SQL Injection Tutorial: Learn About Injection Attacks, Vulnerabilities and How to Prevent SQL Injections

What is SQL Injection

SQL Injection is a type of web application security vulnerability in which an attacker is able to submit a database SQL command which is executed by a web application, exposing the back-end database. A SQL Injection attack can occur when a web application utilizes user-supplied data without proper validation or encoding as part of a command or query. The specially crafted user data tricks the application into executing unintended commands or changing data. SQL Injection allows an attacker to create, read, update, alter, or delete data stored in the back-end database. In its most common form, a SQL Injection attack gives access to sensitive information such as social security numbers, credit card number or other financial data. According to Veracode’s State of Software Security Report SQL Injection is one of the most prevalent types of web application security vulnerability.

Key Concepts of a SQL Injection Attack

• SQL injection is a software vulnerability that occurs when data entered by users is sent to the SQL interpreter as a part of an SQL query
• Attackers provide specially crafted input data to the SQL interpreter and trick the interpreter to execute unintended commands
• Attackers utilize this vulnerability by providing specially crafted input data to the SQL interpreter in such a manner that the interpreter is not able to distinguish between the intended commands and the attacker’s specially crafted data. The interpreter is tricked into executing unintended commands
• a SQL Injection attack exploits security vulnerabilities at the database layer. By exploiting the SQL injection flaw, attackers can create, read, modify, or delete sensitive data

SQL Injections: The Most Prevalent Type of Application Security Vulnerability

With over 20% of all web vulnerabilities being attributed to SQL Injection, this is the 2nd most common software vulnerability and having the ability to find and prevent SQL injection should be top of mind for web developers and security personnel. In general, a SQL Injection attack exploits a web application which does not properly validate or encode user-supplied input and then uses that input as part of a query or command against a back-end database. For example, a typical form may ask for a ID and create a URL: http://www.somewebsite.com/id/id.asp?id=somedata. An attacker using SQL Injection may enter "somedata or 1=1". If the web application does not properly validate or encode the user-supplied data and sends it directly to the database, the reply to the query will expose all ids in the database since the condition "1=1" is always true. This is a basic example, but it illustrates the importance of sanitizing user-supplied data before using it in a query or command.

Preventing SQL Injection

• SQL injection can be prevented if you adopt an input validation technique in which user input is authenticated against a set of defined rules for length, type, and syntax and also against business rules.
• You should ensure that users with the permission to access the database have the least privileges. Additionally, do not use system administrator accounts like “sa” for Web applications. Also, you should always make sure that a database user is created only for a specific application and this user is not able to access other applications. Another method for preventing SQL injection attacks is to remove all stored procedures that are not in use.
• Use strongly typed parameterized query APIs with placeholder substitution markers, even when calling stored procedures
• Show care when using stored procedures since they are generally safe from injection. However, be careful as they can be injectable (such as via the use of exec() or concatenating arguments within the stored procedure).