How does the LIMIT clause in SQL queries lead to injection attacks

Question

I've been learning about SQL injection attacks and recently came across an example where the LIMIT clause was exploited in an injection attack. Most of the material I’ve read focuses on SQL injections that occur in SELECT, INSERT, and UPDATE queries, but I didn’t realize that LIMIT could be vulnerable too.

How exactly does the LIMIT clause introduce a risk of SQL injection? Does it depend on how the data is passed into the query, or can it happen even with properly sanitized inputs? I would appreciate some examples or insights to better understand how this works and how to prevent it.

Answer 1

The LIMIT clause in SQL can indeed be a vector for SQL Injection Attacks.

SQL Injection occurs when attackers manipulate queries by injecting malicious input, which allows them to gain unauthorized access to the data.

Let's consider a query that uses the LIMIT clause:

SELECT * FROM users WHERE username = 'admin' LIMIT 1;

If the input is not properly sanitized, an attacker can use something like:

admin' OR '1'='1' LIMIT 1; --

Eventually the query will become:

SELECT * FROM users WHERE username = 'admin' OR '1'='1' LIMIT 1; --

Now, this query would return the first user from the users table which will potentially bypass all the authentication checks.

In order to prevent this kind of vulnerability:

• Use Prepared Statements that help in separating SQL code from data. It ensures that the user input does not alter the query structure.
• Validate Input which always validates and sanitizes input to meet expected formats.

Comments

Interesting! But I’m a bit confused—how does the LIMIT clause specifically come into play here? Wouldn’t the injection work just the same without LIMIT in the query?