plus Windows Server 2012 and every later release. Microsoft said an out-of-band Windows update will arrive within the next few days to correct it.

In the meantime, IT teams can ask Microsoft Support for Business for a mitigation that holds the issue in check until the patch lands.

The disclosure follows other SQL Server trouble Microsoft has been tracking. In September it offered a stopgap measure for database crashes on certain Windows Server 2025 machines, which were tied to recent changes in how memory is managed. That fault appears when the Lock Pages in Memory policy is switched on and can produce crash dumps, services that stop or restart without warning, failed maintenance jobs, memory corruption errors and access violation exceptions carrying 0xC0000005 codes.

Separately, Microsoft confirmed on Tuesday that November 2026 security updates will not install on Windows 11 machines carrying the October preview update. Those users are reporting 0x80070306, 0x800f0989 or 0x800f0993 error codes.