Decoding SQL Injection and How to Prevent It

Decoding SQL Injection and How to Prevent It

A recent report claimed that as much as 70% of applications contain at least one vulnerability within five years of production. In fact, in the year 2022 alone, 19% of software claimed vulnerabilities of high or critical severity. 

In the constantly changing realm of security, grasping and addressing threats has become essential for every business. Among the myriad vulnerabilities in web applications, SQL injection stands out as a particularly prevalent and potentially harmful cyber security issue. 

This makes us wonder: How can we stop it from happening? 

Let’s dive in to explore the intricacies of SQL injection, look at how attackers exploit this weakness, and provide effective strategies to prevent these kinds of attacks.

What Is SQL Injection?

SQL Injection can be defined as a code injection technique that attackers use to manipulate an application’s database by injecting malicious SQL code into user inputs. It allows unauthorised access to databases, potentially exposing sensitive information, modifying data, or even performing destructive actions. 

Advanced SQL injections can be categorised into three main types. It includes:

  • In-band SQL - Uses database errors or UNION commands.
  • Blind SQL - Exploits the vulnerabilities without receiving direct feedback from the application, making it more challenging to detect.
  • Out-of-band SQL - The attacker retrieves data from the database using a different channel than the one used to inject the malicious code.

Why Is an SQL Injection Attack Performed?

A successful SQL injection can bear severe implications. A few examples of the same include:

  • The virtual credentials of the users can be disclosed to the attackers, which can then be used to impersonate the said individuals.
  • Attackers can gain complete access to the massive amounts of important data in a database server.
  • Attackers might alter data, such as balances, void transactions, or even transfer money to their accounts.
  • With SQL injection, attackers can completely erase all the records from the database, which in turn can affect application availability. Although the option for backup is always present, it does not fully cover the most recent data. 
  • Using SQL injection as the initial vector, attackers can cause severe damage to the internal network behind a firewall.

How to Prevent an SQL Injection Attack?

Mentioned below are some of the most effective techniques by which you can prevent SQL injection vulnerabilities:

Prepared Statements with Parameterised Queries

Prepared statements, also known as parameterised queries, can be a great way to prevent SQL injection attacks. In Python, various database libraries support prepared statements, which include:

  • ‘sqlite3’ for SQLite
  • ‘psycopg2’ for PostgreSQL and
  • ‘mysql-connector-python’ for MySQL.

However, please note that in some cases, prepared statements can harm performance. While the likelihood is minimal, should you ever encounter such a situation, you can explore these methods:

  • Strongly validate all data.
  • Use an escaping routine that aligns with your database vendor to escape all user-supplied input. 

Stored Procedures

A stored procedure functions as a precompiled set of one or more SQL statements, capable of execution as a cohesive unit. This method serves as an effective defence against SQL injection attacks. By encapsulating SQL logic within stored procedures, the vulnerability to direct SQL injection through user inputs is significantly reduced.

However, please note that, in this case, the stored procedure should not include any unsafe dynamic SQL generation. Although developers can generate dynamic SQL into stored procedures, it should be avoided at all costs. 

Allow-List Input Validation

Lastly, allow-list input validation is a powerful strategy for preventing SQL injection attacks. It involves explicitly defining and allowing only certain characters or patterns in user inputs, rejecting anything else. By specifying a set of acceptable values or patterns, you create a ‘whitelist’ that can effectively filter out potentially malicious input. 


By adopting a combination of all these strategies and, most importantly, staying vigilant about secure coding practices, you can significantly reduce the risk of SQL injection vulnerabilities in your Python application. 

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