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What is SQL Injection?

SQL Injection has become a common attack vector against database-driven websites; it is easily noticed and exploited. Throughout this article, we will discuss what SQL Injection is, what types of SQL Injections are there, how websites become vulnerable to the injection, and lastly, the mitigation of the vulnerability.

SQL Injection (SQLI)

SQL Injection (SQLi) is a web security vulnerability that allows a malicious actor to inject malicious SQL statements in the queries an application makes to its database. It permits unauthorized entities to view data to which they should not have access, like other users’ information or any other data that the application can access. An attacker can modify or delete the data, forcing constant changes to the application’s content or behavior. SQL Injection can also lead to additional damages, such as compromising the underlying server or back-end infrastructure.  

Types of SQL Injection

Several SQL injection attacks exist and are categorized based on the techniques used to access the information and the potential harm:

  • In-Band SQLi occurs when an unauthorized entity can use the same communication channel for querying the database and gathering information.
  • Error-based SQLi occurs when the database’s details and structure are collected on the errors returned.
  • Union-based SQLi happens when the union operator can be used to return the results of several SQL statements as part of the HTTP response.
  • Inferential (Blind) SQLi occurs when no response is shown on the application itself, but deductions about the database construct can be made based on the server’s behavior.
  • Boolean-based SQLi occurs when queries that will result in a True or False value are used to check if the HTTP responses are changing or not.
  • Time-based SQLi is based on the delay time of the HTTP response. Based on the time it takes for this response to return, it can be known whether the query was executed correctly.
  • Out-of-band SQLi occurs when an unauthorized entity cannot use the same channel to launch the attack and gather results. The attacker can only use this method when specific features are enabled on the database server used by the web application.

Input fields are always tested for SQL injection or XSS scripting vulnerabilities because the data entered by clients should be handled in the back-end of the website. When the data isn’t appropriately sanitized, meaning the developers did not escape unique characters or handle input accurately, explicit queries can be embedded in the input field, causing undesirable application behavior. In the case of SQL injections, adding Structured Queries in the input field might cause a database leak. The simplest method for testing an application for potential leaks is by inserting a single quote, which will break the code login in the back-end, leaving the query uncompleted and causing a SQL error to show.

Consequences of SQL Injection (Data)

In the cybersecurity world, the Confidentiality, Integrity, and Availability of data are of most importance. If an attacker successfully exploits a SQL Injection vulnerability, the confidentiality and integrity of the data will automatically be lost. Furthermore, it can also impact Authentication and Authorization since the attacker via queries can delete or change the data of a specific user. Another huge impact of SQL Injection is the loss of trustworthiness and reputation of the breached company. Users who get affected are less likely to trust the company with their data again. 

Some other actions SQL Injection permits the attacker to do are: 

  • Download unauthorized data
  • Destroy backups
  • Monitor systems
  • Encrypt data


Why am I vulnerable to SQL Injection?

Unpatched Applications

Utilizing the latest software versions is critical to avoid security exploits, like SQL Injection. Continually monitoring for new security vulnerabilities and responding as required is essential to avoid unnecessary situations. 

Validation and Sanitize

The lack of sanitizing and validating can easily lead to SQLi; escaping special characters when developing a web application is essential. For example, the apostrophe (single quote) character is vital for SQL Injection since it will break the database logic.

  • Validation is the method of inspecting if the input fulfills a set of standards.
  • Sanitization is modifying the input to ensure that it is valid.

Error Handling

Users with no malicious intentions usually ignore an error, but malicious actors value errors, especially web application errors, where an attacker can learn more about the application through the error. So it is essential to employ proper error handling and never show errors on the client-side.


Mitigation of SQL Injection

Parameterized Queries

Parameterized queries are a mechanism of pre-compiling a SQL statement to provide the parameters for the statement to be executed. This method makes it possible for the database to identify the code and differentiate it from input data. 

With parameterized queries, when a SQL query is sent, the database knows what it will do, and it will only insert the username and passwords as values. Let us assume the attacker tries the notorious ” OR 1=1′–“, the query, in this case, would look for a username of “OR 1=1′–” and no password, which will result in the query not being executed and an error is thrown. 

Validation and Sanitization

Sanitizing data is the process of converting all characters to “harmless” encoded characters so that dangerous symbols don’t pass through directly to the query. The validation method seeks to confirm whether or not the type of input submitted by a user is permitted. It helps neutralize any commands inserted in the input string; only the value which passes the validation can be processed.

Stored Procedures

Stored Procedures add a security layer to the database. It serves the escaping needed for the application to treat the input as data to be operated on rather than SQL code to be executed.

The idea of stored procedures is that the SQL code is written and stored in the database server. Then whenever needed to execute the query, you can call the stored procedure instead of writing it repeatedly.

Note: SQL Injection can occur if the dynamic SQL inside the stored procedure is not handled correctly.