This article explains how to test whether a website is safe from SQL injection using the SQLMAP penetration testing tool.
What is SQL Injection?
SQL Injection is a code injection technique where an attacker executes malicious SQL queries that control a web application’s database. With the right set of queries, a user can gain access to information stored in databases. SQLMAP tests whether a ‘GET’ parameter is vulnerable to SQL Injection.
For example, Consider the following php code segment:
$variable = $_POST['input'];
mysql_query("INSERT INTO `table` (`column`) VALUES ('$variable')");
If the user enters “value’); DROP TABLE table;–” as the input, the query becomes
INSERT INTO `table` (`column`) VALUES('value'); DROP TABLE table;--')
which is undesirable for us, as here the user input is directly compiled along with the pre-written sql query. Hence the user will be able to enter an sql query required to manipulate the database.
Where can you use SQLMAP?
If you observe a web url that is of the form http://testphp.vulnweb.com/listproducts.php?cat=1, where the ‘GET’ parameter is in bold, then the website may be vulnerable to this mode of SQL injection, and an attacker may be able to gain access to information in the database. Furthermore, SQLMAP works when it is php based.
A simple test to check whether your website is vulnerable would be to replace the value in the get request parameter with an asterisk (*). For example,
http://testphp.vulnweb.com/listproducts.php?cat=*
If this results in an error such as the error given above, then we can conclusively say that the website is vulnerable.
Installing sqlmap
SQLMAP comes pre-installed with kali Linux, which is the preferred choice of most penetration testers. However, you can install sqlmap on other debian based linux systems using the command
sudo apt-get install sqlmap
Usage
In this article, we will make use of a website that is designed with vulnerabilities for demonstration purposes:
http://testphp.vulnweb.com/listproducts.php?cat=1
As you can see, there is a GET request parameter (cat = 1) that can be changed by the user by modifying the value of cat. So this website might be vulnerable to SQL injection of this kind.
To test for this, we use SQLMAP. To look at the set of parameters that can be passed, type in the terminal,
sqlmap -h
The parameters that we will use for the basic SQL Injection are shown in the above picture. Along with these, we will also use the –dbs and -u parameter, the usage of which has been explained in Step 1.
Using SQLMAP to test a website for SQL Injection vulnerability:
- Step 1: List information about the existing databases
So firstly, we have to enter the web url that we want to check along with the -u parameter. We may also use the –tor parameter if we wish to test the website using proxies. Now typically, we would want to test whether it is possible to gain access to a database. So we use the –dbs option to do so. –dbs lists all the available databases.
sqlmap -u http://testphp.vulnweb.com/listproducts.php?cat=1 --dbs
- We get the following output showing us that there are two available databases. Sometimes, the application will tell you that it has identified the database and ask whether you want to test other database types. You can go ahead and type ‘Y’. Further, it may ask whether you want to test other parameters for vulnerabilities, type ‘Y’ over here as we want to thoroughly test the web application.
- We observe that there are two databases, accurate and information_schema
- Step 2: List information about Tables present in a particular Database
To try and access any of the databases, we have to slightly modify our command. We now use -D to specify the name of the database that we wish to access, and once we have access to the database, we would want to see whether we can access the tables. For this, we use the –tables query. Let us access the accurate database.
sqlmap -u http://testphp.vulnweb.com/listproducts.php?cat=1 -D acuart --tables
Tables
- In the above picture, we see that 8 tables have been retrieved. So now we definitely know that the website is vulnerable.
- Step 3: List information about the columns of a particular table
If we want to view the columns of a particular table, we can use the following command, in which we use -T to specify the table name, and –columns to query the column names. We will try to access the table ‘artists’.
sqlmap -u http://testphp.vulnweb.com/listproducts.php?cat=1 -D acuart -T artists --columns
Columns
- Step 4: Dump the data from the columns
Similarly, we can access the information in a specific column by using the following command, where -C can be used to specify multiple column name separated by a comma, and the –dump query retrieves the data
sqlmap -u http://testphp.vulnweb.com/listproducts.php?cat=1 -D acuart -T artists -C aname --dump
- From the above picture, we can see that we have accessed the data from the database. Similarly, in such vulnerable websites, we can literally explore through the databases to extract information
Prevent SQL Injection
SQL injection can be generally prevented by using Prepared Statements . When we use a prepared statement, we are basically using a template for the code and analyzing the code and user input separately. It does not mix the user entered query and the code. In the example given at the beginning of this article, the input entered by the user is directly inserted into the code and they are compiled together, and hence we are able to execute malicious code. For prepared statements, we basically send the sql query with a placeholder for the user input and then send the actual user input as a separate command.
Consider the following php code segment.
$db = new PDO('connection details');
$stmt = db->prepare("Select name from users where id = :id");
$stmt->execute(array(':id', $data));
In this code, the user input is not combined with the prepared statement. They are compiled separately. So even if malicious code is entered as user input, the program will simply treat the malicious part of the code as a string and not a command.
Note: This application is to be used solely for testing purposes
Related Article
Basic SQL injection and mitigation
Reference:stackoverflow.com
