Understanding and Preventing SQL Injection Attacks with C#

SQL Injection continues to be one of the most common and harmful vulnerabilities in web applications. When developing a C# application that connects to a database, it's essential to understand SQL Injection and how to defend against it. In this post, we'll explain what SQL Injection is, how it operates, and share some strategies to safeguard your C# application from this threat.

What is SQL Injection?

SQL Injection happens when an attacker sneaks harmful SQL code into a query. This can let them access, change, or delete data in the database, or even run unwanted commands.

Here’s an example of a vulnerable SQL query in C#:

string query = "SELECT * FROM Users WHERE Username = '" + username + "'";

In this case, if the username input is something like ' OR 1=1 --', the query would become:

SELECT * FROM Users WHERE Username = '' OR 1=1 --';

This would always return true because 1=1 is always true, --' comments out the remainder of the query, potentially bypassing authentication or revealing sensitive data.

How to Prevent SQL Injection in C#

Let’s look at some practical ways you can prevent SQL Injection in your C# applications:

Use Parameterized Queries

The best way to prevent SQL Injection is by using parameterized queries. These queries let you use placeholders in your SQL statements and then safely insert user input as data, not as part of the query itself.

using (var conn = new SqlConnection(connectionString))
{
    var query = "SELECT * FROM Users WHERE Username = @Username";
    var cmd = new SqlCommand(query, conn);
    cmd.Parameters.AddWithValue("@Username", username);

    ...
}

Parameterized queries treat user input as data instead of code, so even if harmful SQL is injected, it won't be executed. Object-Relational Mappers like Entity Framework (EF) automatically handle parameterized queries for you.

Validate and Sanitize User Input

Validating and sanitizing user input remains a best practice, including

• Verifying input matches expected formats (e.g., email, numbers, etc)
• Restricting the length of input
• Rejecting any suspicious characters when possible

Implement Least Privilege

Make sure the database accounts used by the application have only the necessary permissions. For example, avoid using an account with full admin rights for regular queries.

Logging Sensitive Data and Error Handling

Don’t show detailed error messages that include SQL queries or stack traces. These can give attackers valuable information to exploit weaknesses.

By following these best practices, you can greatly reduce the risk of SQL Injection and protect your users' sensitive data.