SQL Server Patching Is Not Optional - Here Is Why It Matters

SQL Server cumulative updates are the primary mechanism Microsoft uses to deliver bug fixes, security patches, and stability improvements between major releases. Falling behind on them is one of the most common - and most avoidable - risks we see in Australian SQL Server environments. If your instances are running unpatched builds, you are carrying known vulnerabilities and documented bugs that Microsoft has already fixed.

That is the short answer. The longer answer involves understanding what you are actually leaving on the table when patching gets deprioritised.

What Are SQL Server Cumulative Updates and How Do They Work?

Microsoft releases SQL Server cumulative updates (CUs) on a regular cadence, typically every eight weeks for mainstream supported versions. Each CU is cumulative, meaning it contains all fixes from every previous CU in that release cycle. You do not need to apply them sequentially. If you are on SQL Server 2019 CU1 and the current release is CU27, applying CU27 brings you fully current in a single step.

This is different from how Windows patching works, and it trips up a lot of teams who assume they need to step through every update. You do not.

Each CU addresses a specific list of issues. Microsoft publishes detailed Knowledge Base articles for every release, documenting exactly which bugs are fixed, which are security-related, and whether any require trace flags or configuration changes post-install. The SQL Server 2019 release history alone covers hundreds of individual fixes across its CU releases.

Service Packs, which were a separate concept in older versions like SQL Server 2012 and 2014, are no longer part of the patching model from SQL Server 2017 onwards. CUs are now the primary delivery mechanism for all fixes.

What Happens When You Skip SQL Server Cumulative Updates?

The consequences of falling behind on SQL Server patching fall into three categories: security exposure, operational instability, and supportability risk.

Security exposure is the most immediate concern. Microsoft regularly includes fixes for CVEs (Common Vulnerabilities and Exposures) in CU releases. Some of these are rated Critical under the CVSS scoring system, meaning remote code execution or privilege escalation is possible without authentication. Running an unpatched instance in a network-connected environment with known CVEs is a genuine risk, not a theoretical one.

Operational instability is less obvious but just as damaging. Query processor bugs, memory manager issues, and corruption-related defects have all been resolved through CU releases. We have seen environments where mysterious query timeouts, unexpected failovers, or backup failures were traced back to known bugs fixed in a CU the team had never applied. The fix existed. They just had not deployed it.

Supportability risk matters when things go wrong. If you log a support case with Microsoft and your instance is significantly behind on cumulative updates, the first thing they will ask is whether the issue is reproducible on a current build. In practice, this means your incident response time blows out while you patch under pressure. That is the worst possible time to be applying updates.

How Do You Check Which CU Your SQL Server Is Running?

Checking your current build is straightforward. Run this query against any instance:

SELECT
    @@SERVERNAME AS ServerName,
    @@VERSION AS FullVersion,
    SERVERPROPERTY('ProductVersion') AS ProductVersion,
    SERVERPROPERTY('ProductLevel') AS ProductLevel,
    SERVERPROPERTY('ProductUpdateLevel') AS CULevel,
    SERVERPROPERTY('Edition') AS Edition;

The ProductVersion output gives you a four-part build number such as 15.0.4375.4. You can cross-reference this against the official Microsoft SQL Server builds list to determine exactly which CU you are on and how far behind you are.

For environments with multiple instances, running this across all servers manually is not practical. A centralised inventory using a management tool or a linked server query across your estate gives you a clear picture of where every instance sits. In our experience running SQL Server health checks across Australian organisations, it is common to find instances running builds that are 18 to 24 months out of date - sometimes longer.

What Is a Practical CU Strategy for Production Environments?

A workable SQL Server CU strategy does not mean applying every update the day it drops. It means having a defined process that keeps you reasonably current without introducing unnecessary change risk.

Here is a practical approach that works for most production environments:

  1. Monitor releases. Subscribe to the Microsoft SQL Server Blog and set up alerts for new CU releases. You should know when a new CU is available within a day or two of release.

  2. Wait 2-4 weeks before applying to production. This gives the community time to surface any regression issues. Microsoft occasionally releases CUs that introduce new problems, and a short waiting period catches most of these before they affect you.

  3. Apply to non-production first. Deploy the CU to development and test environments. Run your standard regression tests. Verify that nothing breaks before touching production.

  4. Schedule a maintenance window. CU installs on SQL Server typically require a service restart. Plan this during a low-traffic period and communicate the window to application owners in advance.

  5. Validate post-install. After applying the CU, confirm the build number matches expectations, check the SQL Server error log for any startup warnings, and verify that key application functions are working normally.

  6. Document everything. Record the date, the CU applied, who performed the work, and any issues encountered. This matters for audit purposes and for future troubleshooting.

Aim to stay within one to two CUs of the current release. This is a realistic target that balances stability with security without requiring constant change activity.

Are There Any Risks to Applying SQL Server Cumulative Updates?

Honest answer: yes, there are risks, and pretending otherwise does not help anyone make informed decisions.

The most common risk is a regression introduced by the CU itself. This is relatively rare but it does happen. The mitigation is the waiting period and non-production testing described above.

There is also the risk of the restart itself. In environments without High Availability configurations like Always On Availability Groups or Failover Cluster Instances, a CU install means a service restart and a period of downtime. This needs to be planned and communicated.

For environments with Always On Availability Groups, you can apply CUs in a rolling fashion, patching secondary replicas first and then failing over to minimise downtime. This is the recommended approach for high-availability environments and Microsoft documents the rolling upgrade process in detail.

The risk of not patching, however, consistently outweighs the risk of patching. A known CVE with a public exploit is a concrete threat. A potential regression from a CU is a manageable one.

Key Takeaways

  • SQL Server cumulative updates are released approximately every eight weeks and contain all previous fixes - you do not need to apply them sequentially.
  • Unpatched instances carry known security vulnerabilities (CVEs) and documented bugs that Microsoft has already resolved.
  • From SQL Server 2017 onwards, CUs replace Service Packs as the primary patching mechanism.
  • A practical CU strategy involves monitoring releases, waiting 2-4 weeks, testing in non-production, and maintaining a documented maintenance window process.
  • Always On Availability Groups support rolling CU upgrades, which minimises production downtime during patching.

What Should You Do Next?

If you are not certain which build every SQL Server instance in your environment is running, that is the first problem to solve. The query above gives you the answer for any single instance. Getting a complete picture across your estate is a different challenge, and it is one of the things a structured SQL Server health check addresses directly.

At DBA Services, our health checks routinely identify instances running outdated builds, missing critical updates, and carrying unaddressed CVEs. We have seen this across organisations of every size - from small businesses running a single instance to large enterprises with dozens of servers. Falling behind on SQL Server patching is not a sign of negligence. It is usually a sign that the team is busy and patching has not been given the priority and process it needs.

If you want a clear view of where your environment stands, contact DBA Services to arrange a SQL Server health check. We will tell you exactly what you are running, what you should be running, and what the practical path forward looks like.