Common Web Application Vulnerabilities and How to Mitigate Them

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Introduction

Web applications are increasingly targeted by attackers due to common security oversights. Ethical hacker Arnesh Vaidya recently highlighted four critical vulnerabilities found in a single application, demonstrating how easily security flaws can be exploited. This article examines these vulnerabilities, provides mitigation techniques, and offers actionable commands for security professionals.

Learning Objectives

  • Understand common web app vulnerabilities (JWT exposure, input validation bypass, geo-restriction evasion, privilege escalation).
  • Learn how to test and patch these vulnerabilities using verified commands.
  • Implement secure coding practices to prevent similar exploits.

You Should Know

1. JWT Token Exposure in API Responses

Vulnerability: Forgot-password codes leaked in JWT responses.

Mitigation:

 Use jwt_tool to test JWT security (Linux) 
jwt_tool <JWT_TOKEN> -T

Steps:

  1. Inspect API responses for sensitive data in JWTs using browser dev tools or curl.

2. Use `jwt_tool` to analyze token integrity.

  1. Configure the backend to never return sensitive data in JWTs.

2. Bypassing Input Validation via Special Characters

Vulnerability: Attackers bypassed signup restrictions using special characters.

Mitigation:

 Python regex for strict input validation 
import re 
if not re.match("^[a-zA-Z0-9_]+$", username): 
raise ValueError("Invalid username")

Steps:

1. Audit input validation logic for blacklist gaps.

2. Use whitelist-based regex (e.g., above) for usernames/passwords.

3. Test with payloads like `admin’–` or `