Abhishek Gupta

The Sun won’t set at NIT Durgapur !

Posts Tagged ‘api’

SQL injection vulnerabilities and how to overcome

Posted by abhiitechie on April 27, 2009

SQL injection vulnerabilities and how to overcome.

According to wiki SQL injection is a code injection technique that exploits a security vulnerability occurring in the database layer of an application. The vulnerability is present when user input is either incorrectly filtered for string literal escape characters embedded in SQL statements or user input is not strongly typed and thereby unexpectedly executed. It is an instance of a more general class of vulnerabilities that can occur whenever one programming or scripting language is embedded inside another.

Let me give you an example of one of a very basic vulnerability.

Incorrectly filtered escape characters

This form of SQL injection occurs when user input is not filtered for escape characters and is then passed into a SQL statement. This results in the potential manipulation of the statements performed on the database by the end user of the application.
The following line of code illustrates this vulnerability:
statement = “SELECT * FROM users WHERE name = ‘” + userName + “‘;”
This SQL code is designed to pull up the records of the specified username from its table of users.
However, if the “userName” variable is crafted in a specific way by a malicious user, the SQL statement may do more than the code author intended. For example, setting the “userName” variable as a’ or ‘t’=’t renders this SQL statement by the parent language:

SELECT * FROM users WHERE name = ‘a’ OR ‘t’=’t’;

If this code were to be used in an authentication procedure then this example could be used to force the selection of a valid username because the evaluation of ‘t’=’t’ is always true.

While most SQL Server implementations allow multiple statements to be executed with one call, some SQL APIs such as php’s mysql_query do not allow this for security reasons.

This prevents hackers from injecting entirely separate queries, but doesn’t stop them from modifying queries.

The following value of “userName” in the statement below would cause the deletion of the “users” table as well as the selection of all data from the “data” table (in essence revealing the information of every user):

a’;DROP TABLE users; SELECT * FROM data WHERE name LIKE ‘%

This input renders the final SQL statement as follows:

SELECT * FROM users WHERE name = ‘a’;DROP TABLE users; SELECT * FROM DATA WHERE name LIKE ‘%’;

SQL injection is a nasty thing. An SQL injection is a security exploit that allows a hacker to dive into your database using a vulnerability in your code. Since many PHP programs use MySQL databases with PHP, so knowing what to avoid is handy if you want to write secure code.
Here are some SQL injection cheat sheet that has a section on vulnerabilities with PHP and MySQL. If you can avoid the practices the cheat sheet identifies, your code will be much less prone to scripting attacks.

Advertisements

Posted in mysql | Tagged: , , , , , , , , , | 2 Comments »

Database connections using JDBC – MySQL and Netbeans

Posted by abhiitechie on April 27, 2009

I am fed up of people asking me how to make Database connections in Java . No one wants to go through the painfull part of studying themselves . All they want is the short-cut . So let me dedicate this particular posts to the topic of database connections in Java .

I have MySQL 5.0 installed on my Windows. In order to make a JDBC connection to MySQL database one needs to downlad the MySQL/J connector driver from here . I will also expect that you have Netbeans 6+ installed on your machine.

Extract the zip file to a folder, you’ll see file ‘mysql-connector-java-5.0.6-bin.jar’ which is the library file that we want. Just copy the file to the library folder, for example to “C:\Program Files\Java\jdk1.6.0_02\lib” also to the “C:\Program Files\Java\jdk1.6.0_02\jre\lib directory.

Next, create a new Java project on NetBeans named ‘TestMySQL’.

Now I’m going to write some code to connect to MySQL database. I have configured MySQL service on localhost.
I’m going to use Connection and DriverMapper Classes so I need to import libraries.
import java.sql.*;

Inorder to test my connections I build my project.

So everything seems to be fine till now.

To get some data, I need to execute query on the SQL Server and get the result back to me. First, I create stmt (Statement object) and execute query in SQL language. Then I store the result on ResultSet object and iterative show the result on the output window.

Insert some data to the created table using the code

Statement stmt = null;

stmt = con.createStatement();

String SQL = “INSERT INTO ZanduBaam (Name,Roll) VALUES (‘Abhishek’,40)”;

int rowsEffected = stmt.executeUpdate(SQL);

System.out.println(rowsEffected + ” rows effected”);

Inorder to retrieve data from database , I need to execute query on the SQL Server and get the result back to me. First, I created stmt (Statement object) and execute query in SQL language. Then I store the result on ResultSet object and iterative show the result on the output window.

ResultSet rs = null; // SQL query command String SQL = “SELECT * FROM ZanduBaam”; stmt = con.createStatement(); rs = stmt.executeQuery(SQL); while (rs.next()) {
System.out.println(rs.getString(“Name”) + ” : ” + rs.getString(“Roll”));
}

Similarly you can do the required for updation and deletion .

Lots of time and sweat devoted to this post considering the fact that I have a test on Monday I should stop here.
Bbye.

Posted in Uncategorized | Tagged: , , , , , , , , , , , , , , , , , , , , , | 3 Comments »