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SQL Injection

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Databases are fundamental components of Web applications. Databases enable Web applications to store data, preferences and content elements. Using SQL, Web applications interact with databases to dynamically build customized data views for each user. A common example is a Web application that manages products. In one of the Web application's dynamic pages (such as ASP), users are able to enter a product identifier and view the product name and description. The request sent to the database to retrieve the product's name and description is implemented by the following SQL statement.
                      

SELECT ProductName, ProductDescription 
FROM Products 
WHERE ProductNumber = ProductNumber
 
Typically, Web applications use string queries, where the string contains both the query itself and its parameters. The string is built using server-side script languages such as ASP, JSP and CGI, and is then sent to the database server as a single SQL statement. The following example demonstrates an ASP code that generates a SQL query.
 
sql_query= "
SELECT ProductName, ProductDescription 
FROM Products 
WHERE ProductNumber = " & Request.QueryString("ProductID")
 
The call Request.QueryString("ProductID") extracts the value of the Web form variable ProductID so that it can be appended as the SELECT condition.
 
When a user enters the following URL:
 
http://www.mydomain.com/products/products.asp?productid=123
 
The corresponding SQL query is executed:
 
SELECT ProductName, ProductDescription 
FROM Products 
WHERE ProductNumber = 123
 
An attacker may abuse the fact that the ProductID parameter is passed to the database without sufficient validation. The attacker can manipulate the parameter's value to build malicious SQL statements. For example, setting the value "123 OR 1=1" to the ProductID variable results in the following URL:
 
http://www.mydomain.com/products/products.asp?productid=123 or 1=1
 
The corresponding SQL Statement is:
 
SELECT ProductName, Product Description
FROM Products
WHERE ProductNumber = 123 OR 1=1
 
This condition would always be true and all ProductName and ProductDescription pairs are returned. The attacker can manipulate the application even further by inserting malicious commands. For example, an attacker can request the following URL:
 
http://www.mydomain.com/products/products.asp?productid=123; DROP 
TABLE Products
 
In this example the semicolon is used to pass the database server multiple statements in a single execution. The second statement is "DROP TABLE Products" which causes SQL Server to delete the entire Products table.
 
An attacker may use SQL injection to retrieve data from other tables as well. This can be done using the SQL UNION SELECT statement. The UNION SELECT statement allows the chaining of two separate SQL SELECT queries that have nothing in common. For example, consider the following SQL query:
 
SELECT ProductName, ProductDescription 
FROM Products 
WHERE ProductID = '123' UNION SELECT Username, Password FROM Users;
 
The result of this query is a table with two columns, containing the results of the first and second queries, respectively. An attacker may use this type of SQL injection by requesting the following URL:
 
http://www.mydomain.com/products/products.asp?productid=123 UNION 
SELECT user-name, password FROM USERS

" (end of quote)

Alternate scripts for SQL injection is also known as...
***       **
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statement = "SELECT * FROM users WHERE name = '" + userName + "';"
 
' or '1'='1
 
' or '1'='1' -- '
' or '1'='1' ({ '
' or '1'='1' /* '
 
SELECT * FROM users WHERE name = '' OR '1'='1';
 
SELECT * FROM users WHERE name = '' OR '1'='1' -- ';

To prevent this.. from happening SQL Database maintenance is important... Always patch your Database to highest patch level. To minimize the risk of getting attack.

Microsoft also release a list of patches for SQL Database Injection. You may refer the below information.

*http://technet.microsoft.com/en-us/security/bulletin/ms02-038
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