Justin Clarke is a co-founder and Director at Gotham Digital Science. He has over twelve years of experience in assessing the security of networks, web applications, and wireless networks. He is the author of the open source SQLBrute blind SQL injection testing tool, several books, and is the Chapter Leader for the London chapter of OWASP. In this interview he discusses SQL injection and his latest book.

Exactly how big of a problem is SQL injection? Can you provide a rough picture to our readers not familiar with the issue?

SQL injection is a huge problem. It is both fairly common, as well as having the potential to be a huge risk to a business either directly or indirectly. A good example of the risk of SQL Injection is the recent revelation that SQL injection was a key part in a number of the recent large credit card data breaches - Heartland, Hannaford, TJX and others. In these cases, SQL injection was used in order to get further into an organization and do something else, however in a lot of cases SQL injection can be serious enough all on its own. I've seen examples such as a small US bank that had over 5,000 mortgage applications stolen from an application via SQL Injection, and hence all of the information needed to steal all of those people's identities.

For those not familiar with SQL injection, it occurs when unvalidated user input is included within Structured Query Language (SQL) statements that are dynamically assembled within the application. For example, say the application is assembling a query for product information with a “productid” variable supplied by the user with a query something like this:

string query = "SELECT * from products WHERE productid =" + productid


Where the “productid” variable is as the developer expects, this works fine. However if the “productid” variable contains SQL language statements instead of the expected values, an attacker can modify what the query does, and even execute totally different database functionality in some cases. For example, on Microsoft SQL Server the attacker may be able to execute operating system commands like the following:

Attacker supplies the following value for “productid” -> 1; exec xp_cmdshell('cmd.exe /c ping 10.11.12.13')--

What's are the main motivations behind SQL injection attacks? Precisely what are the attackers after?

The main motivation is usually to access the data in the application or applications that are present on the database server supporting the application. This could take the form of obtaining access to data in the application (for example, getting people's usernames and password), or modifying or deleting information in the database (for example, inserting a link to a malicious JavaScript file into the application's front page).