KB5090408 — Security Update for SQL Server 2019 GDR

Overview

KB5090408 is a critical security update released on May 12, 2026, for Microsoft SQL Server 2019 running on x64-based Windows systems. This update addresses multiple high-severity vulnerabilities that could allow remote code execution, privilege escalation, information disclosure, and denial of service attacks against SQL Server instances.

The update is part of the General Distribution Release (GDR) servicing branch and provides essential security fixes without introducing new features or non-security related changes. Organizations running SQL Server 2019 in production environments should prioritize the deployment of this update to maintain database security and compliance.

Security Vulnerabilities Addressed

This security update resolves several critical vulnerabilities in Microsoft SQL Server 2019:

Remote Code Execution Vulnerability

A critical buffer overflow vulnerability in the SQL Server query processing engine could allow authenticated attackers to execute arbitrary code with elevated privileges. This vulnerability affects the core database engine and could be exploited through specially crafted SQL queries containing malformed parameters.

Privilege Escalation Vulnerability

An elevation of privilege vulnerability allows low-privileged database users to gain unauthorized administrative access through improper validation of stored procedure execution contexts. Attackers could exploit this vulnerability to access sensitive data or modify database configurations.

Information Disclosure Vulnerability

A vulnerability in the query optimization component could expose sensitive information through cached execution plans. This issue affects environments where multiple users share the same SQL Server instance and could lead to unauthorized access to confidential data.

Denial of Service Vulnerability

Malformed connection requests could cause SQL Server service interruption through resource exhaustion. This vulnerability could be exploited to disrupt database availability and impact business operations.

Affected Systems

This update applies to the following SQL Server 2019 configurations:

Installation Process

The installation process for KB5090408 varies depending on the deployment method chosen:

Standalone Installation

For standalone installations, download the update package from Microsoft Update Catalog and run the installer with administrative privileges. The installation process will automatically detect the SQL Server 2019 instance and apply the necessary updates.

SQLServer2019-KB5090408-x64.exe /quiet /IAcceptSQLServerLicenseTerms

Enterprise Deployment

Enterprise environments should use centralized deployment tools such as WSUS or SCCM to ensure consistent application across all SQL Server instances. Create deployment packages targeting systems with SQL Server 2019 GDR installations.

Verification Commands

After installation, verify the update was applied successfully using the following SQL query:

SELECT @@VERSION;
SELECT SERVERPROPERTY('ProductVersion') AS Version,
       SERVERPROPERTY('ProductLevel') AS Level,
       SERVERPROPERTY('Edition') AS Edition;

The version number should reflect the updated build number that includes the security fixes from KB5090408.

Security Recommendations

In addition to applying this security update, organizations should implement the following security best practices:

• Network Segmentation: Isolate SQL Server instances from untrusted networks and implement firewall rules to restrict database access
• Authentication: Use Windows Authentication where possible and implement strong password policies for SQL Server authentication
• Monitoring: Enable SQL Server audit logging and monitor for suspicious database activities
• Backup and Recovery: Maintain current database backups and test recovery procedures regularly
• Patch Management: Establish a regular patching schedule to ensure timely application of security updates

Impact Assessment

Organizations should assess the potential impact of this update on their SQL Server environments:

Performance Considerations

The enhanced security checks implemented in this update may cause minimal performance impact on query execution. Most environments will not notice significant changes, but systems with high query volumes should monitor performance metrics after installation.

Application Compatibility

Applications using standard SQL Server features should continue to function normally after applying this update. However, applications relying on deprecated features or undocumented behaviors may require testing to ensure continued compatibility.

Maintenance Windows

Plan for appropriate maintenance windows as the installation requires a SQL Server service restart. The restart duration depends on database size and recovery model configuration, typically ranging from 2-15 minutes for most environments.