SQL Server Security Updates, October 2026: Every Version Patched This Month

What Happened

On 13 October 2026, Microsoft released a coordinated batch of eight security updates covering SQL Server 2017, 2019, 2022, and 2025. Each supported version received both a GDR (General Distribution Release, for those on the base RTM branch) and a CU (Cumulative Update, for those already on the latest cumulative update track). If your SQL Server instances have not been patched since before this date, they are missing fixes for memory-corruption vulnerabilities, privilege-escalation risks, and denial-of-service conditions that Microsoft considers serious enough to patch across every supported version simultaneously.

This article consolidates all eight releases so you can quickly determine whether your instances are affected and what action to take.

Which Versions Are Affected

The table below is the fastest way to check whether you are already patched. Run the build check query in the next section, then compare your result against the Patched Build column.

What These Updates Fix

Across the eight releases, Microsoft documented between 15 and 27 individual fixes per package. The fixes cluster into five clear themes.

VDI and Backup Path Memory Safety

A flaw in the Virtual Device Interface (VDI) and SQL Writer backup paths allowed malformed size values to reach memory-handling code without validation, potentially causing out-of-bounds memory access. This affects any environment using third-party backup tools that communicate via VDI (most enterprise backup agents do). The fix introduces hardened arithmetic and transfer-size validation that rejects invalid requests before any memory operation occurs. This fix appears in the 2025 CU9, 2025 GDR, 2022 CU27, 2022 GDR packages.

Backup and Restore Metadata Privilege Escalation

An integer-handling weakness in backup and restore metadata processing could allow a local authenticated user to gain elevated privileges and cause the SQL Server service to stop responding. The fix adds strict bounds validation and safe size-calculation checks. This is a local privilege escalation, so it requires an existing login, but it is still a high-priority fix for multi-tenant or shared environments. This fix appears in the 2025 CU9, 2025 GDR, 2022 CU27, and 2022 GDR packages.

FILESTREAM Fragment Validation on Availability Group Replicas

Secondary replicas in an Availability Group were not validating the size of FILESTREAM fragments received from the primary. An oversized fragment could be accepted without rejection. The fix adds explicit size validation on the secondary before the fragment is processed. This affects any AG environment where FILESTREAM is enabled. The fix appears across all eight packages.

Machine Learning Services and Language Extensions Memory Vulnerabilities

Multiple memory-corruption and memory-disclosure vulnerabilities existed in the SQL Satellite protocol message-parsing logic used by Machine Learning Services and Language Extensions. These are fixed in the 2025, 2022, 2019, and 2017 packages. If you have Machine Learning Services or any Language Extension installed, this fix is directly relevant to you.

PolyBase Validation, External Data Sources, and Third-Party Components

Several fixes address PolyBase security validation during data processing, unexpected SQL Server process termination when working with external data sources, and an update to the third-party archive-extraction component used when installing external language and library packages. The archive-extraction component update (present in 2022 GDR, 2019 CU32, and 2019 GDR) is a supply-chain hygiene fix: even if you do not actively use external libraries, having an outdated extraction component is a latent risk.

Additional Fixes

The 2022 CU27 package also fixes information-disclosure and denial-of-service vulnerabilities triggered when the Database Engine reads a specially crafted Extended Events (.xel) file. The 2017 packages include security and reliability improvements for Queued Updating Subscriptions in Transactional Replication.

Why You Should Apply These

• Out-of-bounds memory access via backup agents is patched: any environment using VDI-based backup tools (Veeam, Commvault, Veritas, and similar) is exposed until the VDI fix is applied.
• Local privilege escalation through backup metadata is closed: a low-privileged SQL login could previously leverage this to disrupt the service or escalate access.
• AG secondary replicas will now reject malformed FILESTREAM fragments, reducing the risk of replica instability or data-integrity issues in FILESTREAM-enabled AG environments.
• Machine Learning Services memory vulnerabilities are resolved: memory-corruption and disclosure bugs in the SQL Satellite protocol are fixed across all versions that ship ML Services.
• PolyBase and external data source crashes are addressed: if your instances have experienced unexpected termination when querying external data sources, this batch likely contains the fix.
• Extended Events file parsing is hardened (SQL Server 2022): a crafted .xel file could previously trigger information disclosure or a denial of service during routine XE session review.
• Transactional Replication with Queued Updating Subscriptions is more reliable (SQL Server 2017): security and reliability improvements reduce risk in this replication topology.

Known Issues to Be Aware Of

Linked Server Queries via MSDASQL Fail with Error 7416

Affects: All eight packages in this batch.

Trigger: Any linked server query that routes through the MSDASQL (Microsoft OLE DB Provider for ODBC Drivers) provider.

Symptom: The query fails with error 7416. This is not a transient error; it will fail consistently after the patch is applied.

Should this delay deployment? If your environment relies on MSDASQL-based linked servers in production workflows, you should test thoroughly in a non-production environment before rolling out broadly. Check whether a workaround or hotfix is available in the KB article for your specific package before scheduling production deployment. If MSDASQL linked servers are not in use, this issue does not apply to you.

Access Violation Querying sys.dm_exec_requests During Database Recovery

Affects: SQL Server 2025 RTM CU9 (KB5126967) and SQL Server 2022 RTM CU27 (KB5126934) only.

Trigger: Querying sys.dm_exec_requests while a database is in the recovery phase (for example, immediately after a service restart or failover).

Symptom: An access violation may occur.

Should this delay deployment? This is a narrow timing window. If your monitoring or application code queries sys.dm_exec_requests continuously during startup, be aware of this issue. Check the relevant KB article for any available workaround before applying to CU-track instances.

Does This Affect You? How to Check

Check Your Current Build

SELECT
    SERVERPROPERTY('ProductVersion') AS Build,
    SERVERPROPERTY('ProductLevel')   AS Level,
    SERVERPROPERTY('ProductUpdateLevel') AS CULevel;

Compare the Build value against the Patched Build column in the version table above. If your build number is lower than the patched build for your branch, you are unpatched.

Check Whether VDI Backup Fixes Apply

If you use a third-party backup agent, VDI is almost certainly in use. Check whether SQL Writer is running:

-- On the host OS, run from a command prompt (not T-SQL):
-- sc query SQLWriter
-- A RUNNING state means SQL Writer is active and the VDI path is in use.

For the T-SQL side, confirm backup history exists from a non-native tool by reviewing msdb.dbo.backupset and checking the software_name column for third-party agent names.

Check Whether FILESTREAM Is Enabled (AG Environments)

-- Check whether FILESTREAM is enabled at the instance level
SELECT SERVERPROPERTY('FilestreamEffectiveLevel') AS FilestreamLevel;
-- 0 = disabled, 1 or higher = enabled

-- Check whether any databases use FILESTREAM filegroups
SELECT name, is_read_only
FROM sys.databases
WHERE database_id IN (
    SELECT database_id
    FROM sys.master_files
    WHERE type_desc = 'FILESTREAM'
);

If FILESTREAM is enabled and you have Availability Groups, the AG replica fix is directly relevant.

Check Whether Machine Learning Services or Language Extensions Are Installed

SELECT name, is_installed
FROM sys.dm_server_registry
WHERE registry_key LIKE '%MSSQLServer%'
-- This approach varies by version; the most reliable check is:
-- In SSMS, navigate to: Server Properties > Advanced > Miscellaneous
-- Or check Windows Programs and Features for 'Machine Learning Services'

Alternatively, check whether the Launchpad service is running on the host, as it is the entry point for all ML Services and Language Extension workloads.

Check Whether MSDASQL Linked Servers Exist

SELECT name, product, provider, data_source
FROM sys.servers
WHERE is_linked = 1
  AND provider = 'MSDASQL';

If this returns any rows, review the known issue before deploying to that instance.

Check Whether PolyBase Is Enabled

SELECT value_in_use
FROM sys.configurations
WHERE name = 'polybase enabled';
-- 1 = enabled

How to Apply

1. Check your current build using the query above and confirm which package applies to your branch (GDR or CU).
2. Download from the Microsoft Download Center or Update Catalog using the KB links in the version table.
3. Apply to a non-production environment first and run your standard regression and smoke tests, paying particular attention to any MSDASQL linked server queries.
4. Take a full backup of all user databases and the system databases before patching production.
5. Plan for a service restart: all SQL Server patches require a restart of the SQL Server service. Schedule a maintenance window accordingly.
6. Verify the build number after patching by re-running the build check query and confirming it matches the patched build in the table.
7. Review the KB article for your specific package for any additional post-installation steps or workarounds for known issues.

If You Are on an Unsupported Version

SQL Server 2016 reached end of extended support in July 2026. SQL Server 2014 and earlier have been out of support for longer. None of these versions receive fixes from this batch or any future batch. The vulnerabilities addressed here, including the VDI memory-access issue and the privilege-escalation bug in backup metadata processing, remain permanently unpatched on those versions. If you are still running SQL Server 2016 or earlier, the practical risk from unpatched security vulnerabilities increases with every monthly release cycle. Migration to a supported version should be treated as an urgent project, not a future consideration.

Key Takeaways

• Eight packages, four versions, one date: all fixes landed on 13 October 2026 and every supported SQL Server version is covered.
• The VDI backup path and backup metadata fixes are the highest-priority items for most production environments, given their potential for memory-access violations and local privilege escalation.
• FILESTREAM users with Availability Groups should prioritise patching, as the secondary-replica fragment-validation fix directly reduces data-integrity risk.
• The MSDASQL linked server known issue affects all eight packages: test before deploying to any instance that uses MSDASQL-based linked servers.
• Unsupported versions receive nothing: if you are on SQL Server 2016 or earlier, these vulnerabilities will not be fixed for you.

DBA Services Recommendation

For organisations on a DBA Services managed services agreement, our team has already reviewed this patch batch, assessed applicability against your registered instance inventory, and will be scheduling deployment through your agreed maintenance windows. You do not need to action this yourself. If you are not yet a managed client and would like assistance evaluating or deploying these updates, contact us to discuss how we can help.