✍️ Introduction

Most systems assume something very simple:

"This action will only happen once"

But what if you trigger it…

👉 multiple times at the exact same moment?

That's where Race Conditions come in.

And when they work:

💥 They often lead to financial loss, duplication, or privilege abuse

🧠 What Is a Race Condition

A race condition happens when:

The system fails to handle multiple simultaneous requests correctly

🧪 Simple Example

Application allows:

👉 One coupon per user

You send 5 requests at the same time:

💥 Coupon applied 5 times

🎯 Why Race Conditions Pay So Well

Because they directly affect:

  • 💳 Payments
  • 💰 Refunds
  • 🎟️ Coupons
  • 📦 Orders

👉 Real money = high severity

🔍 Where to Look (Real Mindset)

Think:

👉 "What should only happen once?"

Focus on:

  • Checkout
  • Payments
  • Coupons
  • Account actions
  • Limits / quotas
  • Transfers

📸 Screenshot — Multiple Requests in Burp

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🛠️ Step-by-Step Testing

1. Identify Target Action

Example:

POST /apply-coupon

2. Send to Repeater / Intruder

👉 Prepare multiple identical requests

3. Send Simultaneously

Use:

  • Burp Intruder (parallel requests)
  • Turbo Intruder
  • Repeater (fast send)

4. Analyze Results

If action is applied multiple times:

💥 Race condition confirmed

📸 Screenshot — Duplicate Actions

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⚠️ Common Mistakes

❌ Sending requests too slowly ❌ Testing only once ❌ Not targeting critical actions ❌ Ignoring small inconsistencies

🧠 Pro Techniques (Where Real Bugs Are Found)

🔑 1. Use Parallel Requests

👉 Timing is everything

Requests must hit at the same time

🔑 2. Target Critical Flows

Best targets:

  • Payments
  • Refunds
  • Credits
  • Transfers

🔑 3. Replay Requests

Send same request multiple times:

👉 Check if system processes all of them

🔑 4. Combine With Logic Bugs

Race + Logic flaw:

👉 Extremely powerful

🔑 5. Look for Partial Failures

Even if not fully successful:

👉 Partial duplication = vulnerability

💥 Real Impact Scenario

Application processes refund:

POST /refund
order_id=123

You send 5 requests simultaneously.

System processes all 5:

👉 5 refunds issued

💥 Financial loss → Critical vulnerability

🧭 Why This Matters

Because systems are designed for:

👉 Normal usage

Not:

👉 Abuse under pressure

🚀 What's Next

👉 Final post:

☁️ Cloud & Infrastructure Bugs — Breaking the Backbone of Modern Apps

⚠️ Ethical Use Disclaimer

This content is for educational purposes only.

Only test systems you are authorized to test.

👏 Before You Go

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