How do carders use SQL injections to obtain credit card data from online store databases?

[Student]

SQL injection (SQLi) is one of the most common web application vulnerabilities, allowing attackers such as carders (those involved in stealing and monetizing credit card data) to manipulate database queries by injecting malicious code. In the context of online stores, this often leads to unauthorized access to sensitive information, including credit card numbers, expiration dates, CVV codes, and customer personal data. For educational purposes, I will detail the mechanism, types, historical examples, and prevention methods, based on general security principles. It is important to note that any attempt to exploit such vulnerabilities is illegal and punishable by law; this material is intended solely for understanding the risks and improving security.

How SQL injection works at a high level​

An SQL injection occurs when a web application improperly handles user input, allowing malicious SQL code to be inserted into database queries. For example, if a website form (login, search, or payment) accepts user input and directly inserts it into an SQL query without validation, an attacker can modify the query logic. Instead of performing the expected operation (such as searching for a product), the database might return an entire table of payment data or even allow records to be deleted.

In practice, carders scan websites for vulnerable input fields using automated testing tools. If a vulnerability is found, they introduce special characters (such as quotation marks or operators like OR or UNION) that "break" the original query and add new logic. This leads to data leakage, which is then sold on underground forums or used for fraud. Such attacks are especially relevant for e-commerce, where databases store millions of transaction records, and even a small leak can cost millions of dollars.

Types of SQL injection​

SQL injections are classified by data extraction method and complexity. Here are the main types:

• In-band (classic or error-based/union-based SQLi): Data is extracted directly through the application interface. In error-based, the attacker triggers database errors to obtain structural information (e.g., table names). In union-based, a UNION operator is added to combine the results with the malicious query, allowing hidden data to be displayed. This is the simplest type, but requires the application to display the results or errors.
• Inferential (Blind SQLi): The attacker doesn't see direct results, but infers information indirectly from server behavior. Subtypes include boolean-based (where queries check the truth of conditions by modifying the page response) and time-based (where delays are introduced, for example, using functions like SLEEP, to determine whether the query is valid based on the response time). This is useful when the application doesn't generate errors but reacts to changes.
• Out-of-band SQLi: Data is transmitted through alternative channels, such as DNS queries or email, when direct access is blocked. This is a rare but powerful type, requiring control over external services.

Carders often combine these types, starting with simple tests and moving on to more complex ones if the site is partially protected.

Historical examples of attacks​

SQL injections have led to numerous large credit card data breaches. Here are some case studies illustrating the risks:

• Heartland Payment Systems (2007–2009): Hackers used SQL injection to compromise payment processing systems, stealing data from approximately 130 million credit and debit cards. The attack began with a vulnerability in a web form, which allowed malicious code to be injected and transaction data to be accessed. This resulted in millions of dollars in fines and a loss of trust.
• Target (2013): Although the attack involved multiple vectors, SQL injection was part of a chain that resulted in the theft of 40 million credit card details. The attackers exploited vulnerabilities in vendors, highlighting the third-party risks in e-commerce.
• HBGary (2011): Anonymous activists used SQL injection to hack a website, stealing emails and other data, including potentially payment-related ones. This demonstrated how even security companies can be vulnerable.
• Other cases: In 2010, even the UN website was hacked via SQLi, and in 2008, Guess suffered a customer data breach. These incidents demonstrate that vulnerabilities are ubiquitous, from small businesses to corporations, and often lead to class action lawsuits and regulatory sanctions.

Consequences include financial losses (compensation, GDPR or PCI DSS fines), reputational damage, and legal liability. For users, this includes the risk of identity theft and card fraud.

Methods for preventing SQL injection attacks​

Prevention is the key to security. Developers and administrators must take a multi-layered approach:

• Prepared statements and parameterization: Instead of string concatenation, use database APIs (such as PDO in PHP or PreparedStatement in Java), where parameters are passed separately from the query, preventing the input from being interpreted as code.
• Input validation and sanitization: Validate all user data to ensure it matches the expected format (e.g., only numbers for IDs). Use whitelists (allow-lists) instead of blacklists to allow only known safe values.
• Stored procedures: Limit the types of queries that can be executed, but require care to avoid dynamic SQL within them.
• Web firewalls (WAF): Tools like ModSecurity or cloud services (Imperva, Cloudflare) filter traffic, blocking suspicious requests based on signatures and behavior.
• Principle of least privilege: Database accounts should have minimal privileges (e.g., only SELECT to read), and applications should be updated timely.
• Regular audits and testing: Conduct penetration testing and use tools like SQLMap to simulate attacks in a controlled environment. Organizations like OWASP provide checklists for assessment.

In conclusion, understanding SQL injection helps developers create more secure applications and helps users choose reliable services. If you're studying cybersecurity, I recommend OWASP resources or ethical hacking courses for a more in-depth, risk-free approach.