target_url = "http://target.hackviser.com/api/transfer"
If you can send two requests simultaneously, you can trick the server. The first request starts the "Check" and sees you have 100 credits. Before it can deduct the credits ("Use"), the second request also starts the "Check." Because the first request hasn't finished yet, the second request also sees 100 credits. Both requests pass the check, and you effectively spend 100 credits twice to get two items (double spending).
def redeem_coupon(user_id, code): with db.transaction(): coupon = db.query("SELECT * FROM coupons WHERE code = %s FOR UPDATE", code) if not coupon or coupon.used: return "Invalid" db.execute("UPDATE coupons SET used = TRUE WHERE code = %s", code) db.execute("UPDATE users SET balance = balance + %s WHERE id = %s", coupon.value, user_id) return "Success" race condition hackviser
In the world of computer security, there's a fascinating phenomenon that can be both a blessing and a curse: the race condition. As a hacker, understanding and exploiting race conditions can be a powerful tool in your arsenal. But what exactly is a race condition, and how can you use it to your advantage?
A is a subtle yet high-impact vulnerability that occurs when a system’s behavior depends on the uncontrolled sequence or timing of concurrent events. While many developers treat them as rare glitches, platforms like Hackviser highlight them as critical business logic flaws that allow attackers to bypass limits, escalate privileges, or corrupt data. What is a Race Condition? target_url = "http://target
threads = [] for _ in range(20): t = threading.Thread(target=attack) t.start() threads.append(t)
def attack(): for _ in range(5): requests.post(url, json=data, headers=headers) Both requests pass the check, and you effectively
In modern computing, multiple threads or processes often access shared resources simultaneously to improve performance. A race condition vulnerability arises when the system fails to coordinate this access, creating a — a brief period where a resource is in an inconsistent state. The Classic Example: Double Withdrawal
As a developer, it's essential to take steps to prevent race conditions:
Imagine a banking application with a $100 balance. An attacker sends two simultaneous withdrawal requests for $100: What Is a Race Condition? Types, Causes & Security Impact