Secure Your Scripts: Avoid Injection

Summary: Sanitize inputs and avoid dangerous code patterns.

In the era of web applications and user-driven content, script injection remains a primary attack vector. A single vulnerability can compromise user data, publish malicious content, or even take control of entire systems. Understanding how to secure your scripts, particularly against injection attacks, is essential for every developer.

What is Script Injection?

Script injection occurs when untrusted inputs are executed as code. The most common type is Cross-Site Scripting (XSS), where attackers inject malicious scripts into pages viewed by other users. Other forms, like SQL Injection or Command Injection, can target databases and operating systems.

For example, consider this JavaScript snippet:

let name = getUserInput();
document.innerHTML = `<h1>Hello, ${name}!</h1>`;

If the user inputs <script>alert('Hacked!')</script>, their code will execute on your page!

Why Injection Attacks Succeed

Injection attacks work because:

  1. Untrusted input is not sanitized or validated.
  2. Dynamic code construction using unsanitized input.
  3. Over-privileged script execution environments.

Key Steps to Avoid Injection

1. Sanitize All Inputs

Always treat input as untrusted. Sanitize both server-side and client-side, as no layer is fully secure on its own.

  • Use well-supported libraries for sanitization (e.g., DOMPurify in JavaScript).
  • Remove or escape characters that might change code behavior (<, >, ", ', etc.).

Example using DOMPurify:

let clean = DOMPurify.sanitize(userInput);
document.innerHTML = `<h1>Hello, ${clean}!</h1>`;

2. Avoid Dangerous Code Patterns

Never use eval() or similar functions with user data

Functions like eval(), new Function(), and setTimeout() with string arguments are dangerous. Attackers can run arbitrary code if these functions process untrusted input.

Don’t do this:

eval("alert('" + userInput + "')");

Use Parameterized APIs

Instead of building SQL or command strings by concatenating inputs, use parameterized queries or APIs that safely bind input.

SQL Example (Node.js/SQLite):

db.run("SELECT * FROM users WHERE username = ?", [username]);

3. Output Encoding

Before displaying user content in HTML, JavaScript, URLs, or CSS, encode it appropriately. Encoding renders inputs as harmless text, not executable code.

HTML example:

  • & → &amp;
  • < → &lt;
  • > → &gt;
  • " → &quot;
  • ' → &#x27;

4. Apply Principle of Least Privilege

Scripts, API keys, and services should operate with the minimum permissions required. If a script doesn’t need filesystem or network access, don’t grant it.

Proactive Tools & Practices

  • Code reviews: Double-check for dangerous patterns and unsanitized input.
  • Security linters: Use tools like eslint-plugin-security.
  • Automated testing: Use security-focused test suites, such as OWASP ZAP.

Real-World Consequences

Even large tech companies have suffered from injection vulnerabilities, leading to data leaks, service disruptions, and loss of user trust. Owning the responsibility for secure code not only protects your product but also your users and reputation.

In Summary

Sanitize, Validate, and Encode. Avoid unsafe code constructs. Favor libraries and frameworks that do the heavy lifting for you. Every layer you secure reduces your exposure to devastating injection attacks.

Security isn’t an afterthought—it’s an essential skill. Secure your scripts, and you secure your future.

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