SQL Server 2025 CU3 – Critical Fixes You Should NOT Ignore (Regex & Vector Bugs Fixed) ⚠️

SQL Server 2025 CU3 – Critical Fixes You Should NOT Ignore (Regex & Vector Bugs Fixed)

Hi SQL SERVER Guys,

If you are working with SQL Server, you already knows that performing the cumulative updates is very important since it is the way chosen by Microsoft both to fix bugs and to apply security patches. You really should not skip them!

With Cumulative Update 3 (CU3), released in March, 12 2026 Microsoft fixed several important issues — including two critical ones we already talked about in my recent posts:

Why CU3 Matters

CU3 is not just a minor patch.

It contains engine-level fixes that impact:

  • Performance scalability
  • Regex engine stability
  • Vector processing
  • High Availability scenarios
  • Linux deployments

👉 Full official Microsoft reference: 

SQL Server 2025 CU3 – Improvements and Fixes

Improvement and Fixes included in this update 

This is a readable breakdown of all fixes included in CU3:

Bug ID What Was Fixed Area Component Platform
4836787 Reduces CPU contention on high-core servers by fixing cache line conflicts (false sharing), improving overall scalability. Engine Columnstore All
4836829 General scalability improvements for multi-core systems under heavy workloads. Engine Columnstore All
4836855 Improves backup performance by aligning I/O structures with CPU cache (64-byte alignment). Engine Backup/Restore All
4845346 🚨 Fixes a crash when using VECTOR functions in SqlLocalDB. Critical for AI/vector workloads. Engine SqlLocalDB Windows
4852207 Fixes crashes caused by the interaction between optimized locking and change tracking. Engine Storage Engine All
4953808 Fixes startup failures in Contained Availability Groups (configure-only replicas). Engine High Availability All
4954946 🚨 Fixes SqlLocalDB crash when using REGEX functions. Critical for new regex engine stability. Engine SqlLocalDB Windows
4955141 Fixes issues with Log Shipping and Availability Groups after failover. Engine High Availability All
4955489 Fixes typo in Linux DMV (ios_in_progress) to ensure correct monitoring. Connectivity Linux Linux
4986175 Introduces secure bulk operations via Bulkadmin without requiring sysadmin (preview). Engine Security Linux
5002842 Fixes a low-level crash in SQLPAL when requesting specific CPU register contexts. SQLPAL Core Engine Linux
5004820 Adds configurable timeout for full-text indexing batches to prevent long-running operations. Engine Search All
5004893 Fixes incorrect database file paths after edition changes on Linux. Engine Linux Linux
5004967 Adds support for symbolic links in file attribute handling APIs. Engine Linux Linux
5013499 Adds configuration option to allow Bulkadmin operations via allowlist. Engine Security Linux


Final Thought

SQL Server 2025 is introducing powerful features

  • Regex engine
  • Vector data type (AI-ready)
  • Advanced execution pipelines

But with innovation comes instability in early builds.

👉 then CU3 is a must-have update if you are working with these features.

Sometimes performance is not just about tuning queries...

...it starts with running the right build.


👉 If you missed my previous about the VECTOR Data Type post just click here: SQL Server 2025 Vector Data Type – Why It Matters for AI (and Known Bugs) ⚠️


Luca Biondi @2026

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