What is SQL Injection and How to Prevent This Attack?

SQL Injection is one of the most dangerous vulnerabilities for websites and online applications. It occurs when a user adds untrusted data to a database query, for example, when filling out a web form. 

If data injection is enabled, attackers can create user input to steal valuable data, bypass authentication, or corrupt records in your database.

 There are different types of SQL injection attacks, but in general, they all have a similar cause. Untrusted data that the user enters is concatenated with the query string. 

Therefore, user input can change the original intent of the query and lead to numerous security issues. 

In this article, we cover and recommend some best practices for technicians to use in preventing SQL Injection attacks. Keep reading and understand more about these practices! 

Do Not Rely on Client-side Input Validation

Client-side input validation is an excellent practice to prevent SQL Injection attacks. With client-side input validation, you can now prevent invalid information from being sent to your system logic. However, this only works for users who have no bad intentions and want to use the system as designed. 

Providing the user with direct feedback that a certain value is not valid is very useful and simple. Therefore, you should use client-side validation to help your user experience. 

When looking at SQL injection, this is not a method you should trust. You can remove client-side validation by changing some Javascript code loaded in your browser. 

Also, it is very easy to make a basic HTTP call to the backend in a client-server architecture with a parameter that causes an SQL injection. Maybe using tools the old-school curl commands.

You should validate the server-side, preferably as close to the source as possible. In this case, you create the SQL query. Anything a client sends you should be considered potentially harmful. So, in this case, relying on client-side validation for SQL injection is a terrible idea.

Use Database Engines With Restricted Privileges

When creating a database user for your application, you should think about this user’s privileges.

Does the application need to be able to read, write and update all databases? How about truncating or dropping tables? If you limit your application’s privileges on the database, you can minimize the impact of SQL injection. 

It is advisable not to have a single database user for your application, but to create multiple database users and connect them to specific application roles with different privileges. Security issues are likely a ripple effect, so you should be aware of all relationships to avoid heavy damage.

Use Ready-made Instructions and Query Parameterization

Many languages have built-in features available that help prevent SQL injection. When writing SQL queries, you can use something like a ready-made statement to compile the query. 

With a ready-made statement, we can perform query parameterization, which is a technique to dynamically create SQL statements. You create the base query with some placeholders and securely attach user-supplied parameters to those placeholders.

When using a real ready-made statement and parameterized queries, the database itself actually takes care of the escape. First, it builds the query execution plan based on the query string with placeholders. 

In the second step, the (untrusted) parameters are sent to the database. The query plan is already created, so the parameters no longer influence this. This avoids the injection completely.

Scan Your Code for SQL Injection Vulnerabilities

Creating custom code is probably easy. However, mistakes are easily made. To verify your code, you can have processes in place, such as code review and pair programming. 

Nevertheless, the person who reviews your pair code with you needs to be well versed in cybersecurity. Regardless, it would be nice to automatically scan your custom code for possible security vulnerabilities.

With the services of some tools, you can automatically inspect your code for security vulnerabilities. This can be easily automated in your system, making it easy to search for “loopholes” used by cybercriminals to break into your structures. 

Run Input Validation

Yes, you must do input validation, always! Although statements prepared with query parameterization are the best defense against SQL injection, always create multiple layers of defense. As well as having limited privileges for a database user, input validation is a great practice to reduce risk to your overall application.

Moreover, there are situations where ready-made statements are not available. Some languages do not support this mechanism, or older database systems do not allow you to provide user input as a parameter. Input validation is an acceptable alternative in these cases.

Make sure that input validation depends on the whitelist and not the blacklist as described above. Create a rule that clearly describes all allowed defaults. 

Be Careful With Stored Procedures

Many people believe that working with stored procedures is a good way to avoid intrusions. This is not always the case. Similar to SQL queries created in your application, a stored procedure can also be maliciously injected. 

Like SQL queries in your application, you must parameterize queries in your stored procedure rather than concatenating parameters. SQL injection into a stored procedure is very easy to prevent.

Make sure you know how to implement stored procedures for your database and be aware of SQL Injections as well.

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