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SQL Server 2025 CU9 + GDR SQL Server 2025 CU9 + GDR Security update
Patch Tuesday

KB5126967

KB5126967: Security update for SQL Server 2025, CU branch, October 2026. Backup and PolyBase flaws fixed; recovery queries can crash

In short

Security fixes cover SQL Server components used for backup, PolyBase, and replication. Queries during database recovery can still trigger an access violation; a trace-flag mitigation is available.

Does it affect you? Applies to: SQL Server 2025 on Windows or Linux, all editions. The package is for x64 systems.

Build
17.0.5015.4
Servicing branch
CU
Security
24 fixed
Restart
Required
Review notes Additional details from the official release notes (2) Read notes
  • What changes The fix rejects oversized FILESTREAM fragments on Availability Group secondary replicas; the official page does not describe them as backup fragments.
  • What changes The update changes shared-memory handling in PolyBase. The official page does not specify data sharing or external data tools.

The official sources are linked at the end of the page.

For servers on the CU branch: they install cumulative updates, which also bring fixes beyond security. Servers on the GDR branch (security fixes only) get a separate update. Which branch am I on?

What changes

Fixes 17 changes

Backup Restore

6 items
  • Invalid size values in some backup requests are rejected before they can cause unsafe memory access.1
    Adds hardened arithmetic and transfer-sized validation to SQL Server Virtual Device Interface (VDI) and SQL Writer backup paths.
  • Malformed backup metadata can no longer use unsafe sizes that could raise privileges or stop a service.2
    Adds strict bounds validation and safe size calculations to SQL Server backup and restore metadata processing.
  • A flaw that could corrupt memory while opening a virtual backup device is fixed.4
    Fixes an out-of-bounds write vulnerability in SQL Server VDI when opening a virtual device set.
  • A flaw that could read or change memory during backup or restore is fixed.5
    Fixes an out-of-bounds read or write vulnerability in SQL Server VDI while processing transferred data during backup or restore.
  • Invalid size values in some backup requests are rejected before they can cause unsafe memory access.8
    Adds hardened arithmetic and transfer-sized validation to SQL Server VDI and SQL Writer backup paths.
  • Malformed backup metadata can no longer use unsafe sizes that could raise privileges or stop a service.9
    Adds strict bounds validation and safe size calculations to SQL Server backup and restore metadata processing.

PolyBase

3 items
  • SQL Server is less likely to stop unexpectedly while working with data outside the database.3
    Addresses unexpected SQL Server process termination while working with external data sources through PolyBase.
  • PolyBase checks data more carefully to fix a security flaw.6
    Resolves a PolyBase security vulnerability by improving validation during data processing.
  • Malformed data in PolyBase rollback records is now rejected.7
    Fixes unsafe deserialization of PolyBase rollback queue data so malformed payloads are rejected.

Extensibility

2 items
  • Memory flaws in the tools for machine-learning and language features are fixed.10
    Fixes multiple memory-corruption and memory-disclosure vulnerabilities in SQL Satellite protocol message parsing used by Machine Learning Services and Language Extensions.
  • Invalid settings for AI-generated text embeddings no longer cause unsafe memory reads.11
    Fixes an invalid memory-read vulnerability in the AI_GENERATE_EMBEDDINGS runtime parameter processing.

Distributed Query

  • Some linked-database connections work when the connection string has no user ID.12
    Fixes MSDASQL-linked server connections that fail when the provider string does not include a user ID (UID).

Replication

4 items
  • Merge data sync no longer overflows a buffer when it processes more than 250 web-sync entries.13
    Fixes a buffer overflow when merge replication processes more than 250 WebSync XML nickname entries.
  • A data-checking problem in replication operations is fixed.14
    Fixes an issue in replication operations that affects data validation.
  • A data-checking problem in merge updates is fixed.15
    Fixes an issue in merge replication Web Synchronization operations that affects data validation.
  • A problem processing input for change event streaming is fixed.16
    Fixes an issue in input data processing for change event streaming.

Programmability

  • Malformed trace records can no longer trigger unsafe memory reads.17
    Limits LoginSid processing within the SQL Trace reader to the internal buffer size to prevent out-of-bounds reads from malformed trace data.

Improvements 8 changes

High Availability and Disaster Recovery

  • Oversized backup fragments on secondary database copies are rejected.18
    Adds validation of FILESTREAM fragment size on Availability Group secondary replicas.

PolyBase

2 items
  • Incoming changes to a table are checked against its expected layout.19
    Adds validation for the delta table schema in PolyBase.
  • Data sharing with external data tools uses updated memory handling.20
    Updates shared memory handling in PolyBase.

Extensibility

  • Package extraction uses an updated component when external language or library packages are installed.21
    Updates the third-party archive-extraction component used by SQL Server when external language and external library packages are installed.

Replication

4 items
  • Replication security checks are more reliable when a Subscriber database is restored or upgraded.22
    Improves security and reliability in replication security metadata handling during Subscriber database restore and upgrade.
  • The Log Reader Agent is more secure and reliable in some replication setups.23
    Improves security and reliability for the Log Reader Agent in a heterogeneous transactional replication scenario.
  • Change feed settings are more secure and reliable.24
    Improves security and reliability for the change feed configuration.
  • Some replication operations check access more carefully to prevent unintended exposure of database information.25
    Strengthens authorization checks for certain replication-related database operations.

Known issues

  1. Open Affects: Not stated by the source

    Linked server queries that use MSDASQL fail with error 7416

    Linked-server queries that use the MSDASQL provider and specify a provider string might fail with error 7416. SQL Server can reject some configurations that worked in earlier builds.26

    Workaround status No workaround yet

    Microsoft has not published a manual workaround for this issue yet. Monitor release health until a resolving update is available.

  2. Open Affects: Not stated by the source

    Access violation when you query sys.dm_exec_requests during database recovery

    Queries against sys.dm_exec_requests might cause an access violation and create a dump file while a database is recovering. This can happen during restore, startup recovery, or before an availability group replica comes online.27

    How to apply the workaround SQL Trace Flag

    Use trace flag 4696 to opt out of the change, avoid querying databases that are recovering, or uninstall the update. The trace flag might cause monitoring queries on secondary replicas to return errors 976 or 978.27

    Step-by-step workaround instructions
    2 steps
    Show steps Hide steps
    Step-by-step procedure
    1. Enable trace flag 4696, or avoid querying sys.dm_exec_requests for databases that are recovering.
    2. Alternatively, uninstall the update.

Technical details

Data sheet · Security · Downloads · Components Click to collapse or expand

Data sheet

Released
2026-10-13
Classification
Security Updates
Type
Cumulative update
Servicing branch
CU
Restart
Required
Replaces
KB5122048, KB5122769, KB5104822, KB5096981
+10 earlier KB5101346, KB5093421, KB5084896, KB5089899, KB5081495, KB5083245, KB5077896, KB5077466, KB5075211, KB5078298
Replaced by
KB5129299
VersionBuildChannel
2025 17.0.5015.4 General availability

Security

24 vulnerabilities fixed
23 important 1 not rated
VulnerabilitySeverityCVSS
CVE-2026-32176
SQL Server Elevation of Privilege Vulnerability
 Important 6.7
CVE-2026-116933
Microsoft SQL Server Remote Code Execution Vulnerability
 Important —
CVE-2026-65674
Microsoft SQL Server Remote Code Execution Vulnerability
 Important —
CVE-2026-67625
Microsoft SQL Server Remote Code Execution Vulnerability
 Important —
CVE-2026-67626
Microsoft SQL Server Denial of Service Vulnerability
 Important —
CVE-2026-67628
Microsoft SQL Server Information Disclosure Vulnerability
 Important —
CVE-2026-68883
Microsoft SQL Server Elevation of Privilege Vulnerability
 Important —
CVE-2026-70189
Microsoft SQL Server Remote Code Execution Vulnerability
 Important —
CVE-2026-83945
Microsoft SQL Server Remote Code Execution Vulnerability
 Important —
CVE-2026-85876
Microsoft SQL Server Elevation of Privilege Vulnerability
 Important —
CVE-2026-85886
Microsoft SQL Server Remote Code Execution Vulnerability
 Important —
CVE-2026-85888
Microsoft SQL Server Information Disclosure Vulnerability
 Important —
CVE-2026-85919
Microsoft SQL Server Elevation of Privilege Vulnerability
 Important —
CVE-2026-88081
Microsoft SQL Server Information Disclosure Vulnerability
 Important —
CVE-2026-88082
Microsoft SQL Server Elevation of Privilege Vulnerability
 Important —
CVE-2026-88083
Microsoft SQL Server Remote Code Execution Vulnerability
 Important —
CVE-2026-88085
Microsoft SQL Server Elevation of Privilege Vulnerability
 Important —
CVE-2026-88086
Microsoft SQL Server Information Disclosure Vulnerability
 Important —
CVE-2026-88088
Microsoft SQL Server Elevation of Privilege Vulnerability
 Important —
CVE-2026-88089
Microsoft SQL Server Remote Code Execution Vulnerability
 Important —
CVE-2026-94512
SQL Server Remote Code Execution Vulnerability
 Important —
CVE-2026-94520
Microsoft SQL Server Denial of Service Vulnerability
 Important —
CVE-2026-96956
SQL Server Elevation of Privilege Vulnerability
 Important —
CVE-2026-94530
Not rated —

Downloads (Microsoft Update Catalog)

Package 2025
415.6 MB
sqlserver2025-kb5126967-x64.exe Main update · KB5126967 SHA-1: 0d1ecef9…fa9d2d

Updated components

145 files changed since the previous update for the same versions.

Top changed componentsFiles
SQL Server Engine115
SQL Server PolyBase3

Page history

  1. Superseded by KB5129299

    Added CVE-2026-116933 (Important)

Sources

Updated
Cited passages from Microsoft's official notes (27)
  1. 1. Addresses an input-validation issue in SQL Server Virtual Device Interface (VDI) and SQL Writer backup paths in which malformed size values potentially cause out-of-bounds memory access. support.microsoft.com
  2. 2. Addresses an integer handling issue in SQL Server backup and restore metadata processing that potentially allows a local authenticated user to gain elevated privileges and cause a service to stop responding. support.microsoft.com
  3. 3. Addresses an issue that causes the SQL Server process to terminate unexpectedly while working with external data sources. support.microsoft.com
  4. 4. Fixes a security vulnerability in the SQL Server Virtual Device Interface (VDI) in which an out-of-bounds write action potentially occurs while opening a virtual device set. support.microsoft.com
  5. 5. Fixes a security vulnerability in the SQL Server Virtual Device Interface (VDI) in which an out-of-bounds read or write action potentially occurs while processing transferred data during backup or restore operations. support.microsoft.com
  6. 6. Resolves a security vulnerability in PolyBase by improving validation during data processing. support.microsoft.com
  7. 7. Fixes unsafe deserialization of PolyBase rollback queue data so that malformed payloads are rejected. support.microsoft.com
  8. 8. Addresses an input-validation issue in SQL Server Virtual Device Interface (VDI) and SQL Writer backup paths in which malformed size values potentially cause out-of-bounds memory access. support.microsoft.com
  9. 9. Addresses an integer handling issue in SQL Server backup and restore metadata processing that potentially allows a local authenticated user to gain elevated privileges and cause a service to stop responding. support.microsoft.com
  10. 10. Fixes multiple memory-corruption and memory-disclosure vulnerabilities in SQL Server's SQL Satellite protocol message parsing logic that's used by Machine Learning Services and Language Extensions. support.microsoft.com
  11. 11. Fixes invalid memory-read vulnerability in SQL Server's AI_GENERATE_EMBEDDINGS runtime parameter processing. support.microsoft.com
  12. 12. Fixes an issue in which MSDASQL-linked server connections fail if the provider string does not include a user ID (UID). support.microsoft.com
  13. 13. Fixes a buffer overflow that occurs if merge replication processes more than 250 WebSync XML nickname entries. support.microsoft.com
  14. 14. Fixes an issue in replication operations that affects data validation. support.microsoft.com
  15. 15. Fixes an issue in merge replication Web Synchronization operations that affects data validation. support.microsoft.com
  16. 16. Fixes an issue in input data processing for change event streaming. support.microsoft.com
  17. 17. Limits LoginSid processing within the SQL Trace reader to the internal buffer size to prevent malformed trace data from causing an out-of-bounds read action. support.microsoft.com
  18. 18. Adds validation of FILESTREAM fragment size on Availability Group secondary replicas to reject oversized fragments. support.microsoft.com
  19. 19. Adds validation for delta table schema. support.microsoft.com
  20. 20. Updates shared memory handling. support.microsoft.com
  21. 21. Updates the third-party archive-extraction component that SQL Server uses if external language and external library packages are installed. support.microsoft.com
  22. 22. Improves security and reliability in replication security metadata handling during Subscriber database restore and upgrade. support.microsoft.com
  23. 23. Improves security and reliability for the Log Reader Agent in a heterogeneous transactional replication scenario. support.microsoft.com
  24. 24. Improves security and reliability for the change feed configuration. support.microsoft.com
  25. 25. Strengthens authorization checks for certain replication-related database operations to prevent unintended disclosure of database information. support.microsoft.com
  26. 26. Linked server queries that use the MSDASQL (OLE DB Provider for ODBC Drivers) provider and specify a provider string (@provstr) fail and return the following error message: support.microsoft.com
  27. 27. Queries against sys.dm_exec_requests might raise an access violation and generate a dump file if they run while a database is still recovering. support.microsoft.com
Checked automatically: 7 of 8 checks passed, 27 quoted passages · compared with Microsoft's page on Nov 14, 2026
  • Quotes found in the official pages: passed
  • Numbers found in the sources: passed
  • Vulnerabilities from the dossier only: passed
  • Links to allowed domains only: passed
  • Every official change covered: passed
  • Readable plain text: passed
  • Changes confirmed by the file list: passed
  • Sources agree: not passed

A second AI read the text against the sources: correctness 3/5, clarity 4/5, completeness 5/5. How we work

Published by The Update Bureau. Written with AI from Microsoft's own documents, checked by rules and a second AI. How we work · Report a mistake