KB5122048: Cumulative update for SQL Server 2025, CU branch, September 2026. Parallel session results can be wrong; recovery queries can crash

• Creating a database user with certain Unicode characters in the display name no longer fails with character-mapping or token errors.¹
  Addresses unsupported Kanji or other Unicode characters in the system default code page.
• Fixes a security vulnerability in sign-in requests that use Microsoft Entra authentication.⁶
• Creating a database user from Microsoft Entra ID no longer fails with certain Unicode display names.⁷
  Fixes failure with WITH OBJECT_ID when the display name contains Kanji or other Unicode characters unsupported by the system default code page.
• A class ID lookup in enclave code no longer reads arbitrary memory.¹³
• An error from sys.fn_external_policy_actions_assigned_to_principal is formatted correctly.²¹
• Audit records consistently include sensitivity information when applicable.²²
  Fixes inconsistent population of data_sensitivity_information for the SCHEMA_OBJECT_ACCESS_GROUP audit action group.

For: All platforms

• An authenticated remote procedure call that overflows a buffer no longer causes the SQL Server process to end unexpectedly.²
  Fixes a buffer overflow during an authenticated Tabular Data Stream (TDS) remote procedure call (RPC).

For: All platforms

• Addresses a vulnerability in the SQL Server managed-backup stored procedures for Microsoft Azure.³
  Affects managed_backup.sp_get_encryption_option and managed_backup.sp_do_backup; customers using managed backup should apply the update through standard SQL Server servicing.
• Addresses a security and reliability issue affecting SQL Server Agent in certain operating conditions.⁸

For: Windows SQL Server instances

• The SQL Server WMI provider handles malformed input correctly while keeping its existing behavior for valid input.⁴

For: All platforms

• An assertion failure no longer occurs in this optimized-locking scenario.⁵
  The failure occurred when a row was requalified after being forwarded.

For: All platforms

• A secondary replica can join an availability group with a 64-character name and cluster type NONE or EXTERNAL.⁹

For: All platforms

• The SUBSTRING function no longer reads beyond its allocated buffer when processing malformed DBCS varchar data in a natively compiled stored procedure.¹⁰
• Converting or truncating certain nvarchar values no longer causes an access violation that ends the SQL Server process.¹¹
  Fixes the issue for values containing an ideographic variation sequence under a variation selector sensitive (_VSS) collation in a natively compiled stored procedure.
• Streaming certain nvarchar(max) data no longer overwrites heap memory or causes the server to stop responding.¹²
  Occurs with a variation selector sensitive (_VSS) collation in a natively compiled stored procedure when TEXTSIZE truncates data and small TDS packet sizes are used.

For: All platforms

• Starting PolyBase services with modified command-line parameters no longer opens a raw TCP listener for the DW Engine and DMS channels.¹⁴
  Applies to the DMS control and data channels.

For: All platforms

• Fixes how SQL Server handles DTD attribute lists for the xml data type.¹⁵
• A query with an extremely large USE PLAN XML declaration no longer causes an access violation that can end the SQL Server process.¹⁶
• Processing a specially crafted XML format file no longer causes an integer overflow that can make SQL Server stop responding or end unexpectedly.²⁰
  Applies to files processed through OPENROWSET(BULK ...) or BULK INSERT.

• The LEFT_SHIFT and RIGHT_SHIFT functions no longer cause arithmetic overflow or out-of-bounds memory access with specially crafted inputs.¹⁷
  The issue could cause the SQL Server process to end unexpectedly.
• Fixes field-offset validation for sql_variant values in the SqlDataRecord.SetBytes API, addressing a possible out-of-bounds heap write when CLR integration is enabled.²⁸

For: All platforms

• Addresses a security issue that could cause memory corruption when Extended Events input is not sufficiently validated.¹⁸
• Fixes vulnerabilities that could disclose information or cause a denial of service when the Database Engine reads a specially crafted Extended Events file.¹⁹
  The affected files have the *.xel extension.

For: Windows SQL Server instances

• The Buffer cache hit ratio performance counter no longer always shows zero in Performance Monitor.²³

For: All platforms

• Stronger input validation addresses a way for an authenticated user to disclose a limited amount of memory.²⁴
• Stronger input validation addresses a way for an authenticated user to disclose in-memory information.²⁵
• Stronger input validation addresses an issue where an authenticated user could supply a pointer that SQL Server reads, potentially causing a dump file or out-of-memory condition.²⁶
  SQL Server dereferences and reads the pointer but does not execute it.

For: All platforms

• Reported tempdb space usage is consistent after drop or truncate operations.²⁷
  Fixes the value reported by sys.dm_db_session_space_usage.

For: All platforms

• Change Event Streaming can deserialize events whose payloads contain certain characters.²⁹
• Serialization of large object data streamed through Change Event Streaming no longer causes SQL Server dump files.³⁰

For: Windows SQL Server instances

• Malformed or undersized backup metadata is rejected more safely.³¹
  Improves validation of metadata processed by the SQL Server VSS Writer.

For: Windows SQL Server instances

• SQL Server Agent checks task-agent components more thoroughly as it loads them.³²
  Improves security validation when SQL Server Agent loads task agent components.

For: All platforms

• SQL Server Agent handles certain input more reliably and securely.³³
  Improves the reliability and security of SQL Server Agent when it processes certain input.

For: Windows SQL Server instances

• Embedded attestation fields receive bounds checks when parsed.³⁴
  Adds bounds validation in sys.sp_describe_parameter_encryption.
• Buffer lengths in enclave code are validated more thoroughly.³⁷

For: All platforms

• Responses from S3-compatible external storage endpoints are validated more thoroughly during external data access.³⁵

For: All platforms

• SQL Server better protects information when processing and outputting certain internal event data.³⁶

For: Windows SQL Server instances

• Showplan input is handled more securely and reliably.³⁸

• Internal replication data is better protected during processing.³⁹
• Merge replication handles text data more securely and reliably.⁴⁰
• Replication operations receive improved validation and handling for security and reliability.⁴¹
• Queued updating subscriptions in transactional replication are more secure and reliable.⁴²
• Queued updating subscriptions in transactional replication are more secure and reliable.⁴³

For: Standard and Standard Developer editions on Windows

• Manual soft-NUMA configuration is available for the Standard and Standard Developer editions.⁴⁴

For: All platforms

• Managed Instance link supports linking multiple databases so they can be replicated and failed over together.⁴⁵
  Multiple-database link mode extends an existing SQL Server Always On availability group to Azure SQL Managed Instance.