Critical Flaw in Microsoft SQL Server Opens Door to Remote Code Execution

A critical heap-based buffer overflow vulnerability, identified as CVE-2025-49717, has been discovered in Microsoft SQL Server, posing a significant security risk to organizations. The flaw, which received a high severity CVSS score of 8.5, could allow an authenticated attacker to execute arbitrary code remotely on affected systems.

The vulnerability was addressed by Microsoft as part of its July 2025 Patch Tuesday updates. Successful exploitation of this vulnerability could lead to a complete compromise of the SQL Server, potentially allowing an attacker to view, change, or delete data, create new accounts with full user rights, and even execute code on the underlying operating system.

Understanding the Threat: Heap-Based Buffer Overflow

CVE-2025-49717 is a heap-based buffer overflow, a type of memory corruption vulnerability. It occurs when a program writes data beyond the boundaries of a reserved memory block on the heap, a region of memory used for dynamic memory allocation. In the case of this vulnerability, a specially crafted SQL query can be sent by an authenticated attacker to trigger the overflow, leading to a scenario where the attacker can execute malicious code.

While the vulnerability requires an attacker to be authenticated, the required privilege level is low. However, Microsoft has assessed the attack complexity as "high," indicating that an attacker would need to perform preparatory actions on the target environment before launching an attack. It is also suggested that this vulnerability could be chained with other information disclosure vulnerabilities, such as CVE-2025-49718 and CVE-2025-49719, which were also patched in the July 2025 update. These related flaws could help an attacker gather information to prepare for the main attack.

Affected Microsoft SQL Server Versions

The security flaw affects the following versions of Microsoft SQL Server:

  • Microsoft SQL Server 2019 (GDR and CU releases)
  • Microsoft SQL Server 2022 (GDR and CU releases)

Microsoft has released specific updates for each affected version to remediate the vulnerability. For example, the security update for SQL Server 2022 GDR is detailed in knowledge base article KB5058712.

Mitigation and Best Practices

The primary and most crucial step for mitigation is to apply the security updates released by Microsoft in the July 2025 Patch Tuesday.

In addition to patching, organizations are advised to follow these security best practices to minimize their risk:

  • Principle of Least Privilege: Ensure that accounts that can access the SQL Server have only the minimum necessary permissions.
  • Network Segmentation and Firewalls: Restrict network access to the SQL Server to only trusted hosts and networks.
  • Regular Monitoring: Continuously monitor SQL Server logs for any suspicious activity or unauthorized access attempts.
  • Stay Informed: Keep abreast of the latest security advisories from Microsoft and other security organizations.