Code injection is a cyber attack technique where threat actors insert malicious code into a legitimate application or system through an input mechanism, such as forms, uniform resource locators (URLs), or other data entry points. The code can exploit vulnerabilities in the target system to execute unauthorized actions, compromise data integrity, or gain unauthorized access.

Think of code injection as having a master key crafted to open any door.

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Want to learn more about code injection? Read on.

How Does Code Injection Work?

Let’s take a specific example of Structured Query Language (SQL) injection (SQLi), one of the most common code injection attacks.

Suppose you have a web application with a login form where users enter their username and password to authenticate. The application uses SQL queries to check if the username-password combination matches what is stored in the database. The SQL query can look like this:

SELECT * FROM users WHERE username = ‘input_username’ AND password = ‘input_password’;

In this query, ‘input_username’ and ‘input_password’ are placeholders for the values a user enters.

Now, consider a scenario where attackers want to gain unauthorized access to the application by exploiting a SQLi vulnerability in the login form. They can enter a specially crafted input into the username field to manipulate the SQL query, such as:

username:’ OR 1=1 —

password: any_password

When the application constructs the SQL query with the user input, it looks like this:

SELECT * FROM users WHERE username = ” OR 1=1 –‘ AND password = ‘any_password’;

In this modified query:

  • The single quote () in the attackers’ input closes the username field prematurely. 
  • OR 1=1 is a condition that constantly evaluates to true, effectively bypassing the password check.
  • is a comment symbol in SQL that causes the database to ignore the rest of the query, including the legitimate password check.

As a result, the SQL query returns all records from the user table because the condition 1=1 is always true, effectively granting the attackers access to the application without knowing a valid username or password.

How Code Injection Works

What Are the Kinds of Code Injection Attacks?

There are several types of code injection attacks, including:

  • SQLi: Involves inserting SQL code into input fields to manipulate a database or gain unauthorized access to data.
  • Cross-site scripting (XSS): Involves injecting malicious scripts, usually JavaScript, into web pages viewed by other users. It allows attackers to steal session cookies, redirect users to malicious websites, or perform other malicious actions.
  • Command injection: Involves injecting malicious commands into input fields or parameters passed to system commands or scripts, allowing attackers to execute arbitrary commands on a target system.

How Can You Protect against Code Injection?

Protecting against code injection attacks requires a combination of secure coding practices, robust input validation, and proper security measures at various application layers. Here are some key strategies.

  • Input validation and sanitization: Always validate and sanitize user inputs before using them in dynamic queries, commands, or other interpreted contexts. Ensure that inputs adhere to expected formats and reject any that contain suspicious or potentially malicious characters.
  • Query parameterization: When interacting with databases, use parameterized queries or prepared statements. Parameterized queries separate the SQL code from the data, preventing attackers from injecting malicious SQL code into input fields.
  • Output encoding: Encode user inputs and dynamically generated content before displaying them in web pages or other output mediums. That prevents XSS attacks by neutralizing malicious scripts that can be injected into user-generated content.
  • Least privilege principle application: Limit the permissions and privileges granted to application components. Ensure an application has access only to the resources it needs to function correctly and restrict access to sensitive system resources.
  • Regular security audits and penetration testing: Conduct regular security audits and penetration testing to identify and address application vulnerabilities. Test for various types of code injection attacks, including SQL injection, XSS, command injection, and others.
  • Web application firewall (WAF) usage: Implement a WAF to filter and monitor HyperText Transfer Protocol (HTTP) traffic between an application and the Internet. WAFs can help detect and block common code injection attacks before they reach the application.
  • Software updating and patching: Keep all software, including web servers, application frameworks, and libraries, updated with the latest security patches. Check for security advisories regularly and apply patches promptly to address known vulnerabilities.
  • Security header implementation: Implement security headers, such as Content Security Policy (CSP), to control which resources the browser can load for a web application. CSP can help mitigate the impact of XSS attacks by preventing the execution of unauthorized scripts.
  • Secure development practice: Train developers on secure coding practices and provide them with the tools and resources to write secure code. Encourage code reviews and static code analysis to catch vulnerabilities early in the development life cycle.

Code injection attacks can have severe consequences, including data breaches, unauthorized access to sensitive information, system compromise, and service disruption. To prevent them, developers should implement secure coding practices. WAFs and security testing tools can also help detect and mitigate code injection vulnerabilities.

Key Takeaways