SQL injection is a type of security exploit in which the attacker adds Structured Query Language (SQL) code to a Web form input box to gain access to resources or make changes to data. An SQL query is a request for some action to be performed on a database. Typically, on a Web form for user authentication, when a user enters their name and password into the text boxes provided for them, those values are inserted into a SELECT query. If the values entered are found as expected, the user is allowed access; if they aren't found, access is denied. However, most Web forms have no mechanisms in place to block input other than names and passwords. Unless such precautions are taken, an attacker can use the input boxes to send their own request to the database, which could allow them to download the entire database or interact with it in other destructive ways.
This technology being publicly released by some black hat will give script-kiddies the ability to pick up a freeware tool, point it at a Web site and automatically download a database without any knowledge whatsoever. I think that makes things a lot more critical and severe. The automation of SQL injection gives rise to the possibility of a SQL injection worm, which is very possible, estimates that about 60% of Web applications that use dynamic content are vulnerable to SQL injection.
According to security experts, the reason that SQL injection and many other exploits, such as cross-site scripting, are possible is that security is not sufficiently emphasized in development. To protect the integrity of Web sites and applications, it is recommended simple precautions during development such as controlling the types and numbers of characters accepted by input boxes via proper validations.
One of the simple method of injection is Authorization Bypass, which involves in bypassing the logon forms… the following example will make things clear!!
SQLQuery = "SELECT Username FROM Users WHERE Username = ‘" & strUsername & "‘ AND Password = ‘" & strPassword & "‘" strAuthCheck = GetQueryResult(SQLQuery) If strAuthCheck = "" Then boolAuthenticated = False Else boolAuthenticated = True End If
Here’s what happens when a user submits a username and password. The query will go through the Users table to see if there is a row where the username and password in the row match those supplied by the user. If such a row is found, the username is stored in the variable strAuthCheck, which indicates that the user should be authenticated. If there is no row that the user-supplied data matches, strAuthCheck will be empty and the user will not be authenticated. If strUsername and strPassword can contain any characters that you want, you can modify the actual SQL query structure so that a valid name will be returned by the query even if you do not know a valid username or a password. How? Let’s say a user fills out the logon form like this:
Login: ‘ OR ‘‘=‘ Password: ‘ OR ‘‘=‘
This will give SQLQuery the following value:
SELECT Username FROM Users WHERE Username = ‘‘ OR ‘‘=‘‘ AND Password = ‘‘ OR ‘‘=‘‘
Instead of comparing the user-supplied data with that present in the Users table, the query compares a quotation mark (nothing) to another quotation mark (nothing). This, of course, will always return true. (Please note that nothing is different from null.) Since all of the qualifying conditions in the WHERE clause are now met, the application will select the username from the first row in the table that is searched. It will pass this username to strAuthCheck, which will ensure our validation. It is also possible to use another row’s data, using single result cycling techniques.