What is SQL injection? - Web Security Academy

Summary

This video explains SQL Injection (SQLi), a major web security vulnerability where attackers manipulate SQL queries to access, modify, or delete sensitive data. It covers various exploitation techniques, such as bypassing logins, extracting data via the `UNION` keyword, and leveraging blind SQL injection methods like time delays or out-of-band exfiltration. The video also emphasizes SQLi detection using tools like Burp Suite and manual tests. To prevent SQLi, the video stresses using parameterized queries, whitelisting input, and properly handling all user inputs. With practical examples, it illustrates the importance of securing web applications from SQL injection attacks.

Takeaways

• 😀 SQL injection is a web vulnerability that allows attackers to manipulate database queries, potentially exposing, modifying, or deleting data.
• 😀 Attackers can exploit SQL injection to escalate attacks, such as compromising servers or causing denial of service.
• 😀 A typical example of SQL injection involves attackers modifying SQL queries to display hidden or unauthorized data, like unreleased products in an e-commerce app.
• 😀 Blind SQL injection occurs when no error messages are returned, making exploitation harder but still possible through time delays or conditional logic.
• 😀 Union-based SQL injection enables attackers to retrieve data from multiple tables by appending extra queries to a vulnerable SQL query.
• 😀 SQL injection can be used to bypass authentication systems, such as logging in as any user by injecting SQL code into the username field.
• 😀 When discovering SQL injection vulnerabilities, attackers may retrieve database details like version and table structures, aiding further exploitation.
• 😀 Manual testing for SQL injection vulnerabilities includes submitting specific characters or payloads that trigger errors, time delays, or out-of-band network interactions.
• 😀 Blind SQL injection is often harder to detect but can still be exploited using time delays or logic changes, allowing attackers to infer information from application behavior.
• 😀 Prevention of SQL injection is best achieved through parameterized queries, which treat user input as data and prevent it from altering the query structure.
• 😀 Some SQL injection vulnerabilities occur in parts of queries other than the WHERE clause, such as the ORDER BY clause, table/column names, or update/insert statements.
• 😀 Different databases may require specific techniques for detecting and exploiting SQL injection due to variations in syntax, error handling, and query behaviors.

Q & A

What is SQL injection?

SQL injection is a security vulnerability that allows an attacker to manipulate database queries made by a web application. It can enable unauthorized access to data, data modification, and even server or infrastructure compromises.

What type of data can be exposed through SQL injection?

SQL injection can expose sensitive data such as user information, private records, and other data that the application may have access to. This can include data from different users or tables within the database.

How does an attacker exploit SQL injection in a login system?

An attacker can exploit SQL injection in a login system by injecting SQL code, such as a comment sequence (`--`), to bypass password checks. This allows the attacker to log in as any user, even without knowing the correct password.

What is the 'Union' keyword used for in SQL injection attacks?

The 'Union' keyword in SQL injection is used to combine the results of multiple SQL queries into a single response. Attackers can exploit this by appending additional queries to retrieve data from other tables, such as usernames and passwords.

What are 'blind' SQL injection vulnerabilities?

Blind SQL injection occurs when an application does not return errors or detailed database responses. Attackers exploit it by inferring data through timing delays, boolean logic conditions, or out-of-band network interactions.

How can an attacker perform an out-of-band SQL injection attack?

In an out-of-band SQL injection attack, attackers trigger interactions that send data to external systems they control, such as making DNS lookups with the stolen data. This technique works when other methods like time delays or error responses aren't possible.

What tools can be used to detect SQL injection vulnerabilities?

Tools like Burp Suite's web vulnerability scanner can be used to detect SQL injection vulnerabilities. Additionally, manual techniques, such as submitting special characters like single quotes or observing the application’s error responses, can also help identify these vulnerabilities.

What is the difference between first-order and second-order SQL injection?

First-order SQL injection occurs when user input is directly incorporated into a query, while second-order (or stored) SQL injection involves storing the user input in a database and later using it in a vulnerable query. The latter can be harder to detect initially since no immediate vulnerability is visible.

How can SQL injection vulnerabilities be prevented?

SQL injection can be prevented by using parameterized queries, which separate user input from SQL query logic. Additionally, proper whitelisting of allowed input values and avoiding dynamic SQL queries are crucial in securing applications against these attacks.

Why is it important to avoid dynamic SQL queries in applications?

Dynamic SQL queries, where user input is directly concatenated into the query, are vulnerable to SQL injection attacks. Avoiding this practice and using parameterized queries instead ensures that user input is safely treated as data, not executable code.