Every website you visit is a web application running code on a server somewhere. When that code has vulnerabilities, attackers can exploit them to steal data, hijack accounts, or take control of entire systems. Understanding how websites get hacked is not just for developers. As a user, knowing what can go wrong helps you recognize risk and protect yourself.

The OWASP Top 10: A Map of Web Vulnerabilities

The Open Web Application Security Project (OWASP) maintains a list of the ten most critical web application security risks, updated every few years based on real-world data. This list serves as the standard reference for web security. The current top risks include broken access control, cryptographic failures, injection attacks, insecure design, security misconfiguration, vulnerable components, authentication failures, data integrity failures, logging gaps, and server-side request forgery.

You do not need to memorize the full list, but understanding the most impactful categories gives you a practical mental model for web security threats.

Cross-Site Scripting (XSS)

Cross-Site Scripting occurs when an attacker injects malicious JavaScript into a web page that other users view. Imagine a comment section on a blog where comments are displayed without being sanitized. An attacker posts a comment containing a script that steals the session cookies of everyone who views the page. With those cookies, the attacker can impersonate each victim.

XSS comes in three forms:

  • Stored XSS is the most dangerous. The malicious script is permanently stored on the target server (in a database, comment field, or forum post) and served to every user who views that content.
  • Reflected XSS occurs when the malicious script is embedded in a URL or form submission and reflected back in the server's response. The attacker tricks the victim into clicking a crafted link.
  • DOM-based XSS happens entirely in the browser when client-side JavaScript processes untrusted data and inserts it into the page.

As a user, XSS is particularly insidious because you are visiting a legitimate website. The attack happens within a trusted domain.

SQL Injection

SQL injection exploits websites that build database queries using unsanitized user input. When a login form takes your username and password and directly inserts them into a database query, an attacker can enter specially crafted text that modifies the query itself.

For example, instead of entering a username, an attacker might enter something like ' OR '1'='1, which changes the database query to return all users, bypassing authentication entirely. More destructive payloads can extract the entire database, modify records, or even delete tables.

SQL injection has been responsible for some of the largest data breaches in history, including the 2011 Sony PlayStation Network breach that exposed 77 million accounts and the 2015 TalkTalk breach that compromised 157,000 customer records.

Cross-Site Request Forgery (CSRF)

CSRF tricks a user's browser into making unauthorized requests to a site where the user is already authenticated. If you are logged into your bank and visit a malicious website, that site could contain a hidden form that submits a money transfer request to your bank. Your browser automatically includes your authentication cookies with the request, so the bank thinks you initiated the transfer.

Modern web applications defend against CSRF using anti-forgery tokens: unique, unpredictable values that are included in every form and verified by the server. Without the correct token, the request is rejected even if the user is authenticated.

Broken Authentication

Websites that implement authentication poorly create opportunities for attackers. Common failures include:

  • No rate limiting on login attempts, allowing automated password guessing
  • Weak session management using predictable session IDs or failing to invalidate sessions after logout
  • Password storage failures such as storing passwords in plaintext or using weak hashing algorithms
  • Missing multi-factor authentication for sensitive operations
  • Credential recovery flaws like security questions with guessable answers

The 2024 23andMe breach demonstrated this clearly: attackers used credential stuffing (trying username and password pairs leaked from other sites) and, due to a DNA Relatives sharing feature, parlayed access to 14,000 compromised accounts into data from 6.9 million users.

What This Means for You as a User

You cannot control how well a website is coded, but you can limit your exposure:

  1. Use unique passwords for every site. When a site with weak security is breached, credential stuffing attacks target every other service where you might have reused that password.
  2. Enable two-factor authentication wherever available. Even if your password is compromised through a web application vulnerability, 2FA provides a second layer of defense.
  3. Keep your browser updated. Modern browsers include protections against many web attacks, including XSS filters and same-origin policy enforcement.
  4. Be cautious with links in emails and messages. Reflected XSS and CSRF attacks often begin with a crafted URL sent to the victim.
  5. Monitor your accounts for unauthorized activity. If a site you use is breached, you want to know as quickly as possible. Services like Have I Been Pwned can alert you when your email appears in a breach.
  6. Minimize the data you provide to websites. Every piece of personal information stored by a web application is data that could be exposed in a breach. If a field is not required, leave it blank.

Web application security is a shared responsibility between the developers who build sites and the users who trust them with data. Understanding the attack landscape helps you make better decisions about where you put your information and how you protect your accounts.

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