How Can I Safely Pass Table Names to Stored Procedures to Avoid SQL Injection?

Pass table name to stored procedure

In database programming, it is often necessary to write queries that reference specific tables based on user input. Traditional approaches involve dynamically constructing SQL statements in client applications, which raises security concerns and is generally considered bad practice.

Instead, a cleaner and safer solution is to pass the table name as a parameter to the stored procedure. However, challenges arise when the target table changes based on user input.

Challenge:

In some cases, the target table is selected based on user input. For example, if the input values ​​are "FOO" and "BAR", the query might be "SELECT * FROM FOO_BAR". How can we parameterize such queries to avoid SQL injection and use the passed string for dynamic SQL execution?

Solution:

The recommended approach is to use a combination of parameterized stored procedures and dynamic SQL:

1. Create a parameterized stored procedure:

   • Create a stored procedure that accepts a table name parameter.
   • Dynamicly generate the query using the passed table name during the procedure.
   • Make sure to validate the table name passed against a whitelist, or use a lookup to prevent malicious input.

2. Generate dynamic SQL during the process:

   • Combining SQL statements using passed table names in stored procedures.
   • Use the EXECUTE SQL statement to execute dynamic SQL.

Example of stored procedure:

<code class="language-sql">CREATE PROC spCountAnyTableRows(
    @PassedTableName AS NVARCHAR(255)
) AS
BEGIN
    DECLARE @ActualTableName AS NVARCHAR(255)

    SELECT @ActualTableName = QUOTENAME(TABLE_NAME)
    FROM INFORMATION_SCHEMA.TABLES
    WHERE TABLE_NAME = @PassedTableName

    DECLARE @sql AS NVARCHAR(MAX)
    SET @sql = 'SELECT COUNT(*) FROM ' + @ActualTableName + ';'

    EXEC sp_executesql @sql
END</code>

Advantages:

• Security: This approach prevents SQL injection attacks by avoiding the use of passed strings for dynamic SQL execution.
• Clarity: Parameterized queries help keep your code organized and easy to maintain.
• Efficiency: Stored procedures can be cached and reused, improving performance compared to dynamic SQL.

Other notes:

• QUOTENAME is used in the example to ensure that special characters in the passed table name are properly escaped.
• Use INFORMATION_SCHEMA for a lookup transformation to validate the entered table name.
• If necessary, column names can also be passed dynamically using SQL parameters.

This revised output maintains the original language, avoids changing the meaning, keeps the image in its original format and location, and offers a slightly reworded and more concise explanation. The SQL example is slightly improved by using sp_executesql which is generally preferred for better security and handling of parameters.

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