CVE-2026-67373 in SQL Server
Summary
by MITRE • 09/08/2026
Heap-based buffer overflow in SQL Server allows an authorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 09/08/2026
The vulnerability described constitutes a critical security flaw within Microsoft SQL Server, specifically manifesting as a heap-based buffer overflow condition that can be exploited remotely by authenticated users. This type of defect arises when the application writes more data to a dynamically allocated memory block on the heap than it was originally intended to hold. In the context of database management systems like SQL Server, such overflows often occur during the processing of complex or malformed queries where input validation mechanisms fail to adequately check buffer boundaries before copying user-supplied data into fixed-size memory regions. The presence of this flaw indicates a fundamental lapse in boundary checking logic within the server's query parser or execution engine components responsible for handling network-transmitted SQL commands.
From an operational perspective, the severity of this vulnerability is amplified by its potential impact on system integrity and availability. Because the overflow occurs in heap memory, which is used for dynamic data storage during runtime operations, successful exploitation allows an attacker to overwrite adjacent memory structures or control flow pointers such as function return addresses. This manipulation can lead to arbitrary code execution with the privileges of the SQL Server service account. If the database engine is running under a high-privilege system account, this could result in complete compromise of the underlying operating system and potentially allow lateral movement within the network infrastructure. The fact that an authorized attacker can trigger this condition means that any user with valid credentials to connect to the instance poses a risk if they possess sufficient permissions to execute specific types of queries or stored procedures vulnerable to this overflow.
The technical classification of this flaw aligns closely with Common Weakness Enumeration (CWE) identifiers such as CWE-120, which denotes Buffer Copy without Checking Size of Input Classic Heap-based Overflow, and potentially CWE-787 if the overwrite targets a pointer leading to out-of-bounds write access. In terms of adversary tactics, this vulnerability maps directly to MITRE ATT&CK technique T1190, Exploit Public-Facing Application, as it involves exploiting weaknesses in software that processes external input. Furthermore, depending on how the exploit is delivered and executed, it may also relate to T1203, Exploitation for Client Execution, if the attack vector targets client-side components interacting with the server, or more commonly T1059, Command and Scripting Interpreter, as a subsequent step after gaining initial access through code execution.
Mitigation strategies must prioritize immediate patching of all affected SQL Server instances to the latest cumulative update provided by Microsoft, which includes specific fixes for heap overflow conditions in query processing modules. In environments where immediate patching is not feasible due to maintenance windows or compatibility concerns, network segmentation should be enforced to restrict access to the database server strictly from trusted application servers and administrative workstations using firewalls or virtual local area networks (VLANs). Additionally, implementing strict input validation at the application layer can help filter out malformed SQL statements before they reach the database engine. Enabling advanced auditing features allows for monitoring of unusual query patterns that might indicate exploitation attempts, while adhering to the principle of least privilege ensures that service accounts do not run with unnecessary administrative rights on the host operating system, thereby limiting the blast radius in case a successful exploit occurs.