After spending more than three years in web security and bug bounty hunting, I've learned one important lesson the hard way: most real vulnerabilities are not hidden in complex exploits. They are usually simple, repeatable mistakes.
When I started, I wasted months chasing advanced attacks while missing basic issues right in front of me. Over time, by reading real reports, testing production applications, and failing more times than I can count, I realized something surprising.
A huge percentage of valid bug bounty reports come from just four vulnerability types.
If you truly understand these four, you don't need to know everything. You just need to know these well.
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## 1. Insecure Direct Object References (IDOR)
IDOR is one of the most dangerous and most ignored vulnerabilities in modern applications.
### What It Is IDOR happens when an application allows users to access data by changing an identifier, without properly checking whether they are authorized to see it.
### Simple Example
A normal request looks like this: ``` /api/user/profile?id=123 ```
An attacker changes the ID: ``` /api/user/profile?id=124 ```
If the server responds with another user's data, that's an IDOR.
### Why It Happens
- Developers confuse authentication with authorization - APIs are rushed into production - Object-level access control is forgotten
# Impact
- Exposure of sensitive user data - Privacy violations - High-severity data breaches
# How I Test for IDOR
- Modify IDs in URLs, headers, and request bodies - Test both numeric and UUID values - Access other users' resources after login - Watch for patterns like `/api/users/{id}`
IDOR doesn't make noise. That's why it works.
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## 2. Cross-Site Scripting (XSS)
XSS is old, well-known, and still everywhere.
# What It Is
XSS allows attackers to inject JavaScript into pages viewed by other users.
# Real-World Scenario
An input accepts: ``` <script>alert(1)</script> ```
And the browser executes it.
That's all it takes.
# Why XSS Still Exists
- Input validation is inconsistent - Output encoding is skipped - Developers rely too much on frameworks
# Impact
- Session hijacking - Cookie theft - Account takeover - Malicious redirects
# How I Approach XSS
- Test every input, even "harmless" ones - Check reflected parameters in responses - Analyze frontend JavaScript for DOM sinks - Start simple before trying complex payloads
XSS rewards patience, not creativity.
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# 3. CORS Misconfigurations
CORS vulnerabilities are misunderstood, which makes them valuable.
# What It Is
CORS misconfiguration allows unauthorized websites to make authenticated requests to an application.
# Dangerous Configuration ``` Access-Control-Allow-Origin: * Access-Control-Allow-Credentials: true ```
This combination can expose private user data.
# Why Developers Get It Wrong
- Enabled during testing and never fixed - Security impact is unclear - Defaults are left unchanged
# Impact
- Theft of authenticated user data - Unauthorized API access - Bypass of same-origin protections
# How I Test CORS
- Inspect response headers on APIs - Change Origin headers manually - Test credentialed requests - Analyze preflight (OPTIONS) responses
CORS bugs often look boring. Until they aren't.
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# 4. Security Misconfigurations
This is where many serious breaches begin.
# What It Is
Security misconfiguration happens when applications are deployed with unsafe defaults or forgotten settings.
# Common Findings
- Exposed `.git` or `.env` files - Debug mode enabled in production - Default credentials left unchanged - Directory listing enabled - Missing security headers
# Why It Happens
- Fast releases - No security checklist - Copy-paste deployments - "We'll fix it later" mindset
# Impact
- Information disclosure - Unauthorized access - Complete system compromise
# How I Look for Misconfigurations
- Check common files and directories - Review response headers - Look for verbose error messages - Test admin panels and backups
Misconfigurations are not advanced, but they are effective.
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## Learning Path I Recommend
*Weeks 1–2:** Focus only on IDOR Understand authorization deeply.
*Weeks 3–4:** Learn XSS properly Reflected, stored, and DOM-based.
*Weeks 5–6:** Study CORS behavior Read specs, not just blog posts.
*Weeks 7–8:** Hunt misconfigurations Build your own checklist.
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## Final Thoughts
These four vulnerabilities are not exciting. They are not new. They are not complex.
But they work.
After years of testing, I can confidently say that consistency beats sophistication. Most applications don't fail because of advanced attacks. They fail because of basic mistakes that nobody checks carefully.
Master these four, and you will find bugs. Not occasionally. Consistently.
That's what really matters in bug bounty hunting.
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