Microsoft has published SQL Server 2025 Cumulative Update 4 (CU4), tracked as KB5081495 and build 17.0.4035.5. According to the release notes, this update contains 11 fixes delivered after SQL Server 2025 CU3 and updates both the SQL Server engine and Analysis Services builds.

The release touches several practical areas that DBAs and developers will recognize quickly: Database Mail in contained availability groups, msdb permissions during upgrade, Linux threading behavior, SSIS tooling, Full-Text Search, contained availability group auditing, JSON behavior, replication stability, and a Windows Server 2025-specific access violation scenario.

Known issues

Microsoft lists two known issues with CU4:

  • SESSION_CONTEXT in parallel plans: queries that use SESSION_CONTEXT may return incorrect results or produce access violation dump files when run in parallel query plans, especially if the session is reset for reuse.
  • Linked server queries using MSDASQL: linked server queries that use the MSDASQL provider and specify a provider string can fail with Msg 7416 indicating that no login-mapping exists.

Microsoft also points to the related known-issues documentation for each item. Removal of an issue from the source later would not, by itself, prove that it has been resolved.

Improvements and fixes

CU4 includes 11 verified fixes across a few main areas:

  • Database Mail and client tools: fixes a contained availability groups issue where DatabaseMail could send messages without attachments when using sp_RunMailQuery.
  • Upgrade and management services: addresses a problem where permissions on stored procedures and other msdb objects could be lost during SQL Server upgrade.
  • SQL Server on Linux: fixes a SQLPAL threading issue that could leave the server in an unintended wait state on an internal thread that does not support suspension.
  • Integration Services: corrects a case where DTSWizard.exe would not open if SQL Server was installed without SSIS features.
  • Search / Full-Text Search: fixes two search-related issues, including fdhost.exe stopping when indexing certain Word 6.0 documents and failures for inflectional Full-Text Search queries in version 2 languages that do not implement an IStemmer.
  • High availability and disaster recovery: resolves a memory corruption issue in contained availability group auditing and tightens database-adding behavior for contained availability groups and DBCreator.
  • SQL OS on Windows: fixes an access violation when querying sys.dm_xe_session_targets on Windows Server 2025 instances.
  • JSON: limits Json_contains comparison mode to 0 for exact match or 1 for pattern match, with 0 as the default.
  • Replication: addresses non-yielding scheduler errors and dump files that could appear during heavy lazy writer I/O.

For teams evaluating the release, the scope is broad rather than narrowly focused on a single subsystem: CU4 combines engine fixes, platform-specific corrections, and behavior changes in areas such as Json_contains and contained availability groups.

Official source