Common Web Vulnerabilities and How to Prevent Them

Building a secure web application is as important as building a functional one. A single vulnerability can lead to data breaches, loss of user trust, and significant financial damage. Here are some of the most common web vulnerabilities and how to defend against them.

1. Cross-Site Scripting (XSS)

XSS occurs when an attacker injects malicious scripts into a web page viewed by other users. This script can then steal user information (like cookies or session tokens) or perform actions on behalf of the user.

• Prevention:
  • Output Encoding: The primary defense is to encode any user-generated content before rendering it in the browser. This treats the content as text, not as executable code. Libraries like React automatically do this for JSX content.
  • Content Security Policy (CSP): A CSP is an HTTP header that tells the browser which sources of content (scripts, styles, images) are trusted. This can prevent the browser from executing malicious scripts from untrusted sources.

2. SQL Injection (SQLi)

SQLi happens when an attacker can manipulate the SQL queries your application makes to its database. This can allow them to view, modify, or delete data they shouldn't have access to.

• Prevention:
  • Prepared Statements (Parameterized Queries): This is the most effective defense. Instead of building queries with string concatenation, you use placeholders for user input. The database driver then separates the query logic from the user data, making it impossible for the input to be treated as part of the SQL command.
  • Use an ORM: Object-Relational Mapping libraries (like Prisma or Sequelize) often handle this for you, but it's still crucial to use their query-building methods correctly.

3. Cross-Site Request Forgery (CSRF)

CSRF (or XSRF) tricks a logged-in user into submitting a malicious request to a web application they are authenticated with. For example, a user might click a link on a malicious site that secretly triggers a "transfer funds" request on their banking website.

• Prevention:
  • Anti-CSRF Tokens: The server generates a unique, unpredictable token for each user session. This token must be included in any state-changing request (like a form submission). The server then validates this token before executing the request. Since the attacker's site cannot guess this token, the forged request will fail.
  • SameSite Cookies: The SameSite cookie attribute can be set to Strict or Lax to control whether cookies are sent with cross-site requests, providing another layer of defense.

Web security is a continuous process, not a one-time checklist. By understanding these common threats and implementing robust defenses, you can build applications that protect both your business and your users.