CVE-2026-47295: SQL Injection and Privilege Escalation in Microsoft SQL Server

Microsoft SQL Server depends on various built-in system stored procedures, system catalog views, and administrative scripts to coordinate engine metadata, facilitate internal operations, and expose schema instrumentation. These procedures often execute under highly privileged security contexts, such as the system administrator (sa) account, using EXECUTE AS clauses to perform privileged server-level changes on behalf of unprivileged callers.

The attack surface exists in the Tabular Data Stream (TDS) endpoint, which represents the primary communication channel for SQL queries. An authenticated network user with basic session access (such as members of the public server role) can interact with specific, exposed system procedures. If these procedures do not safely handle input parameter boundaries, they allow arbitrary command sequences to be evaluated.

This vulnerability is classified as a severe SQL Injection vulnerability (CWE-89) within internal database routines. Unlike application-level SQL injection that aims to extract business database tables, this flaw operates within the internal database engine itself, allowing callers to bypass internal permission-checking gates.

The root cause of CVE-2026-47295 is the improper neutralization of special elements within internal system stored procedures that utilize dynamic T-SQL compilation. When these procedures construct commands dynamically by concatenating user-supplied arguments (such as schema identifiers, physical table names, or index values), they create a execution flow where SQL statements are parsed twice: once during the procedure invocation and once during dynamic execution.

The database engine processes these parameters without applying safe escaping or parameterized interfaces. Because the system procedure runs with elevated security definitions (such as EXECUTE AS OWNER or EXECUTE AS 'sa'), any commands appended to the parameter inherit the highly privileged context. This execution inheritance enables the payload to bypass standard Role-Based Access Control (RBAC) mechanisms enforced on standard database tables.

The dynamic parsing engine fails to differentiate between the structural code of the system procedure and the data supplied by the caller. Consequently, the SQL parser interprets injected operators, such as single-quote literal boundaries, semicolons, and comment marks, as instruction boundaries. The diagram below illustrates this privilege escalation process:

Due to the closed-source architecture of Microsoft SQL Server, researchers reconstruct the code-level flaw using T-SQL equivalents of the vulnerable internal routines. The vulnerable implementation concatenates the user input directly into a dynamic string before submitting it to the EXEC or sp_executesql engine:

-- Vulnerable Dynamic SQL Pattern in System Procedure
CREATE PROCEDURE sys.sp_vulnerable_internal
    @input_table_name NVARCHAR(256)
WITH EXECUTE AS 'sa'
AS
BEGIN
    DECLARE @sql NVARCHAR(MAX);
    -- VULNERABILITY: Direct string concatenation of user-supplied parameter
    -- This allows an attacker to break out of the string boundary using a single quote
    SET @sql = N'SELECT * FROM sys.objects WHERE name = ''' + @input_table_name + N'''';
    
    EXEC sp_executesql @sql;
END;

The security patch remediates this flaw by redesigning the Dynamic SQL compilation. Rather than concatenating parameters into the query structure, the engine utilizes strict parameterization inside the sp_executesql arguments or wraps input parameters with safety helpers such as the QUOTENAME() function, preventing execution of nested operations:

-- Patched Dynamic SQL Pattern using Parameterization
CREATE PROCEDURE sys.sp_vulnerable_internal
    @input_table_name NVARCHAR(256)
WITH EXECUTE AS 'sa'
AS
BEGIN
    DECLARE @sql NVARCHAR(MAX);
    -- REMEDIATION: The variable is kept as a strict parameter operand (@name)
    -- This ensures the query parser treats the input purely as data, not code
    SET @sql = N'SELECT * FROM sys.objects WHERE name = @name';
    
    EXEC sp_executesql @sql, N'@name NVARCHAR(256)', @name = @input_table_name;
END;

The fix is complete and robust because it shifts the evaluation model from dynamic evaluation to parameterized execution, which systematically neutralizing structural input variations.

To successfully exploit this vulnerability, an attacker must first obtain a valid login on the target SQL Server instance. The attacker does not require high-level permissions; any low-privileged database user with execution privileges on the affected internal system stored procedure is sufficient. The attack is executed over a network via standard database connection tools or application proxy configurations.

The execution payload is structured to close the open string literal, inject a distinct secondary administrative transaction, and comment out the trailing characters of the original query. The objective is typically to add the attacker's login to the sysadmin server role, granting complete administrative control over the database engine:

-- Conceptual Exploitation Input Payload
SELECT name FROM sys.objects;
EXEC sp_addsrvrolemember 'attacker_login', 'sysadmin'; --

When the system procedure receives this input, the dynamic query is assembled into an execution block containing the administrative promotion instruction. Because the procedure utilizes EXECUTE AS 'sa', the database engine executes the role membership modification with full administrative authorization, succeeding without raising security permission checks.

Successful exploitation of CVE-2026-47295 leads to complete administrative compromise of the affected Microsoft SQL Server instance. An attacker who elevates their privileges to sysadmin gains full control over all databases hosted on the instance, including read, write, and delete permissions on any transactional table or system configuration value.

The confidentiality, integrity, and availability of database assets are completely compromised. Attackers can export sensitive business records, modify audit configurations, establish persistent administrative backdoors, or delete data structures, causing operational disruption.

While the scope remains within the database instance (S:U), achieving sysadmin level control frequently allows attackers to leverage advanced features such as xp_cmdshell or SQL Server Agent jobs to run command-line actions on the underlying host operating system. This represents a significant pathway for host network lateral movement.

The primary remediation strategy is the immediate application of official Microsoft security updates. These patches are available through General Distribution Releases (GDR) and Cumulative Updates (CU) for all supported SQL Server versions, from SQL Server 2016 SP3 up to SQL Server 2025.

In environments where patches cannot be instantly applied, security teams must deploy network-level and host-level detection controls. Security professionals should implement auditing rules to log modifications to server role memberships, specifically looking for additions to the sysadmin role:

-- Monitor for server role membership changes
CREATE SERVER AUDIT [Audit_Role_Escalations]
TO FILE (FILEPATH = 'C:\SQLAudit\');
CREATE SERVER AUDIT SPECIFICATION [Spec_Role_Escalations]
FOR SERVER AUDIT [Audit_Role_Escalations]
ADD (SERVER_ROLE_MEMBER_CHANGE_GROUP);
ALTER SERVER AUDIT [Audit_Role_Escalations] WITH (STATE = ON);

Additional defensive mitigations include applying the principle of least privilege by revoking public execution rights on unused system stored procedures and enforcing strict network controls to isolate SQL Server ports (TCP 1433 and UDP 1434) from untrusted segments.