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SQL Server linked server connections stay open after Windows updates of 13 October 2026: Microsoft confirms issue, fix due

Microsoft says Windows updates since 13 October can leave SQL Server linked server connections open, slowing servers; an out-of-band fix is promised within days.

audiotale.net team

· 7 min read

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On this page
  1. Key points
  2. What to do
  3. What happened
  4. Which updates and versions
  5. Background
  6. How the failure shows up
  7. What it means
  8. What we don't know yet
  9. What to watch next
  10. Sources

Microsoft has confirmed that the Windows security updates it released on 13 October 2026, and every later update on top of them, can make SQL Server linked server queries leave their connections open. On a server that runs such queries all day, the open connections to Oracle, PostgreSQL and other external databases pile up until performance degrades. Microsoft has not shipped a fix yet: it says an out-of-band update will follow "in the next few days", and a mitigation is available now only through Microsoft Support for business.

Key points

  • Microsoft's Windows release health dashboard lists the issue as "SQL Server linked server connections might remain open", status Confirmed, opened on 11 November 2026 (15:11 PT).
  • It starts with the update of 13 October 2026 and applies to later updates too; affected servers keep connections to external databases open after the queries finish.
  • It affects linked server queries that use OLE DB providers; Microsoft names Oracle and PostgreSQL connections as known examples.
  • The temporary relief is to close idle connections by hand or restart the SQL Server service, but both can interrupt running queries and the problem can return.
  • The fix is promised as an out-of-band Windows update "in the next few days", with no date given.

What to do

  1. Check whether you are exposed. You are if a Windows machine runs SQL Server linked servers that reach another database through an OLE DB provider (the Oracle and PostgreSQL providers are the named cases) and has installed the 13 October 2026 update or any later one. Microsoft's own wording is "server devices", so the risk sits on the server side.
  2. Look for the symptom. On the external database, count sessions opened by your SQL Server host. A number that keeps rising even when no linked server query is running is the pattern Microsoft describes: "an increasing number of open connections to external databases, even when the associated SQL Server linked server queries are no longer running."
  3. Relieve the pressure. If you can identify idle connections, close them by hand. Restarting the SQL Server service also restores stability for a while. Microsoft warns that both steps can interrupt active queries or transactions, so pick a quiet window, and the problem can come back after enough operating time.
  4. Ask for the mitigation if you need it now. Microsoft says one exists for affected enterprise devices and is applied by contacting Microsoft Support for business. We do not know what it changes, because Microsoft has not published it.
  5. Do not uninstall security updates as a reflex. Microsoft has not recommended it, and the November updates carry other fixes (see our Patch Tuesday outlook). Watch the release health page and install the out-of-band update when it appears.

What happened

On 11 November 2026 Microsoft added a new known issue to the release health pages for most supported Windows versions. The entry says that after the Windows updates released on 13 October 2026 "and later" are installed on server devices, connections created by SQL Server linked server queries "might remain open after the queries complete". Microsoft continues: "As additional queries are performed, connections to external databases can accumulate instead of closing as expected. This can slow or degrade server performance after prolonged run time."

The problem is narrow in cause and wide in reach. It involves SQL Server linked server queries that use OLE DB providers to connect to external databases. Oracle and PostgreSQL are named as known cases, and Microsoft says they are "among those known to be affected", which leaves room for other providers. The entry does not name SQL Server versions, so the trigger appears to be on the Windows side rather than in a particular SQL Server build. That is our reading of the entry, and Microsoft has not said which Windows component changed.

BleepingComputer and The Register both reported the entry on 12 November. The Register expects the out-of-band fix within days; Microsoft's own text says only that it will update the documentation once the update is released.

Which updates and versions

Microsoft opened the issue separately on each platform's page, and the originating October update differs by platform. These are the ones we could read on the release health pages on 12 November:

Platform Originating update (13 October 2026)
Windows 11, version 26H1 KB5127646 (OS build 28000.3231)
Windows 11, versions 25H2 and 24H2 KB5127648 (OS builds 26200.9711 and 26100.9711)
Windows 11, version 23H2 KB5126653 (OS build 22631.7652)
Windows Server 2025 KB5126646 (OS build 26100.33650)
Windows Server 2022 KB5126655 (OS build 20348.5761)
Windows Server 2012 KB5126835

The affected-platform list in the entry is longer than that table. On the client side it names Windows 11 versions 26H1, 25H2, 24H2 and 23H2, Windows 10 version 1809 and Windows 10 Enterprise LTSC 2019. On the server side it names Windows Server 2025, 2022, version 1809, 2016, 2012 R2 and 2012. For the platforms missing from the table we could not open a release health page with the originating KB number, so check Microsoft's page for your version. The Register named KB5126646 as the update behind the change; that is the Windows Server 2025 update, and Microsoft's other pages list different numbers for other editions.

Background

This is not the only problem the October update cycle has caused. In October, the Windows Server update broke sign-in to Outlook on the web and mail sending on some on-premises Exchange servers. Microsoft's Windows Server 2025 page shows that issue as resolved on 10 November by KB5131080, and The Register covered the weekend admins lost to it. Also on 10 November, Microsoft marked resolved a USB audio problem that began with the 8 September update KB5124008; the fix is in KB5132061.

Linked servers are the SQL Server feature that lets one instance run queries against another database as if it were a table. They are used for reporting against Oracle, for gradual migrations to PostgreSQL, and for nightly jobs that join a local database to a remote one. Many of them sit in old code that nobody has touched for years, which is why a regression in connection handling is hard to spot and easy to blame on the remote database.

OLE DB is a Microsoft programming interface for reaching data sources, and linked servers use OLE DB providers to talk to other database products.

How the failure shows up

Connection leaks are slow. A linked server that runs a few queries an hour might hold a handful of extra connections by the end of a day, while one that runs thousands will reach a connection limit on the external side sooner. Microsoft's wording, "after prolonged run time", fits that pattern, and it is why the restart workaround "temporarily" fixes things and the issue "can resurface".

Where the damage appears depends on the remote database. Oracle and PostgreSQL both cap the number of simultaneous sessions, and each open session uses memory on the remote server. Microsoft's entry talks about slowdown and degraded performance, not about outages, and we did not find reports of data loss or corruption. Anyone who sees those symptoms should treat them as a separate problem.

What it means

For database administrators the main change is that the monitoring that matters is on the remote side. SQL Server's own view may look healthy, because the leftover connections are not tied to a query that is running. Counting sessions per client host on the Oracle or PostgreSQL side is the quickest way to tell.

For patch managers it is another case for a staged rollout. Microsoft's October updates reached production servers a month ago, and the confirmation came on 11 November, four weeks later. A leak that builds up over days is easy to miss in a short test, so a test ring is most useful when it includes one representative linked server job and someone watching its session count on the remote side.

For small organisations without a support contract, the mitigation is the sticking point. Microsoft says it is available to "affected enterprise devices" through Microsoft Support for business, and the out-of-band update should remove the need, but the date is open.

What we don't know yet

  • The release date and KB numbers of the out-of-band update. Microsoft says only "the next few days".
  • What the mitigation does and what it costs. Microsoft has not described it publicly.
  • Which OLE DB providers besides Oracle and PostgreSQL are affected. Microsoft says those two are "among those known".
  • Which SQL Server versions and which Windows component are involved. The entry names neither.
  • The originating KB numbers for Windows 10 version 1809, Windows 10 Enterprise LTSC 2019, Windows Server 2016 and Windows Server 2012 R2, which were not on pages we could open.

What to watch next

Watch the "Known issues" list on Microsoft's Windows release health page for your version; Microsoft says it will update the entry when the out-of-band update ships. When it does, check that the update replaces the October and November cumulative updates on your edition rather than stacking on top of them, apply it first on a test server that runs linked server jobs, and compare session counts on the remote database before and after. We will add a dated update to this article when Microsoft publishes the fix.

Sources

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