KB5084820 is a security update released on April 14, 2026, for SQL Server 2016 SP3 Azure Connect Feature Pack. This update addresses multiple critical security vulnerabilities that could allow remote code execution and privilege escalation in Azure-connected SQL Server environments.
Knowledge BaseKB5084820SQL Server
KB5084820 — Security Update for SQL Server 2016 SP3 Azure Connect Feature Pack
KB5084820 is a security update released April 14, 2026, that addresses critical vulnerabilities in SQL Server 2016 SP3 Azure Connect Feature Pack, including remote code execution and privilege escalation issues.
16 April 2026 12 min read —
KB5084820SQL ServerSecurity Update 4 fixes 12 min Microsoft SQL Server 2016 for x64-based Systems Service Pack 3 Azure Connect Feature PackDownload
Quick Overview
PowerShell—Check if KB5084820 is installed
PS C:\> Get-HotFix -Id KB5084820# Returns patch details if KB5084820 is installed
Download Update
Download from Microsoft Update Catalog
Get the official update package directly from Microsoft
Diagnostic
Issue Description
Issue Description
This security update addresses several critical vulnerabilities in SQL Server 2016 SP3 Azure Connect Feature Pack that could be exploited by attackers to gain unauthorized access or execute malicious code:
- Remote Code Execution Vulnerability (
CVE-2026-0847): An authenticated attacker could execute arbitrary code on the SQL Server instance through malformed Azure Connect requests - Privilege Escalation Vulnerability (
CVE-2026-0848): A low-privileged user could escalate privileges to sysadmin level through Azure Connect authentication bypass - Information Disclosure Vulnerability (
CVE-2026-0849): Sensitive Azure connection strings and credentials could be exposed through improper error handling - Denial of Service Vulnerability (
CVE-2026-0850): Malformed Azure Connect packets could cause the SQL Server service to crash or become unresponsive
These vulnerabilities affect SQL Server instances with Azure Connect Feature Pack enabled and configured for hybrid cloud scenarios.
Analysis
Root Causes
Root Cause
The vulnerabilities stem from insufficient input validation and improper authentication handling in the Azure Connect Feature Pack components. Specifically, the issues are caused by inadequate sanitization of Azure authentication tokens, improper bounds checking in network packet processing, and insufficient privilege validation during Azure hybrid operations.
Overview
KB5084820 is a critical security update released on April 14, 2026, for Microsoft SQL Server 2016 Service Pack 3 Azure Connect Feature Pack. This update addresses four significant security vulnerabilities that could allow attackers to execute remote code, escalate privileges, disclose sensitive information, or cause denial of service in SQL Server environments with Azure connectivity enabled.
Security Vulnerabilities Addressed
This update resolves the following Common Vulnerabilities and Exposures (CVE):
| CVE ID | Vulnerability Type | CVSS Score | Impact |
|---|---|---|---|
CVE-2026-0847 | Remote Code Execution | 8.8 (High) | Arbitrary code execution through Azure Connect |
CVE-2026-0848 | Privilege Escalation | 7.8 (High) | Unauthorized privilege escalation to sysadmin |
CVE-2026-0849 | Information Disclosure | 6.5 (Medium) | Exposure of Azure credentials and connection strings |
CVE-2026-0850 | Denial of Service | 5.3 (Medium) | Service crashes through malformed packets |
Affected Systems
This security update applies specifically to:
- Microsoft SQL Server 2016 for x64-based Systems Service Pack 3 with Azure Connect Feature Pack installed
- Supported Operating Systems: Windows Server 2012 R2, Windows Server 2016, Windows Server 2019, Windows Server 2022
- Architecture: x64 only (32-bit systems are not supported)
- Editions: Enterprise, Standard, Web, Express (with Azure Connect Feature Pack)
Note: Systems without Azure Connect Feature Pack installed are not affected by these vulnerabilities and do not require this update.
Technical Details
Remote Code Execution (CVE-2026-0847)
The most critical vulnerability allows authenticated attackers to execute arbitrary code on the SQL Server system through specially crafted Azure Connect authentication requests. The vulnerability exists in the authentication token processing module where insufficient input validation could lead to buffer overflow conditions.
Privilege Escalation (CVE-2026-0848)
This vulnerability enables low-privileged database users to escalate their privileges to sysadmin level by exploiting weaknesses in the Azure Connect authorization validation. The issue occurs when Azure-authenticated users can bypass local SQL Server security policies during hybrid operations.
Information Disclosure (CVE-2026-0849)
Sensitive Azure connection information, including connection strings and authentication tokens, could be exposed through verbose error messages and debug logs. This vulnerability could allow attackers to obtain credentials for further attacks on Azure resources.
Denial of Service (CVE-2026-0850)
Malformed network packets sent to the Azure Connect service could cause the SQL Server service to crash or become unresponsive. This vulnerability could be exploited to disrupt database operations and availability.
Installation Requirements
System Requirements
- SQL Server 2016 Service Pack 3 (Build 13.0.6300.2 or later)
- Azure Connect Feature Pack version 1.0 or later
- Administrative privileges on the target system
- Minimum 100 MB free disk space
- Active internet connection for Azure connectivity validation
Pre-Installation Checklist
- Verify SQL Server 2016 SP3 installation:
SELECT @@VERSION - Confirm Azure Connect Feature Pack is installed:
SELECT * FROM sys.dm_server_services WHERE servicename LIKE '%Azure Connect%' - Check available disk space:
Get-WmiObject -Class Win32_LogicalDisk | Select-Object DeviceID, FreeSpace - Schedule maintenance window for service restart
- Backup system and databases before installation
Post-Installation Verification
After installing KB5084820, verify the update was applied successfully:
Check Update Installation
Get-HotFix -Id KB5084820Verify SQL Server Version
SELECT SERVERPROPERTY('ProductVersion') AS Version, SERVERPROPERTY('ProductUpdateLevel') AS UpdateLevelTest Azure Connect Functionality
- Restart SQL Server services
- Verify Azure Connect service starts successfully
- Test Azure authentication and connectivity
- Monitor SQL Server error logs for any issues
- Validate hybrid query operations if applicable
Security Recommendations
In addition to applying this security update, Microsoft recommends the following security best practices:
- Network Segmentation: Isolate SQL Server systems with Azure Connect from untrusted networks
- Access Control: Implement least-privilege access principles for Azure Connect users
- Monitoring: Enable SQL Server audit logging and monitor for suspicious Azure Connect activities
- Regular Updates: Establish a regular patching schedule for SQL Server security updates
- Backup Strategy: Maintain current backups of databases and system configurations
Important: Organizations using SQL Server 2016 SP3 with Azure Connect Feature Pack in production environments should prioritize the installation of this security update due to the critical nature of the vulnerabilities addressed.
Resolution Methods
Key Fixes & Changes
01
Fixes remote code execution vulnerability in Azure Connect authentication (CVE-2026-0847)
This update patches the Azure Connect authentication module to properly validate and sanitize incoming authentication requests. The fix implements enhanced input validation for Azure Active Directory tokens and prevents buffer overflow conditions that could lead to arbitrary code execution. The updated authentication handler now includes bounds checking and proper memory management to prevent exploitation through malformed authentication packets.
02
Resolves privilege escalation through Azure Connect bypass (CVE-2026-0848)
The update strengthens privilege validation mechanisms in the Azure Connect Feature Pack by implementing additional authorization checks during hybrid operations. The fix ensures that Azure-authenticated users cannot bypass local SQL Server security policies and that privilege escalation attempts are properly blocked. Enhanced logging has been added to track privilege escalation attempts for security monitoring.
03
Prevents information disclosure of Azure credentials (CVE-2026-0849)
This security fix improves error handling and logging mechanisms to prevent sensitive Azure connection information from being exposed in error messages or log files. The update implements proper credential masking in error outputs and ensures that Azure connection strings, authentication tokens, and other sensitive data are not inadvertently disclosed through verbose error reporting or debugging information.
04
Addresses denial of service vulnerability in packet processing (CVE-2026-0850)
The update enhances the network packet processing routines in the Azure Connect Feature Pack to handle malformed or oversized packets gracefully. The fix implements proper packet validation, size limits, and error recovery mechanisms to prevent service crashes or hangs when processing invalid Azure Connect network traffic. Additional monitoring capabilities have been added to detect and log potential DoS attempts.
Validation
Installation
Installation
KB5084820 is available through multiple distribution channels:
Microsoft Update Catalog
Download the standalone package directly from Microsoft Update Catalog for manual installation. The update package is approximately 45 MB and requires administrative privileges for installation.
Windows Server Update Services (WSUS)
Enterprise environments can deploy this update through WSUS infrastructure. The update will appear in the SQL Server Products classification and can be approved for targeted deployment to SQL Server 2016 SP3 systems.
System Center Configuration Manager (SCCM)
Deploy through SCCM software update management for centralized enterprise deployment. Create deployment packages targeting systems with SQL Server 2016 SP3 Azure Connect Feature Pack installed.
Prerequisites
- SQL Server 2016 Service Pack 3 must be installed
- Azure Connect Feature Pack must be installed and configured
- Administrative privileges required for installation
- Minimum 100 MB free disk space on system drive
- SQL Server service restart required after installation
Installation Process
The update can be installed while SQL Server is running, but requires a service restart to complete the installation. Plan for maintenance windows accordingly. Installation typically takes 5-10 minutes depending on system performance.
If it still fails
Known Issues
Known Issues
The following issues have been identified after installing KB5084820:
Azure Connect Service Startup Delay
Some systems may experience a 30-60 second delay in Azure Connect service startup after applying the update. This is due to enhanced security validation during service initialization and does not indicate a problem. The delay will normalize after the first successful startup.
Temporary Azure Authentication Errors
Immediately after installation and service restart, Azure authentication may fail for 2-3 minutes while security tokens are refreshed. Applications should implement retry logic to handle temporary authentication failures during this period.
Increased Memory Usage
The enhanced security validation may result in a 5-10% increase in memory usage for the SQL Server process when Azure Connect features are actively used. Monitor memory utilization on systems with limited available RAM.
Compatibility with Third-Party Monitoring Tools
Some third-party SQL Server monitoring tools may report false security alerts due to the enhanced logging introduced in this update. Contact your monitoring tool vendor for updated signatures that recognize the new security logging patterns.
Important: Test this update in a non-production environment before deploying to production systems. Ensure that all Azure Connect functionality works as expected after the update.
Frequently Asked Questions
What does KB5084820 resolve?+
KB5084820 resolves four critical security vulnerabilities in SQL Server 2016 SP3 Azure Connect Feature Pack, including remote code execution (CVE-2026-0847), privilege escalation (CVE-2026-0848), information disclosure (CVE-2026-0849), and denial of service (CVE-2026-0850) vulnerabilities that could be exploited in Azure-connected SQL Server environments.
Which systems require KB5084820?+
This update is required for systems running Microsoft SQL Server 2016 Service Pack 3 for x64-based systems with Azure Connect Feature Pack installed. Systems without the Azure Connect Feature Pack are not affected and do not need this update. Supported operating systems include Windows Server 2012 R2 through Windows Server 2022.
Is KB5084820 a security update?+
Yes, KB5084820 is a critical security update that addresses four CVE-identified vulnerabilities with CVSS scores ranging from 5.3 to 8.8. The update includes fixes for remote code execution, privilege escalation, information disclosure, and denial of service vulnerabilities in the Azure Connect Feature Pack components.
What are the prerequisites for KB5084820?+
Prerequisites include SQL Server 2016 Service Pack 3 (Build 13.0.6300.2 or later), Azure Connect Feature Pack version 1.0 or later, administrative privileges, minimum 100 MB free disk space, and an active internet connection. A SQL Server service restart is required to complete the installation.
Are there known issues with KB5084820?+
Known issues include a 30-60 second delay in Azure Connect service startup, temporary Azure authentication errors for 2-3 minutes after installation, a 5-10% increase in memory usage during Azure operations, and potential false security alerts from third-party monitoring tools due to enhanced logging.
References (3)
1
KB5084820 : Mise à jour de sécurité pour SQL Server 2016 SP3 Azure Connect Feature PackArticle de support officiel de Microsoft pour la mise à jour de sécurité KB5084820https://support.microsoft.com/en-us/topic/kb5084820-description-of-the-security-update-for-sql-server-2016-sp3-azure-connect-feature-pack-april-14-2026-bc8bf4cb-40c2-470b-9316-33faefe75916
2Informations sur la version du Service Pack 3 de SQL Server 2016Informations sur les exigences et la compatibilité de SQL Server 2016 SP3https://support.microsoft.com/help/4019916
3Centre de réponse de sécurité MicrosoftDerniers avis de sécurité et informations sur les vulnérabilitéshttps://msrc.microsoft.com
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