What is SQL Injection and How to Prevent It?

PCI DSS Requirement 6.5.1 requires that your organization’s applications are not affected by injection flaws, especially SQL injection. Malicious people commonly use injection defects to compromise applications.

SQL Injection is an attack method used to attack applications that are driven by databases. The attacker adds new SQL statements to the relevant field on the standard application screen, using SQL language features.

See Also: What is Cross-Site Scripting (XSS) and How to Prevent It?

SQL Injection exploits a vulnerability in the software of the applications. For example, SQL statements are embedded in the part where the application expects user login information; if the incoming data’s content is not filtered within the application or is incorrectly filtered, the application appears to run without any error with the code embedded in it.

Although SQL Injection is known as a type of attack mostly used for websites, it can occur in all applications based on SQL databases.

SQL Injection attack can be defined as injecting SQL commands into SQL queries of web applications. A successful SQL injection attack allows a malicious programmer to access a web application database and manage it.

See Also: PCI DSS Requirement 6 Explained

SQL injection attacks allow the attackers to log in with the information of one of the users in the system, interfere with existing data, cancel or change some operations, reveal all data in the database, destroy all data in the database, and become a system administrator on the database server.

See Also: What is OS Command Injection and How to Prevent It?

SQL injection is a type of Injections vulnerability that ranks 1st in the OWASP Top 10 ranking. SQL injection is to insert SQL queries into the input field received from the user, which will manipulate the SQL query running at the back and provide outputs that will serve our purpose.

What are the Types of SQLi (SQL Injection)?

SQL is a query language used to manage databases. With SQL, operations are performed on the database, and data management is provided efficiently. It does these with various syntaxes within itself. These syntaxes and commands make up the SQL language.

There are many different variants of the SQL language. The most common examples are Microsoft SQL Server, Oracle, Mysql, Postgresql products. Although these different types of SQL are very similar in terms of SQL syntax and meaning, it can be said that some rules are quite different from each other. These widely used database management systems are used in various platforms by the purpose.

Also known as SQLi, SQL Injection is a common method of attack that uses malicious SQL code to exploit databases to access information that we can not see. This information can include any number of items, including sensitive company data, user lists, or specific customer details.

SQL Injection has an enormous impact on an enterprise. A effective attack can result in unauthorized viewing of user lists, removing all tables, and in some instances, acquiring administrative rights over a database by an intruder, all of which are extremely damaging to an organization.

When estimating the potential expense of an SQLi, it is important to note that consumer confidence would be lost if personal information such as phone numbers, addresses, and credit card information is compromised.

SQL Injection can be used in many ways to cause serious problems. Using SQL Injection, an attacker can bypass authentication in a database, access data, modify, and delete data.

In some cases, SQL Injection may also be used to execute commands on the operating system, potentially enabling an attacker to escalate to more malicious attacks within a network situated behind a firewall.

SQL Injection can be divided into three main categories:

  • In-band SQL Injection (Classic)
    • Error-based SQL Injection
    • Union-based SQL Injection
  • Inferential SQL Injection (Blind)
    • Boolean-based SQL Injection
    • Time-based SQL Injection
  • Out-of-band SQL Injection

1. In-band SQL (Classic)

It is the most common and easy to use of SQL Injection attacks. An attacker uses the same communication channel to both initiate the attack and collects the results.

1 a. Error-based SQL Injection

It is a SQL Injection technique based on error messages sent by the database server to learn about the database structure. In certain instances, error-based SQL injection alone is sufficient for the entire database to be enumerated by an attacker. While bugs can be beneficial in developing a web application, they should be disabled on a live site or logged into a limited-access file instead.

The application is forced into error, and if the error message is caught, the presence of SQL injection vulnerability is detected.

Select * from stores where product_id = blah 'or 1 = 1 - (the system will ignore everything after here)

Select * from users where username = 'blah' or 'a' = 'a' - and password = 'pass'

1b. Union-based SQL Injection

It is a SQL injection technique that combines the results of two or more “SELECT” statements into a single result using the UNION SQL operator and then returns them as part of the HTTP response. This HTTP response may contain data that could be used by the attacker.

Select * from stores where product_id=1 union select 1, database(), user(),4#

Select * from stores where id = 1 '

2.Inferential SQL (Blind) Injection

Inferential SQL injection will take longer for an attacker to hack, unlike in-band SQL injection, but it is just as risky as other forms of SQL injection. In the inferential SQLi attack, no data is transmitted through the web application, and the attacker cannot see the result of the attack. For this reason, such attacks are often referred to as “blind SQL Injection attacks.”

Information about a table or column or technical details on the database cannot be accessed directly from the database. Still, if the requested information is tried letter by letter, correct results will be obtained.

For this reason, it is difficult to do it manually, and if this gap is detected, the opening is abused with automated programs. Instead, an attacker can rebuild the database structure by sending data, observing the web application’s response, and the database server’s resulting behavior.

2 a. Boolean-based Blind SQL Injections

This is a SQL injection technique based on submitting a database SQL query and forces the server to return a different answer depending on whether TRUE or FALSE is returned by the query.

Returns True – False based on the result of the logical expression sent in Boolean SQL injection.

The content inside the HTTP response will adjust or stay the same depending on the outcome. This helps an intruder to be able to know whether, even if the database does not return any data, the payload returns true or false. This attack is usually slow, as an attacker will need to enumerate a database character by character.

www.website.local/item.php? id = 34 and 1 = 2

2b. Time-based Blind SQL Injections

The attacker sends an SQL query to the database, causing the database to wait (a time in seconds) for a response. The attacker can see the time it takes for the database to respond, whether a query is correct or incorrect.

In Time-Based SQL Injection, since it cannot be determined whether the sent query is executed or not, functions such as sleep () are placed into the query to see if the system response is delayed.

An HTTP response will be produced immediately or after a waiting period, depending on the outcome. The attacker can calculate whether the message they use returned true or false without relying on the data in the database.

http://www.website.local/item.php? id = 34 and if (1 = 1, sleep (10), false)

3.Out-of-band SQL Injection

This technique is not very common because it mostly depends on some features enabled on the web application’s database server. This attack occurs when the attacker cannot use the same channel to initiate the attack and collect the results.

Out-of-band techniques offer an alternative to inferential time-based techniques to an attacker, especially when server responses are not stable. Out-of-band SQLi techniques rely on the database server’s ability to make DNS or HTTP requests to provide data to an attacker.

How Dangerous is SQL injection?

It is essential to understand what SQL Injection vulnerabilities can cause when used successfully. It should be noted that according to the DBMS (MySQL, SQL Server, Oracle, etc.) the web application uses, the attacker can take a series of actions that go far beyond merely manipulating the database.

An attacker can read the file system, execute OS commands, install Shell, access the remote network, and have the entire infrastructure with a SQL Injection attack. Of all the vulnerabilities that can affect web applications, SQL injections are the first to be checked by hackers due to the fastest results.

How to Prevent SQL Injection Attacks?

It is estimated that most of today’s web sites are not secure due to the SQL language’s vulnerabilities. In addition to preventing SQLI attacks from happening, there are several effective ways to protect against them.

The first step is to check user input. If the user enters any SQL statement, this entry should be checked and evaluated by the system.

Another solution is to commonly use a web application firewall (WAF) to filter out SQL Injection or other online threats. Modern web application firewalls are also often integrated with other security solutions.

To wrap it up in general, to prevent SQL Injection attacks, you need to follow the steps below:

  • Don’t use dynamic SQL
  • Check user-provided input
  • Do not store sensitive data in plain text.
  • Limit database permissions and privileges
  • Avoid showing database errors directly to the user.
  • For web applications that access databases
  • Use a web application firewall (WAF).
  • Using a security testing solution for a web application to monitor web applications that regularly communicate with databases.
  • Keep databases up to date.

What Are The Defense Methods Against SQL Injection Attacks?

Attackers can use SQL queries that the application wants to execute from the database; It provides by manipulating the “SQL engine,” that is, the SQL engine with specially prepared SQL statements.

For example, it uses SQL statements that trick the database engine into logging into an application without a username and password. It can change unauthorized data, create fake records, add users or upgrade users to higher access levels. Can access data without permission.

There are easy ways to avoid SQL injection vulnerability in applications:

  • Discover SQL injection vulnerabilities by routinely testing your applications using both static and dynamic testing.
  • You can protect SQL injection vulnerabilities by using parameterized queries.
  • Process the input value received from the user by software checking.
  • Ensure that each application has its database credentials and that these credentials have the minimum rights the application needs.

When developing applications, you must ensure that they are free from any injection defects, especially SQL injection vulnerabilities. The most basic solution is to verify the data coming to the application.

You have some parameterized query, or make sure that the array of data coming into the application is examined before execution. When you have a parameterized query, you will not receive the data stream provided by end-users, and you will not develop your query accordingly.

When developing software, your team should make sure they are not affected by SQL injection. Be sure to write test scripts for SQL injection as part of your secure code development process.

To verify compliance with PCI DSS Requirement 6.5.1 and protection from injection errors, an assessor will review your policies and procedures regarding application development and interview responsible personnel.

There are many useful articles on Owasp’s website, such as weaknesses in web applications, how vulnerabilities occur, how to exploit and prevent these vulnerabilities. You can get more detailed information about SQL Injection from the links below.

OWASP: SQL Injection

OWASP SQL Injection Prevention Cheat Sheet

OWASP TOP 10: A1:2017-Injection

Surkay Baykara
Surkay Baykarahttps://www.pcidssguide.com
A passionate Senior Information Security Consultant working at Cyberwise. Over the past 15+ years my professional career has included several positions beginning as a developer and IT administrator, working my way up to a senior Technical Performance Consultant before joining Biznet back in 2015. I had several different roles at Cyberwise, including Penetration Tester and PCI DSS QSA. In my job as a QSA, I found my passion and worked closely with the Audit and Compliance team. I've been working inside InfoSec for over 15 years, coming from a highly technical background. I have earned several certifications during my professional career including; CEH, CISA, CISSP, and PCI QSA.

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