What is SQL injection attack?

SQL injection attack is a security threat that can be as deadly as it is clever. An attacker can exploit the data input mechanisms in an application to manipulate the generated SQL query to his advantage. This can lead to catastrophic events.

SQL injection attacks are often considered obsolete by many people. They are, however, a reality. SQL injections were responsible for a majority of security exploits against Rails apps. This shows that even a robust framework like Ruby on Rails, which counts as an established ORM in Active Record, is not immune to SQL injections. SQL injection remains the most severe security threat to web apps and has been for a long time.

In this article, we will go over the details of this deadly attack vector. The topics covered in this article are:

What are SQL queries?

Queries can be used to locate specific data using criteria set by the user. SQL is one language that runs the applications’ databases. It can be used internally by an organization or made public on the internet. SQL queries can find data and perform calculations, summarize data, or automate tasks.

What is SQL injection?

SQL injection is a type of security threat that allows an attacker to manipulate SQL queries sent to the database by the application. The attacker could gain access to data they don’t have permission to. Even worse is the possibility that the attacker could gain write privileges to the database. This allows them to modify or delete data, which can cause severe and long-lasting damage.

SQL injection can be of many types, but all involve an attacker inserting arbitrary SQL in a web application query. User input is the simplest way to inject SQL. User input is usually accepted by web applications via a form. The front-end then passes the input to the back-end database for processing. An attacker could inject SQL into the back-end database to modify, delete, or copy the web application’s content if it fails to sanitize user input properly.

A hacker can also modify cookies to poison a web app’s database query. Cookies save client state information locally. Web applications often load cookies to process this information. Malicious users, or malware, may modify cookies to insert SQL into the back-end databases.

As an attack vector for SQL injection, server variables, such as HTTP headers, can be used. If the web application does not properly sanitize the inputs, forged headers containing arbitrary SQL could inject the code into the database.

The second-order SQL injection attacks, which are not designed to be run immediately but later, are the most sneaky. Even if a developer has sanitized all of their input to protect against an immediate attack, they may still be vulnerable to an SQLi attack if the poisoned data variables are used in a different context.

What are the types of SQL injections?

Generally, SQL injections fall into three categories: In-band or Classic SQLi, Inferential or Blind SQLi, and Out-of-band SQLi. The methods used to access backend information and the damage they can cause can be used to classify SQL injections.

In-band SQLi (Classic)

To launch attacks and gather results, the attacker uses the same channel for communication. It is one of the most popular types of SQLi attacks because of its simplicity and efficiency. This method has two sub-variations:

  1. Error-based: An attacker causes the database to generate error messages by performing specific targeted actions. An attacker could use these error messages to gain information about the structure and configuration of the database.
  2. Union-based: This technique uses the UNION SQL operator to combine multiple select statements from the database into one HTTP response. The attacker may be able to leverage the data in this response.

Inferential SQLi (Blind)

To learn more about the structure of the server, the attacker sends data payloads and monitors its response.

Blind SQL injections are slower than usual because they rely on the behavior patterns and response of the server. However, they can be as dangerous. These are the types of blind SQL injections:

  1. Boolean: The attacker sends a SQL query to the database, prompting the application to return results. Whether the query is true or false will affect the result. The HTTP response’s information will change or remain unchanged based on the result. An attacker can then determine if the message returned a true or false result.
  2. Time-based: The attacker sends a SQL query (using a SQL query) to the database. The database then waits for a time period of seconds before it responds. From the response time of the database, the attacker can determine whether the query is true or false. Based on the result, an HTTP reply will either be generated immediately or after a waiting period. Without relying on the database data, the attacker can determine if the message they sent was true or false.

Out of-band SQLi

This attack can only be carried out if certain features on the web application’s database server are enabled. This attack is used primarily as an alternative to in-band or inferential SQLi.

When the attacker cannot use the same channel to attack and gather information or if a server is too slow to perform these actions, out-of-band SQLi can be used. These techniques depend on the server’s ability to make DNS requests or HTTP requests to send data to an attacker.

Why are SQL injection attacks dangerous?

It is a common misconception that SQL injections are only dangerous if the attacker gets write privileges to the database. This is not true.

An attacker can cause you headaches by simply reading unauthorized information. An attacker could gain access to and expose sensitive information such as financial and personal data. This could damage your company’s reputation and cause problems for your customers and users as the data is sold or shared. This could cause you to be in violation of privacy regulations and have severe financial and legal consequences.

SQL injection attack example

Web applications offer the same functionality as most applications, allowing users to input data in various ways. Malicious individuals can misuse these data entry mechanisms to interfere with the generation and execution of SQL queries.

Watch the video below, which illustrates an SQLi injection example.

How to detect SQL injection attacks?

It is easy to mitigate SQL injection attacks, but even the most skilled developers make mistakes. The key component to mitigating the threat of an SQL injection attack is detection. Although a web application firewall (WAF), can detect and block basic SQL injection attacks it shouldn’t be relied upon as the only preventive measure.

Both network- and host-based intrusion detection systems (IDS) can be set up to detect SQL injection attacks. Network-based IDSes can be used to monitor all connections to your database server and flag suspicious activity. Host-based IDSes can monitor logs from web servers and alert you if something is wrong.

Thankfully, with the right awareness, SQL injection attacks can be easily prevented.

How to prevent SQL injection attacks?

Prepared statements that include parameterized queries: This is a strong safeguard to prevent an attack. Developers are forced by prepared statements to avoid writing dynamic queries, which fail to distinguish between data and application code. Instead, they must use static SQL queries and pass in external input to query. This ensures that the SQL interpreter distinguishes between code and data.

Stored procedures: These are SQL statements that have been defined and stored in a database and can then be called from an application. Developers generally need to create SQL statements that have parameters that can be automatically parameterized. It is possible, though, to create dynamic SQL queries within stored procedures.

Input validation: Maliciously crafted input is a common source of SQL injection. It is best to accept only approved input, a practice known as input validation. There are two types of input validation to protect against it: blocklist validation or allowlist validation.

  • Blocklist validation checks the external input against known malicious inputs. An application compiles all known malicious inputs, then verifies external input against that list. An attacker can create multiple types of malicious input to bypass blacklist validation.
  • Allow listing is an excellent way to reduce risk. Allowlist validation validates an external input against a list of approved inputs. Allowlist input validation ensures that the application understands exactly what it wants and rejects any inputs that fail to pass a test against a known, approved input.

Principle of least privilege: This security measure helps to minimize the damage that a successful attack could cause. Application accounts should not grant DBA and admin access to the database server. Access should always be set to most restricted, depending on their access requirements. Accounts that require only read access will only be granted access to the tables they need. This means that an attacker will not have write access to the database if the application has been compromised.


SQLi attacks can cause severe damage if attackers gain control. This could mean that your website or app is taken down or confidential customer data is leaked.

SQLi attacks are relatively easy to defend against. You must look for SQLi attacks where attackers could inject their own SQL code. Then, you can repair those vulnerabilities with prepared statements, ORMS, or other strategies. Prepared statements may not be available. However, you can fix vulnerabilities by escaping or sanitizing user input before it is passed to the database via a SQL query. Smart database access privileges are a way to reduce the severity and number of SQLi attacks that your app can trigger before it executes queries.

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