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SQL Injection - Primer

SQL Injection is a security vulnerability where a web application allows a user to send un-sanitized input into a SQL query.

The textbook example is that a web application has a username field that inserts the user's input into the following SQL query:

statement = "SELECT * FROM users WHERE name = '" + userName + "';"

The user then types a' or '1'='1 into the username field. This creates the following SQL statement:

SELECT * FROM users WHERE name = 'a' or '1'='1'

If the statement variable is used for the authentication procedure then the evaluation of the SQL statement will always be true.

An attacker can cause damage if they appended something like, '; DROP TABLE users;--

This would produce the following statement:

statement = "SELECT * FROM users WHERE name = ''; DROP TABLE users;--';

Which would result in the users table being deleted from the Database.