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SQL Injection: What is it?

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PostPosted: Thu Nov 15, 2007 5:27 pm    Post subject: SQL Injection: What is it? Reply with quote

SQL Injection is one of the many web attack mechanisms used by hackers to steal data from organizations. It is perhaps one of the most common application layer attack techniques used today. It is the type of attack that takes advantage of improper coding of your web applications that allows hacker to inject SQL commands into say a login form to allow them to gain access to the data held within your database.

In essence, SQL Injection arises because the fields available for user input allow SQL statements to pass through and query the database directly.

SQL Injection: An In-depth Explanation
Web applications allow legitimate website visitors to submit and retrieve data to/from a database over the Internet using their preferred web browser. Databases are central to modern websites – they store data needed for websites to deliver specific content to visitors and render information to customers, suppliers, employees and a host of stakeholders. User credentials, financial and payment information, company statistics may all be resident within a database and accessed by legitimate users through off-the-shelf and custom web applications. Web applications and databases allow you to regularly run your business.

SQL Injection is the hacking technique which attempts to pass SQL commands (statements) through a web application for execution by the backend database. If not sanitized properly, web applications may result in SQL Injection attacks that allow hackers to view information from the database and/or even wipe it out.

Such features as login pages, support and product request forms, feedback forms, search pages, shopping carts and the general delivery of dynamic content, shape modern websites and provide businesses with the means necessary to communicate with prospects and customers. These website features are all examples of web applications which may be either purchased off-the-shelf or developed as bespoke programs.

These website features are all susceptible to SQL Injection attacks which arise because the fields available for user input allow SQL statements to pass through and query the database directly.

SQL Injection: A Simple Example
Take a simple login page where a legitimate user would enter his username and password combination to enter a secure area to view his personal details or upload his comments in a forum.

When the legitimate user submits his details, an SQL query is generated from these details and submitted to the database for verification. If valid, the user is allowed access. In other words, the web application that controls the login page will communicate with the database through a series of planned commands so as to verify the username and password combination. On verification, the legitimate user is granted appropriate access.

Through SQL Injection, the hacker may input specifically crafted SQL commands with the intent of bypassing the login form barrier and seeing what lies behind it. This is only possible if the inputs are not properly sanitised (i.e., made invulnerable) and sent directly with the SQL query to the database. SQL Injection vulnerabilities provide the means for a hacker to communicate directly to the database.

The technologies vulnerable to this attack are dynamic script languages including ASP, ASP.NET, PHP, JSP, and CGI. All an attacker needs to perform an SQL Injection hacking attack is a web browser, knowledge of SQL queries and creative guess work to important table and field names. The sheer simplicity of SQL Injection has fuelled its popularity.

Other contents:
Why is it possible to pass SQL Queries to the database even though this is hidden behind a firewall?
Is my database at risk to SQL Injection?
What is the impact of SQL Injection?
Example of a SQL Injection Attack
How do I prevent SQL Injection attacks?

Why is it possible to pass SQL queries directly to a database that is hidden behind a firewall and any other security mechanism?
Firewalls and similar intrusion detection mechanisms provide little or no defense against full-scale SQL Injection web attacks.

Since your website needs to be public, security mechanisms will allow public web traffic to communicate with your web application/s (generally over port 80/443). The web application has open access to the database in order to return (update) the requested (changed) information.

In SQL Injection, the hacker uses SQL queries and creativity to get to the database of sensitive corporate data through the web application.

SQL or Structured Query Language is the computer language that allows you to store, manipulate, and retrieve data stored in a relational database (or a collection of tables which organise and structure data). SQL is, in fact, the only way that a web application (and users) can interact with the database. Examples of relational databases include Oracle, Microsoft Access, MS SQL Server, MySQL, and Filemaker Pro, all of which use SQL as their basic building blocks.

SQL commands include SELECT, INSERT, DELETE and DROP TABLE. DROP TABLE is as ominous as it sounds and in fact will eliminate the table with a particular name.

In the legitimate scenario of the login page example above, the SQL commands planned for the web application may look like the following:

SELECT count(*)
FROM users_list_table

In plain English, this SQL command (from the web application) instructs the database to match the username and password input by the legitimate user to the combination it has already stored.

Each type of web application is hard coded with specific SQL queries that it will execute when performing its legitimate functions and communicating with the database. If any input field of the web application is not properly sanitised, a hacker may inject additional SQL commands that broaden the range of SQL commands the web application will execute, thus going beyond the original intended design and function.

A hacker will thus have a clear channel of communication (or, in layman terms, a tunnel) to the database irrespective of all the intrusion detection systems and network security equipment installed before the physical database server.

Is my database at risk to SQL Injection?
SQL Injection is one of the most common application layer attacks currently being used on the Internet. Despite the fact that it is relatively easy to protect against SQL Injection, there are a large number of web applications that remain vulnerable.

Mod-Note: removed link spamming own website. Please review the rules for posting.~g
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