100 Web App Exploits Every Bug Bounty Hunter Should Know

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Introduction

Web application security is a critical field in cybersecurity, with bug bounty hunters playing a key role in identifying vulnerabilities before malicious actors exploit them. This article compiles 100 high-impact web app exploits, covering IDOR, XSS, SSRF, authentication flaws, and more. Whether you’re a penetration tester or a developer, understanding these attack vectors will help secure applications effectively.

Learning Objectives

• Identify common web vulnerabilities such as IDOR, XSS, and SSRF.
• Learn exploitation techniques for authentication and API flaws.
• Understand mitigation strategies to secure web applications.

You Should Know

1. Insecure Direct Object Reference (IDOR) Exploitation

Exploit Command (cURL for IDOR Testing):

curl -X GET "https://example.com/api/user?id=123" -H "Authorization: Bearer [bash]"

Step-by-Step Guide:

1. Intercept a legitimate request (e.g., fetching user data).
2. Modify the `id` parameter to another user’s ID.
3. If unauthorized access is granted, an IDOR vulnerability exists.
   Mitigation: Implement proper access controls and use indirect references.

2. Reflected XSS via Search Bar

Exploit Payload:

<script>alert('XSS')</script>

Step-by-Step Guide:

1. Enter the payload into a search input field.
2. If the script executes in the response, the site is vulnerable.

Mitigation: Sanitize inputs using frameworks like DOMPurify.

3. SSRF in PDF Generator

Exploit Request:

curl -X POST "https://example.com/generate-pdf" -d "url=http://internal-server.local"

Step-by-Step Guide:

1. Submit a PDF generation request with an internal URL.
2. If the server fetches internal resources, SSRF is present.

Mitigation: Restrict URL access via allowlists.

4. JWT Token None Algorithm Bypass

Exploit (Tampered JWT):

{
"alg": "none",
"typ": "JWT"
}

Step-by-Step Guide:

1. Decode a JWT token.

1. Change the algorithm to `none` and remove the signature.
2. Submit the modified token—some servers may accept it.

Mitigation: Enforce algorithm verification.

5. Command Injection via Filename Upload

Exploit Payload:

filename="; whoami;"

Step-by-Step Guide:

1. Upload a file with a malicious filename.

1. If the server executes the command, it’s vulnerable.

Mitigation: Validate and sanitize filenames.

6. GraphQL Introspection Exploitation

Exploit Query:

query { __schema { types { name } } }

Step-by-Step Guide:

1. Send an introspection query to a GraphQL endpoint.
2. If schema details are exposed, attackers can map vulnerabilities.

Mitigation: Disable introspection in production.

7. Open Redirect via Query Parameter

Exploit URL:

https://example.com/redirect?url=https://attacker.com

Step-by-Step Guide:

1. Test redirect parameters with external domains.

1. If the site redirects without validation, it’s vulnerable.

Mitigation: Use allowlists for redirect URLs.

What Undercode Say

• Key Takeaway 1: Many exploits stem from misconfigured access controls (IDOR, JWT flaws).
• Key Takeaway 2: Input validation failures (XSS, command injection) remain prevalent.

Analysis:

Web app security requires proactive testing—automated scanners miss logic flaws. Bug bounty hunters should focus on business logic vulnerabilities (e.g., coupon abuse, race conditions). Future threats will likely exploit AI-driven APIs and serverless misconfigurations, making continuous learning essential.

Prediction

As APIs and cloud services grow, vulnerabilities like SSRF, OAuth misconfigurations, and GraphQL flaws will dominate breaches. Organizations must adopt zero-trust architectures and enforce strict input validation to mitigate risks.

IT/Security Reporter URL:

Reported By: Wesley Thijs – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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