What Is SQL Injection Attack?

By on September 23, 2021

Learn about SQL injection attack concepts, types, alerts, and detection and prevention mechanisms.

  • SQL Injection Definition
  • How Does SQL Injection Work?
  • What Is an Example of SQL Injection?
  • What Are the Different Types of SQL Injection Attacks?
  • How to Prevent SQL Injection Attacks
  • How to Stop a SQL Injection
  • What Is SQL Injection Attack?

    SQL injection (SQLi) is a highly prevalent attack vector that employs malicious SQL statements to attack data-driven web applications by exploiting SQL code vulnerability. Attackers maneuver SQL injection vulnerabilities to get unauthorized access to database servers, hamper back-end processes, and alter or delete sensitive business data and information.

    How Does SQL Injection Work?

    To understand how SQL injection works, it’s essential to know what a structured query language (SQL) is. SQL is a query language used in programming to access, modify, and delete data stored in relational databases. Since most websites and applications use SQL databases to store data and employ SQL commands to execute operating system commands, a SQL injection attack may result in grave business consequences.

    Attackers begin with identifying vulnerable user inputs in a web application using a SQL database such as SQL Server, MySQL, and Oracle, among others because applications with SQL injection vulnerability leverages such user input to execute malicious SQL statements. Next, the attackers create and send malicious content to the SQL server to execute malicious SQL commands and hamper the database. Businesses may witness detrimental impacts of a successful SQL injection as attackers use such attacks for the following purposes:

    • Impersonating database users, including database administrators, by discovering their credentials to access the database.
    • Gaining complete access to data in a database server.
    • Adding, modifying, or deleting data in a database. Such data alteration may severely impact businesses and hamper data security.
    • Exploiting sensitive business data, including customer information, financial data, intellectual property, and more.
    • Accessing the operating system via the database server to attack the internal network by breaching a firewall.

    What Is an Example of SQL Injection?

    Attackers planning to execute a SQL injection try manipulating a standard SQL query by exploiting non-validated input vulnerabilities in a database. There are several ways to execute such attacks; the following example gives a basic idea of how SQL injection works.

    This example shows how attackers may exploit concatenation weakness. The code below results in the current username and searches for items matching a specific item name, where the owner is the current user.

    string userName = ctx.getAuthenticatedUserName();
    string query = "SELECT * FROM items WHERE owner = "'"
                    + userName + "' AND itemname = '"
                    + ItemName.Text + "'";

    On combining the username and item name, you get the following query:

    SELECT * FROM items 
    WHERE owner =
    AND itemname = ;

    The challenge, in this situation, is the original code uses concatenation to combine data. 

    The attacker may use a string such as ‘name’ OR ‘a’=’a’ as the item name. The condition ‘a’=’a’ always evaluates to true. Hence, the SQL statement will hold true for every item in the table. 

    Now the SQL statement changes to the following:

    SELECT * FROM items
    WHERE owner = 'john'
    AND itemname = 'name' OR 'a'='a';

    To put it simply, it’s the same as SELECT * FROM items;

    Therefore, the above query will return the data of the entire table, giving the attacker unauthorized access to sensitive data.

    What Are the Different Types of SQL Injection Attacks?

    There are three broad categories to classify SQL injections, depending on the methods they use to gain access to back-end data and the extent of the potential damage they can cause.

    1. In-band SQLi: This SQLi attack type is simple and efficient to execute for attackers. In this case, the attacker uses the same communication channel to launch attacks and gather results. This type of SQLi attack has the following two sub-variations:

    • Error-based SQLi: Here, the database produces an error message as a result of the attacker’s actions. The attacker then gathers the database infrastructure information based on the data generated by these error messages.
    • Union-based SQLi: When the attacker leverages the UNION SQL operator to get the desired data by fusing multiple select statements in a single HTTP response, it’s known as union-based SQL injection.

    2. Inferential SQLi: In this type of SQLi, the attackers use the response and behavioral patterns of the server post-sending data payloads to learn more about its structure. Since, in this case, data doesn’t transfer from the website database to the attacker, the attacker doesn’t get to see information about the attack in-band. Inferential SQLi can be further classified into two sub-types:

    • Time-based SQLi: Here, attackers send a SQL query to the database, making the database wait (in seconds) before it finally responds to the query as true or false.
    • Boolean SQLi: Here, attackers send a SQL query to the database, letting the application respond by generating either a true or false result.

    3. Out-of-band SQLi: This type of attack is executed under two circumstances—when attackers can’t use the same channel to launch the attack as well as gather information or when a server is either very slow or unstable to perform these actions.

    How to Prevent SQL Injection Attacks

    SQL injection prevention can be tough for businesses as implementing specific techniques depends on multiple factors. It’s critical to consider the underlying sub-category of SQL injection vulnerability, type of SQL database engine, and the programming language used for the web applications. However, organizations should follow some basic principles to help defend their websites and web applications. 

    • Create awareness about the SQLi-based risks within the team involved in building the web application and provide necessary role-based training to all the users to deal with such challenges.
    • Keep user input in check, as any user input used in a SQL query introduces risk. Address input from authenticated and/or internal users in the same manner as public input until it’s verified.
    • Use whitelists as a standard practice instead of blacklists to verify and filter user input.
    • Adopt the latest version of the development environment and language to help ensure effective protection, as older versions lack current safety features.
    • Continuously scan web applications using comprehensive application performance management tools.

    How to Stop a SQL Injection Attack

    Businesses must have a strategic plan to proactively stop any data breach attempts through SQL injection attacks because delays in response may result in irreparable damage. Thwarting sophisticated SQL injection attempts require organizations to be prepared and execute appropriate preventive measures without halting business functions.

    The following steps can help businesses detect, analyze, and respond on time to stop SQL attacks.

    • Detect Vulnerabilities: Continuous scanning and testing web applications help discover code vulnerabilities. It’s effective to benchmark events and proactively trace anomalous events.
    • Remediate Vulnerabilities: Once vulnerabilities are identified, it’s imperative to promptly fix them to ensure web application integrity. Some effective measures include sanitizing input before passing it to the database, applying regular security patches, and using parameterized queries rather than dynamic queries.

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