What is a SQL Injection?
The full form of SQL is Structured Query Language. It is used to retrieve and manipulate data in the database. SQL Injection is an attack that poisons dynamic SQL statements to comment out certain parts of the statement or appending a condition that will always be true.
How SQL Injection Works
The types of attacks that may be performed victimization SQL injection vary reckoning on the sort of information engine. The attack works on dynamic SQL statements. A dynamic statement may be a statement that’s generated at run time victimization parameters word from an online kind or URI question string.
Let’s contemplate an easy internet application with a login kind. The code for the hypertext markup language kinds shown below.
- <form action=‘index.php’ method=”post”>
- <input type=”email” name=”email” required=”required”/>
- <input type=”password” name=”password”/>
- <input type=”checkbox” name=”remember_me” value=”Remember me”/>
- <input type=”submit” value=”Submit”/>
- The above form accepts the email address and password then submits them to a PHP file named index.php.
- It has the option of storing the login session in a cookie. We have deduced this from the remember_me checkbox. It uses the post method to submit data. This means the values are not displayed in the URL.
Let’s suppose the statement at the backend for checking user ID is as follows
SELECT * FROM users WHERE email = $_POST[’email’] AND password = md5($_POST[‘password’]);
- The above statement uses the values of the $_POST array directly without sanitizing them.
- The password is encrypted using the MD5 algorithm.
We will illustrate the SQL injection attack using sqlfiddle. Open the URL http://sqlfiddle.com/#!2/3286e/1 in your web browser. You will get the following window.
Note: you will have to write the SQL statements
Step 1)Enter this code in the left pane
- CREATE TABLE `techpand`.`users` (
- `id` INT NOT NULL AUTO_INCREMENT,
- `email` VARCHAR(45) NULL,
- `password` VARCHAR(45) NULL,
- PRIMARY KEY (`id`));
insert into users (email,password) values (‘[email protected]’,md5(‘abc’));
Step 2) Enter this code in the right pane
select * from users;
Step 3) Click Build Schema
Step 4)Click Run SQL. You will see the following result
Suppose a user supplies [email protected] and 1234 as the password. The statement to be executed against the database would be
SELECT * FROM users WHERE email = ‘[email protected]’ AND password = md5(‘1234′);
The above code can be exploited by commenting out the password part and appending a condition that will always be true. Let’s suppose an attacker provides the following input in the email address field.
[email protected]’ OR 1 = 1 LIMIT 1 — ‘ ]
xxx for the password.
The generated dynamic statement will be as follows.
SELECT * FROM users WHERE email = ‘[email protected]’ OR 1 = 1 LIMIT 1 — ‘ ] AND password = md5(‘1234’);
in SQL FiddleRun SQL Text box as shown below
- [email protected] ends with a single quote which completes the string quote
- OR 1 = 1 LIMIT 1 is a condition that will always be true and limits the returned results to only one record.
- ‘ AND … is a SQL comment that eliminates the password part.
Copy the above SQL statement and paste it
Hacking Activity: SQL Inject a Web Application
We have a simple web application at http://www.techpanda.org/ which is vulnerable to SQL Injection attacks for demonstration purposes only. The HTML form code above is taken from the login page. The application provides basic security such as sanitizing the email field. This means our above code cannot be used to bypass the login.
To get around that, we can instead exploit the password field. The diagram below shows the steps that you must follow
Let’s suppose an attacker provides the following input
Step 1: Enter [email protected] as the email address
Step 2: Enter xxx’) OR 1 = 1 — ]
Click on Submit button
You will be directed to the dashboard
The generated SQL statement will be as follows
SELECT * FROM users WHERE email = ‘[email protected]’ AND password = md5(‘xxx’) OR 1 = 1 — ]’);
The diagram below illustrates the statement has been generated.
The statement intelligently assumes md5 encryption is used
Completes the single quote and closing bracket
Appends a condition to the statement that will always be true
In general, a successful SQL Injection attack attempts several different techniques such as the ones demonstrated above to carry out a successful attack.
Other SQL Injection attack types
SQL Injection can do more harm than just bypassing login algorithms. Some of the attacks include
Executing commands on the server that can download and install malicious programs such as Trojans
Exporting valuable data such as credit card details, email, and passwords to the attacker’s remote server
Getting user login details etc
The above list is not exhaustive; it just gives you an idea of what SQL Injection
Automation Tools for SQL Injection
In the above example, we used manual attack techniques based on our vast knowledge of SQL. There are automated tools that can help you perform the attacks more efficiently and within the shortest possible time. These tools include
SQLDict – http://ntsecurity.nu/toolbox/sqldict/
SQLSmack – http://www.securiteam.com/tools/5GP081P75C.html
SQLPing 2 – http://www.sqlsecurity.com/downloads/sqlping2.zip?attredirects=0&d=1
SQLMap – http://sqlmap.org/
How to guard against SQL Injection Attacks
An organization can adopt the following policy to protect itself against SQL Injection attacks.
User input should never be trusted. It must always be sanitized before it is used in dynamic SQL statements.
Stored procedures – these can encapsulate the SQL statements and treat all input as parameters.
Prepared statements –prepared statements to work by creating the SQL statement first then treating all submitted user data as parameters. This does not affect the syntax of the SQL statement.
Regular expressions –these can be used to detect potential harmful code and remove it before executing the SQL statements.
Database connection user access rights –only necessary access rights should be given to accounts used to connect to the database. This can help reduce what the SQL statements can perform on the server.
Error messages –these should not reveal sensitive information and where exactly an error occurred. Simple custom error messages such as “Sorry, we are experiencing technical errors. The technical team has been contacted. Please try again later” can be used instead of display the SQL statements that caused the error.
Hacking Activity: Use Havij for SQL Injection
In this practical scenario, we are going to use the Havij Advanced SQL Injection program to scan a website for vulnerabilities.
Note: your anti-virus program may flag it due to its nature. You should add it to the exclusions list or pause your anti-virus software.
The image below shows the main window for Havij
The above tool can be used to assess the vulnerability of a web site/application.