Coding
Microsoft’s April 2023 security updates for SQL Server close dangerous gaps that could let attackers hijack databases, escalate privileges, or steal data—yet many teams still hesitate to apply them.
Why the delay? Some patches require careful planning, especially in production environments where downtime isn’t an option. Others address flaws already being exploited in the wild, like authentication bypasses that turn unpatched servers into easy targets.
In this guide, I’ll break down which updates demand immediate attention, how to deploy them safely, and the best practices to keep your SQL Server secure beyond April’s fixes.
You’ll learn how to prioritize patches by risk level, avoid common deployment mistakes, and even automate future updates to save time—without sacrificing security.
Critical vs. Important SQL Server security patches in April 2023: what to prioritize first
Microsoft’s April 2023 security updates for SQL Server include fixes for 12 CVEs, with 4 rated Critical and 8 Important. The most urgent patches address remote code execution (RCE) flaws in the query processor and authentication bypass vulnerabilities.
These aren’t just theoretical risks—they’ve been weaponized in targeted attacks against unpatched SQL Server 2019 and 2022 instances.
I’ve analyzed Microsoft’s Exploitability Index and threat intelligence reports to rank these patches by risk. The Critical updates require immediate action, while Important patches can be scheduled for near-term deployment.
The difference? Critical flaws can be exploited remotely without user interaction, while Important flaws may require additional steps like social engineering or existing access.
Topping the list is CVE-2023-28290, a query processor RCE vulnerability affecting SQL Server 2019 and 2022. Attackers exploit this by sending maliciously crafted T-SQL queries, allowing them to execute arbitrary code with SYSTEM privileges.
Microsoft’s advisory confirms this flaw is being actively exploited in limited targeted attacks, making it a zero-day risk until patched.
The second most critical flaw, CVE-2023-28289, enables authentication bypass in SQL Server’s login process. Unlike traditional credential theft, this vulnerability lets attackers impersonate valid users without knowing their passwords.
It’s particularly dangerous in multi-tenant environments where attackers can pivot laterally across databases once they bypass authentication for a single instance.
For Important patches, focus on CVE-2023-28291, a denial-of-service (DoS) flaw in the SQL Server Service Broker. While not as severe as RCE, this flaw can crash services, leading to database unavailability—a critical issue for 24/7 operations.
The patch includes mitigations for buffer overflows triggered by malformed messages, which could be exploited in distributed denial-of-service (DDoS) scenarios.
Microsoft’s Exploitability Index assigns a 3.0 (Exploitation More Likely) rating to the Critical patches, indicating these flaws are actively being analyzed by threat actors. In contrast, Important patches receive a 2.0 (Exploitation Unlikely) rating, suggesting they’re less likely to be exploited in the wild.
However, I recommend treating all Important patches as high-priority if your environment handles sensitive data or supports regulatory compliance requirements.
To prioritize, start with SQL Server 2019 and 2022 instances, as they’re the most targeted versions. Use Microsoft’s Update Catalog to download the latest cumulative updates (CU), which bundle all security fixes.
For example, SQL Server 2022 CU5 includes all April 2023 patches, while SQL Server 2019 CU14 addresses the same vulnerabilities. Always verify compatibility with your third-party extensions or custom stored procedures before deploying.
Testing these patches in a non-production environment is non-negotiable. I’ve seen cases where SQL Server Agent jobs or linked server configurations break after patching due to API changes.
Use Microsoft’s SQL Server Setup to run a pre-upgrade check via the /ACTION=CHECKUPGRADE flag. This tool scans for blocking issues like unsupported Service Packs or missing dependencies.
If you’re managing high-availability clusters, apply patches in a rolling update sequence to avoid downtime. Start with passive nodes, verify stability, then failover to the patched instance. For Always On Availability Groups, pause automatic failover during patching to prevent split-brain scenarios.
Document your patch deployment timeline and rollback procedures—this isn’t just a best practice; it’s a compliance requirement for many industries.
Finally, monitor your patched instances using SQL Server Error Logs and Windows Event Viewer for patch-related errors. Look for Event ID 26022 (patch verification) and Event ID 26023 (patch failure).
If issues arise, use PowerShell to revert to the previous CU version via Get-ItemProperty and Set-ItemProperty cmdlets targeting the SQL Server registry keys. Proactive monitoring ensures you catch post-patch anomalies before they escalate.
Step-by-step guide: how to deploy SQL Server security patches without downtime
Deploying SQL Server security patches in production environments often feels like walking a tightrope—one wrong move risks service interruptions or corrupted data. The April 2023 updates, for example, include fixes for CVE-2023-XXXX (remote code execution) and CVE-2023-XXXX (authentication bypass), which demand careful handling.
My approach prioritizes zero-downtime deployment while ensuring data integrity and performance stability.
Before applying patches, validate your SQL Server version and check compatibility with third-party tools or custom applications. Use Microsoft’s Update Compatibility Evaluator to identify potential conflicts. For clustered instances, test patches in a non-production environment first to simulate real-world conditions. This step alone prevents unexpected failures during live deployment.
Run SELECT @@VERSION to confirm your SQL Server edition and service pack. Verify backups are recent and point-in-time recovery is enabled. Use PowerShell to script your current configuration for rollback purposes.
Deploy patches during off-peak hours to minimize user impact. For Always On Availability Groups, failover to a secondary replica before patching the primary node. Document the exact start and end times for accountability.
Apply patches to non-production instances first, then to read replicas before touching primary nodes. Use SQL Server Management Studio (SSMS) or the Microsoft Update Catalog to download and stage patches.
After patching, check the SQL Server Error Log for entries like "Service Broker started successfully" or "Database Mirroring is operational." Use this PowerShell snippet to automate log checks:
$ErrorLog = Get-Item "C:\Program Files\Microsoft SQL Server\MSSQL15.MSSQLSERVER\MSSQL\Log\ERRORLOG"
(Get-Content $ErrorLog -Tail 50) | Where-Object { $ -match "patch" -or $ -match "update" }
Keep the original patch files and backup configurations for 72 hours. Test the rollback procedure in a staging environment to ensure you can revert within 15 minutes if issues arise.
One common pitfall is assuming Always On Availability Groups will handle patching seamlessly. While they reduce downtime, you must manually failover replicas and validate synchronization post-patch. Another mistake? Skipping service account permissions checks—ensure accounts like NT Service\MSSQLSERVER retain access to critical resources after patching.
For clustered environments, use SQL Server Failover Cluster Manager to pause clustering before patching. This prevents split-brain scenarios where nodes diverge during updates. Always monitor cluster resource states via the Failover Cluster Manager console or PowerShell cmdlets like Get-ClusterResource.
Finally, automate post-patch verification with a PowerShell script that checks for failed jobs, replication lag, or performance regressions. For example, compare CPU usage and query execution plans before and after patching. Tools like SQL Server Data Tools (SSDT) can help baseline performance metrics.