What is Blind SQL Injection?
Let’s talk first about plain, old-fashioned, no-frills SQL injection. This is a hacking method that allows an unauthorized attacker to access a database server. It is facilitated by a common coding blunder: the program accepts data from a client and executes SQL queries without first validating the client’s input. The attacker is then free to extract, modify, add, or delete content from the database. In some circumstances, he may even penetrate past the database server and into the underlying operating system.1
Hackers typically test for SQL injection vulnerabilities by sending the application input that would cause the server to generate an invalid SQL query. If the server then returns an error message to the client, the attacker will attempt to reverse-engineer portions of the original SQL query using information gained from these error messages. The typical administrative safeguard is simply to prohibit the display of database server error messages. Regrettably, that’s not sufficient.
If your application does not return error messages, it may still be susceptible to “blind” SQL injection7 attacks.