How bad guys hack into websites using SQL Injection
Below is a MRR and PLR article in category Internet Business -> subcategory Security.
How Cybercriminals Exploit Websites Using SQL Injection
Understanding SQL Injection Attacks
SQL Injection represents one of the most pervasive security vulnerabilities on the web today. Thousands of websites remain vulnerable to these attacks, making it crucial to understand how they work and how to protect against them.
What is SQL?
Before diving into SQL Injection, let's clarify what SQL means. SQL stands for Structured Query Language and is pronounced "sequel." It's the standard language used for accessing and manipulating data in databases. Most contemporary websites depend on databases (commonly MySQL) to store and manage their information.
A Common Scenario: The Login Form
Consider a typical login form, which website visitors encounter routinely. Users input their username and password, and the server checks these credentials. Here's a closer look at the server-side process:
The Server's Role
1. The client sends the username and password to the server.
2. The server queries the database to validate these credentials using an SQL statement, typically resembling:
```
SELECT * FROM users WHERE username='SUPPLIED_USER' AND password='SUPPLIED_PASS'
```
In SQL, single quotes (`'`) are used to delimit string variables. If a query returns any rows, the credentials are considered valid.
How SQL Injection Exploits Work
Basic Exploitation
What happens if a user sneakily inserts a single quote (`'`) into the username or password field? For instance, if the username field contains only a single quote and the password field is left blank, the query becomes:
```
SELECT * FROM users WHERE username=''' AND password=''
```
This triggers a parsing error. However, by crafting input like:
- Username: `' OR 'a'='a`
- Password: `' OR 'a'='a`
The query transforms into:
```
SELECT * FROM users WHERE username='' OR 'a'='a' AND password='' OR 'a'='a'
```
Because `'a'='a'` is always true, the query will return all rows from the `users` table, allowing unauthorized access.
Advanced Exploitation Techniques
Consider a PHP and MySQL platform as an example, with a table like:
```sql
CREATE TABLE users (
username VARCHAR(128),
password VARCHAR(128),
email VARCHAR(128)
);
```
A typical row might be:
- Username: `testuser`
- Password: `testing`
- Email: `testuser@testing.com`
The PHP code might query the database with:
```php
$query = "SELECT username, password FROM users WHERE username='".$user."' AND password='".$pass."'";
```
If the server displays MySQL error messages, attackers can use them to gather database structure information.
Exploiting Error Messages
Inputting just a `'` in the username field causes an error like:
```
You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '''' and password=''' at line 1
```
By testing with inputs like `' OR user='abc`, the resulting error (`Unknown column 'user'`) suggests non-existent columns. If there's no error with `' OR email='`, it confirms the `email` column's existence.
Knowing an email, an attacker could use:
- Username: `' OR email='testuser@testing.com`
- Password: `' OR email='testuser@testing.com`
This forms a valid query:
```
SELECT username, password FROM users WHERE username='' OR email='testuser@testing.com' AND password='' OR email='testuser@testing.com'
```
This achieves unauthorized access if such an email exists.
Conclusion
When servers expose error messages, attackers can incrementally deduce the database structure to carry out more sophisticated attacks. Protecting against SQL Injection involves implementing robust input validation and avoiding exposure of error details. By understanding how these attacks work, developers can better safeguard their systems.
You can find the original non-AI version of this article here: How bad guys hack into websites using SQL Injection.
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