What is a SQL injection (SQLi)?

A SQL injection (SQLi) is a technique that attackers use to gain unauthorized access to a web application database by adding a string of malicious code to a database query.

A SQL injection manipulates Structured Query Language (SQL) code to provide access to protected resources, such as sensitive data, or execute malicious SQL statements. When executed correctly, a SQL injection can expose intellectual property, customer data, or the administrative credentials of a private business.

SQL injection attacks can be used to target any application that uses a SQL database, with websites being the most common prey. Common SQL databases include MySQL, Oracle, and Microsoft SQL Server.

How does a SQL injection attack work?

A SQL query is a request for some action to be performed on an application database. Queries can also be used to run operating system commands. Each query includes a set of parameters that ensure only desired records are returned when a user runs the query. During a SQL injection, attackers exploit this by injecting malicious code into the query's input form.

The first step of a SQL injection attack is to study how the targeted database functions. This is done by submitting a variety of random values into the query to observe how the server responds.

Attackers then use what they've learned about the database to craft a query the server interprets and then executes as a SQL command. For example, a database may store information about customers who have made a purchase with customer ID numbers. Instead of searching for a specific customer ID, an attacker may insert CustomerID = 1000 OR 1=1 into the input field. Since the statement 1=1 is always true, the SQL query would return all available customer IDs and any corresponding data. This enables the attacker to circumvent authentication and gain administrator-level access.

In addition to returning unauthorized information, SQL attacks can be written to delete an entire database, bypass the need for credentials, remove records, or add unwanted data.

How many types of SQL injection attacks are there?

There are a few different types of SQL injection attacks.

1. In-band SQLi

Also known as classic SQLi, in-band SQLi is when hackers use the same channel -- or band -- to launch database errors and to collect the results from an attack. In-band SQLi is most commonly achieved through two methods:

1. Error-based injection techniques force the database to produce error messages that reveal information about the structure of the database.
2. Union-based attacks use prepared statements that exploit the SQL union function, which combines the results of multiple queries into one result.

2. Inferential SQLi

Also known as blind SQLi, inferential SQLi is when hackers send data payloads to a database server to observe its response and behavior without being able to see what is occurring within the database. The server's response provides attackers with clues that they can use to adjust their attack strategy.

Inferential SQLi can be either boolean-based (using true or false statements to solicit a response) or time-based (setting a designated response period).

3. Out-of-band SQLi

Out-of-band SQLi is when hackers take advantage of domain name system (DNS) or Hypertext Transfer Protocol (HTTP) requests to retrieve data. Out-of-band SQLi is usually only performed when a web server is too slow or when in-band SQLi is not possible to execute.

How can a SQL injection attack be detected and prevented?

If a SQL injection attack is successfully carried out, it could cause extensive damage by exposing sensitive data and damaging customer trust. That's why it is important to detect this type of attack in a timely manner.

Web application firewalls (WAFs) are the most common tool used to filter out SQLi attacks. WAFs are based on a library of updated attack signatures and can be configured to flag malicious SQL queries in web applications.

To prevent a SQL injection attack from occurring, businesses can follow these practices:

• Train employees on prevention methods: It's important that IT teams -- including DevOps, system administrators, and software development – receive proper security training to understand how SQLi attacks happen and how they can be prevented.
• Don't trust user input: Any user input provided in a SQL query increases the likelihood for a successful SQL injection. The best way to mitigate this risk is to put security measures around user input.
• Use an allowlist instead of a blocklist: Validating and filtering user input via an allowlist is recommended because cybercriminals can usually bypass a blocklist. Blocklists are hard to keep updated against zero-day vulnerabilities.
• Perform routing updates & use newest versions: Outdated software and older programming languages are more vulnerable. For example, use PHP Data Objects (PDO) as a substitute for older MySQL functions.
• Use validated prevention methods: The best way to protect web applications is through input validation, prepared statements, and parameterized queries.
• Perform regular security scans: Regularly scanning web applications catches and remedies potential vulnerabilities before they do serious damage.

The impact of SQL injection attacks for your business

SQL injection attacks can seriously harm a business or organization. The negative effects could include the following:

• Cybercriminals could gain unwanted or administrative access to private information and resources.
• Potential data breaches can occur as a result of unauthorized access.
• Data can be altered, or entire database tables can be deleted.
• Database infiltration can enable threat actors to penetrate entire networks.
• Customers may lose trust in the business, leading to decreased revenue.
• Long-term damage caused by reputation loss, legal costs, and lost business opportunities.

A few well-known companies that have experienced SQL injection attacks include Target, Yahoo, LinkedIn, Sony Pictures, and 7-Eleven.

Examples of SQL injection attacks

There are numerous SQL injection vulnerabilities, attacks, and strategies. The following are some common examples:

• Changing SQL query: Cybercriminals change the query to reveal hidden data.
• Login bypass: Injecting a SQL command into a login form to get around authentication.
• Undermining application logic: Altering a query to obstruct the logic of the application.
• Union attacks: Retrieving data from many database tables.
• Database analysis: Analyzing the database to glean information about its version and structure.
• Distributed denial of service (DDoS): Injecting a SQL statement to overwhelm a system.

Real-life SQL injection vulnerabilities

• Tesla (2014): Researchers penetrated Tesla's website via SQLi to get administrative privileges and steal user data.
• Fortnite (2019): A vulnerability was discovered that could enable attackers to access user accounts (later patched).
• Cisco (2018): A vulnerability in Cisco Prime License Manager enabled attackers to get shell access.

History of SQL injections

SQL injection attacks have been around for over two decades since they were first documented by cybersecurity researcher and hacker Jeff Forristal in 1998. However, they didn't appear to get much attention until 2002.

These attacks have now become one of the most common and continuously rated top security exploits in database software history.

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~ SHUBHAM