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Back to Internet & Web Basics
Lesson 35 of 50

What Are Common Web Vulnerabilities? A Complete Overview for Web Security Foundations

Common web vulnerabilities are weaknesses in web applications, servers, or configurations that attackers can exploit to steal data, take control of accounts, disrupt services, or compromise entire systems. Because web applications are publicly accessible, even small mistakes in code or configuration can have serious consequences. Most web attacks do not rely on advanced hacking techniques—they exploit predictable, well-known vulnerabilities such as poor input validation, weak authentication, insecure session handling, or misconfigured servers. These issues appear repeatedly across applications, which is why security frameworks and standards emphasize understanding common vulnerability patterns. This overview explains the most important web vulnerabilities every student, developer, and security-conscious professional must understand. Instead of just listing attack names, it focuses on how each vulnerability works, why it happens, what damage it causes, and how it is commonly prevented. The goal is to build strong mental models that help you recognize vulnerabilities early—during design and development—rather than after an attack.

What Is a Web Vulnerability?

A web vulnerability is a weakness in a web application or its supporting infrastructure that allows an attacker to perform unauthorized actions. These actions may include accessing sensitive data, executing malicious code, or disrupting service availability.

Most vulnerabilities arise from a combination of:

  • Trusting user input
  • Improper access control
  • Insecure defaults or misconfiguration
  • Lack of security testing

Why Common Vulnerabilities Keep Appearing

Despite being well-documented, common vulnerabilities continue to appear because security is often treated as an afterthought.

  • Fast development cycles
  • Complex application architectures
  • Third-party dependencies
  • Insufficient security awareness

Injection Attacks

SQL Injection

SQL Injection occurs when attackers insert malicious SQL commands into user input that is directly used in database queries.

This allows attackers to:

  • Read sensitive database data
  • Modify or delete records
  • Bypass authentication

Root cause: unsanitized input combined with dynamic query construction.

Command Injection

Command injection allows attackers to execute system-level commands on the server by abusing vulnerable input handling.

Cross-Site Scripting (XSS)

Cross-Site Scripting occurs when malicious scripts are injected into web pages and executed in a victim’s browser.

Types of XSS

  • Stored XSS: Script stored on the server
  • Reflected XSS: Script reflected in a response
  • DOM-based XSS: Script executed via client-side logic

Impact includes session hijacking, credential theft, and malicious redirects.

Cross-Site Request Forgery (CSRF)

CSRF tricks authenticated users into performing unintended actions by exploiting trust between the browser and the server.

For example, a logged-in user may unknowingly submit a request to change account settings or initiate a transaction.

Broken Authentication

Broken authentication vulnerabilities occur when login mechanisms, password storage, or session management are implemented incorrectly.

  • Weak or reused passwords
  • Missing multi-factor authentication
  • Predictable session tokens

Attackers exploit these weaknesses to take over user accounts.

Broken Access Control

Broken access control allows users to perform actions outside their intended permissions.

Examples include:

  • Accessing another user’s data
  • Privilege escalation
  • Insecure direct object references (IDOR)

Security Misconfiguration

Security misconfiguration occurs when systems are deployed with insecure default settings or unnecessary features enabled.

  • Exposed admin panels
  • Open cloud storage buckets
  • Verbose error messages

Sensitive Data Exposure

Sensitive data exposure happens when applications fail to properly protect confidential information.

  • Missing HTTPS
  • Weak encryption
  • Storing plaintext passwords

Using Vulnerable Components

Modern applications rely heavily on third-party libraries. If these dependencies contain known vulnerabilities, the entire application becomes vulnerable.

This includes:

  • Outdated frameworks
  • Unpatched plugins
  • Insecure libraries

Denial of Service (DoS and DDoS)

Denial of Service attacks aim to make applications unavailable by overwhelming them with traffic or resource-heavy requests.

While availability is the target, DoS attacks often expose scaling and rate-limiting weaknesses.

Comparison of Common Web Vulnerabilities

Vulnerability Main Cause Primary Impact
SQL Injection Unvalidated input Data compromise
XSS Unescaped output Session hijacking
CSRF Missing request validation Unauthorized actions
Broken Authentication Weak login/session logic Account takeover
Security Misconfiguration Unsafe defaults System exposure

Defense-in-Depth Approach

No single security control can prevent all vulnerabilities. Modern web security relies on layered defenses.

  • Secure coding practices
  • Input validation and output encoding
  • Authentication and authorization controls
  • Web Application Firewalls (WAF)
  • Monitoring and logging

Real-World Perspective

Most major data breaches result from well-known vulnerabilities, not unknown exploits. Organizations that understand and address common web vulnerabilities early dramatically reduce risk.

Summary

Common web vulnerabilities represent recurring failure patterns in web systems. By understanding how these vulnerabilities work and why they occur, developers and security teams can build safer applications, detect issues earlier, and respond effectively to threats. This knowledge forms the foundation of all modern web security practices.