In this article, we are going to learn about SQL Injection. We are going to define SQL Injection, look at its common uses, look at a few examples, and its consequences. This article serves as an introduction to SQL injection.

SQL Injection, also known as SQLi, is one of the most common web hacking techniques that hackers use to input malicious SQL statements that may destroy a database or gain them unqualified access/data to the system.

SQL Injection is a common vector attack that may have unlimited gross effects to any organization which includes breach of authentication, integrity, and confidentiality in business concerns. This may result in loss of customer trust and the effects are not favorable in any business environment.

SQL attacks SQL databases and web applications or web sites, which require user input, are the biggest targets.
The history of SQL Injection dates back to the late 90s, and since then it remains a major security concern, even in huge organizations.

SQL Injection allows attackers to override application security parameters and allow them access to confidential information or in some cases delete or tamper with sensitive data to their advantage. According to this, the attack report of 2012 reveals that an average web application receives four attacks per month and in most cases, financial institutions suffer twice as much as other industries.

SQL Queries
Before we get in-depth with SQL Injection, it is best that we understand what SQL is. SQL is an abbreviation for Structured Query Language and is used to communicate with relational databases. SQL has its set of commands and syntax and this is used to manipulate data from a database. SQL commands are used to retrieve, insert, update, or delete data in a database. A simple SQL command is the 'SELECT' statement, which is used to retrieve data from one or more tables. E.g.

This statement will simply retrieve a list of all customers from a table. Likewise, an SQL query may also be used to update or delete data within a table. E.g.

This statement updates the customer with customer number ‘XY99’ to ‘xxxxx’. And likewise,
Will delete all the data in the customers table.

Using such knowledge of SQL we can now explore the effects and uses of SQL Injection in the real world.
Types of SQL Injection
In-band SQLi (Classic)
Inferential SQLi (Blind)
Out-of-band SQLi

SQL Injection in web pages (examples)
SQL injection may occur when a user is required to input some data using given interface controls such as username or a password and the malicious user knowingly inputs an SQL statement such as ‘or 1=1’ in the password field.

Such a query may return a result set as shown below.
This statement may end up giving the malicious user all the user names and passwords in that particular table hence giving him/her access to the application and a lot of damage may result using one malicious SQL statement.

In some cases, it may be because of incorrectly filtered escape characters that the application may end up running malicious queries that may even DROP/UPDATE / ALTER database contents. Such as shown in the example below:

int user_id=getAuthUserid(); 
String query =” Select * from tbl_users where user_id = '" + user_id + "'; 
” 

The above code intends to get a user’s ID and use it to authenticate the user but if the malicious user then knowingly crafts the user_id variable using any one of the SQL comments(/*,--,{) like as follows to block the rest of the query,
' OR '1'='1'; -- 
' OR '1'='1'; /* 
' OR '1'='1'; { 

Then the query may be executed as:
Select * from tbl_users where user_id='' OR '1'='1'; 

This query will give the malicious user access to all of the table columns and this may result in serious consequences.

Another example includes the use of harmful SQL statement, which drops a table from the database through user input,
It is common practice for many developers to use batch executions and in this case, the attacker may end up deleting all the important data in a given table. In most cases perpetrators of Injection are people with a little bit of expertise in programming and their intentions and knowledge of the application will determine how dangerous they can be once they hack into any system. Apart from Drop/Delete statements, hackers may use select or update SQL statements to obtain or manipulate data in an unfavorable way to cause harm to the application.

The expected result set may be as follows:
As shown in most of the examples above, hackers maybe people with actual intent to cause harm or gain malicious access and they target loose ends such as poor SQL commands on authentication and it is important that prevention measures are taken to avoid SQL Injection.

Results of SQL Injection
Authentication
If the SQL statements used not secure this may lead to hackers getting access to the entire system and damaging the system.

Confidentiality
Since a database always carries sensitive data the advent of a malicious intruder will damage the organization’s reputation.

Authorization
If authorization data is contained within the database they may allow the malicious user to change information and result in the company’s disrepute.

Integrity
Just as it may be possible to read sensitive information, it is also possible to make changes or even delete this information with a SQL Injection attack.

Can SQL Injection be prevented or managed? Yes. We discuss this in my next article SQL Injection Protection Methods and in upcoming articles we also look at an ASP.net example of SQL Injection, Other Injection flaws, Blind, and time-based SQL Injection, and many more.