When using Snyk Code static analysis to detect SQL injection vulnerabilities in C#, it is important to note that Snyk Code won’t detect a custom SQL injection mitigation that validates dynamic column names against a Regex unless there is a local Regex variable declaration. The actual Regex can be statically defined elsewhere, but there needs to be a local reference to it in order for Snyk to detect that attack vectors were successfully mitigated.

Example Code

Here is an example of the code that demonstrates the issue:

using System;
using System.Data.SqlClient;
using System.Text.RegularExpressions;

public class SqlInjectionMitigation
{
    private static readonly Regex ColumnNameRegex = new Regex("^[a-zA-Z0-9_]+$");

    public void ExecuteQuery(string columnName)
    {
        if (!ColumnNameRegex.IsMatch(columnName))
        {
            throw new ArgumentException("Invalid column name");
        }

        string query = $"SELECT {columnName} FROM Users";
        using (SqlConnection connection = new SqlConnection("your_connection_string"))
        {
            SqlCommand command = new SqlCommand(query, connection);
            connection.Open();
            SqlDataReader reader = command.ExecuteReader();
            while (reader.Read())
            {
                Console.WriteLine(reader[0]);
            }
        }
    }
}

In the above code, the ColumnNameRegex is defined as a static readonly field. However, Snyk Code static analysis won’t detect the custom SQL injection mitigation because there is no local Regex variable declaration.

Solution

To ensure that Snyk Code detects the custom SQL injection mitigation, you need to add a local Regex variable declaration. Here is the modified code:

using System;
using System.Data.SqlClient;
using System.Text.RegularExpressions;

public class SqlInjectionMitigation
{
    private static readonly Regex ColumnNameRegex = new Regex("^[a-zA-Z0-9_]+$");

    public void ExecuteQuery(string columnName)
    {
        // Local Regex variable declaration
        Regex localColumnNameRegex = ColumnNameRegex;

        if (!localColumnNameRegex.IsMatch(columnName))
        {
            throw new ArgumentException("Invalid column name");
        }

        string query = $"SELECT {columnName} FROM Users";
        using (SqlConnection connection = new SqlConnection("your_connection_string"))
        {
            SqlCommand command = new SqlCommand(query, connection);
            connection.Open();
            SqlDataReader reader = command.ExecuteReader();
            while (reader.Read())
            {
                Console.WriteLine(reader[0]);
            }
        }
    }
}

By adding the local Regex variable declaration Regex localColumnNameRegex = ColumnNameRegex;, Snyk Code static analysis will now detect the custom SQL injection mitigation and recognize that the attack vectors have been successfully mitigated.