Critical Remote Code Execution Vulnerability in Microsoft SQL Server (CVE-2026-20810)

Microsoft Security Response Center has assigned CVE-2026-20810 a CVSS base score of 9.8 (Critical). The vulnerability enables remote code execution through specially crafted network requests to SQL Server instances. Attackers can exploit this without any user interaction or credentials.

Affected versions include SQL Server 2019 (all builds prior to 15.0.4385.2), SQL Server 2017 (all builds prior to 14.0.2050.1), SQL Server 2016 (all builds prior to 13.0.6435.1), and SQL Server 2014 (all builds prior to 12.0.6449.1). The vulnerability impacts both default instances and named instances. It also affects SQL Server on Windows and Linux platforms.

The flaw resides in the SQL Server Database Engine service. The service fails to properly validate incoming RPC requests before processing them. This allows buffer overflow conditions that lead to arbitrary code execution in the context of the SQL Server service account. The service typically runs with elevated privileges, making successful exploitation particularly dangerous.

Exploitation requires network access to the SQL Server port (default 1433). No authentication is needed. This makes internet-facing SQL Server installations immediate targets. Shodan shows over 1.2 million SQL Server instances exposed to the internet globally.

Microsoft has released security patches for all affected versions. Administrators should apply updates immediately:

• SQL Server 2019: Build 15.0.4385.2 or later (KB5034123)
• SQL Server 2017: Build 14.0.2050.1 or later (KB5034122)
• SQL Server 2016: Build 13.0.6435.1 or later (KB5034121)
• SQL Server 2014: Build 12.0.6449.1 or later (KB5034120)

If immediate patching is not possible, implement these mitigations:

1. Block TCP port 1433 at network firewalls. Restrict access to only authorized application servers.
2. Disable SQL Server Browser service if not required.
3. Enable Windows Firewall on all SQL Server hosts. Configure rules to allow only necessary connections.
4. Use IPsec policies to restrict network access to SQL Server instances.
5. Consider disabling RPC endpoints if your applications use only TDS protocol.

Verify exploitation attempts by monitoring SQL Server error logs for entries containing "access violation" or "fatal error" messages. Check Windows Event Logs for SQL Server service crashes. Network monitoring tools can detect anomalous RPC traffic patterns.

This vulnerability shares characteristics with previous SQL Server RCE flaws such as CVE-2019-0658 and CVE-2020-0618. The pattern of unauthenticated network-based attacks against database services continues to present major security challenges for enterprise IT.

Organizations running Microsoft SQL Server should prioritize this patch cycle. The combination of remote execution, no authentication requirement, and widespread internet exposure creates a perfect storm for potential mass exploitation. Historical data shows that similar SQL Server vulnerabilities are typically exploited within 7-14 days of patch release.

For additional technical details and verification steps, refer to the Microsoft Security Update Guide and SQL Server security documentation.