Unrestricted Access to Sensitive Business Flows: What It Is, How It Happens, and How to Prevent It

When I think of API security, I’m tempted to focus on the "hard" technical flaws. I look for SQL injection where code is improperly sanitized or Broken Authentication where a token is clearly invalid, because these are binary errors. They are either right or wrong.

API6:2023 (Unrestricted Access to Sensitive Business Flows) is different. It is the most deceptive vulnerability on the OWASP list because the request itself often looks perfectly legitimate. The API isn't "broken" in a traditional sense. It is doing exactly what it was designed to do. The problem isn't the code. The problem is the context.

Buying a concert ticket is a standard business flow. Buying 10,000 tickets in 4 seconds is an exploit.

This vulnerability occurs when an API exposes a business process without accounting for how that process could be abused through automation. Common examples include purchasing a product, posting a comment, or reserving a seat. Because the server cannot distinguish between a highly active user and a malicious script, it allows the attacker to exhaust resources, manipulate markets, or degrade the service for everyone else.

Let’s look at three incidents from 2020 to 2025 where this specific vulnerability caused massive disruption.

1. The Ticketmaster Bot Attack (2022)

The most high-profile example of Business Flow abuse in recent history occurred during the presale for Taylor Swift’s "Eras Tour" in November 2022.

How?

Ticketmaster’s API was designed to handle a massive influx of traffic. However, it failed to effectively throttle the specific business flow of reserving tickets.

• The Flow: Verify Code -> Join Queue -> Select Seat -> Reserve Seat.
• The Exploit: Scalpers used bots to bypass the frontend interface and interact directly with the API. These bots aggressively targeted the "Verify Code" and "Join Queue" endpoints. By initiating millions of reservation requests simultaneously, they overwhelmed the system logic.
• The Impact: The API was hit with 3.5 billion system requests, which was four times the previous peak. The system collapsed under the logic weight rather than just the bandwidth. Legitimate fans were unable to access the flow while bots blocked the inventory.

2. The Retail Scalping Crisis (2020-2023)

Between 2020 and 2023, the retail sector faced a persistent API6 crisis involving the sale of high-demand items like PlayStation 5 consoles and NVIDIA GPUs.

How?

Retailers like Best Buy and Walmart exposed APIs for their mobile apps and websites that handled inventory checks and "Add to Cart" flows.

• The Flow: Check Inventory -> Add to Cart -> Checkout.
• The Exploit: Attackers reverse-engineered these private mobile APIs. They discovered that the API endpoints often lacked the same queue protections as the main website. They built "sniper bots" that polled the Check Inventory API endpoint thousands of times per second.
• The Impact: The moment stock was added to the database, the API bots triggered the Add to Cart flow faster than any human UI could render the "Buy" button. This was not a hack of the database. It was unrestricted access to the purchasing flow that allowed scalpers to corner the market and resell goods at 300% markups.

3. Gift Card Redemption Race Conditions (2024)

A more technical variation of this vulnerability involves abusing the logic of rewards programs. This was seen in recent findings regarding gift card implementations.

How?

In 2024, security researchers at Outpost24 detailed a vulnerability (CVE-2024-58248) in the nopCommerce platform that allowed for "double-spending" due to unrestricted flow access.

• The Flow: Validate Code -> Check Balance -> Apply Credit -> Update Balance.
• The Exploit: The API logic checked the balance before deducting it, but it did not lock the flow for a single transaction. Attackers used a "Race Condition" attack. They opened two separate browser sessions and added items to the cart in both. They then submitted the same gift card code in both sessions simultaneously.
• The Impact: Because the API allowed unrestricted concurrent access to the redemption flow, both requests passed the "Check Balance" step before the first request triggered the "Update Balance" step. A single $100 gift card could be redeemed multiple times. This resulted in direct financial theft.

Prevention

Preventing API6:2023 requires understanding the business logic rather than just the code syntax.

1. Device Fingerprinting: Do not rely on IP addresses alone. Use SDKs to fingerprint the client device by checking battery levels or screen resolution to distinguish humans from bots.
2. Business Logic Rate Limiting: Rate limits should not just be generic volume limits like "100 requests per minute." They should be context-aware limits like "1 ticket purchase per user per minute" or "5 inventory checks per hour."
3. Human Detection: Implement CAPTCHA specifically at critical logic gates like Checkout or Reset Password to break automated flows.
4. Flow Analysis: Monitor for impossible speeds. If a user moves from "Add to Cart" to "Checkout" in 30 milliseconds, it is almost certainly a bot.

What Now?

The incidents involving Ticketmaster, retail bots, and gift card fraud all share a common thread: the code worked perfectly, but the logic failed. API6:2023 forces us to stop thinking of security as just a technical checklist. We cannot simply scan our way out of this vulnerability because a scanner sees a valid request; only a human understands a valid intent.

To secure modern applications, we must move beyond securing endpoints and start securing flows. We must ask not just "Is this user allowed to visit this page?" but "Is this user allowed to perform this action at this speed and in this volume?"

Understanding the context of your business is now just as important as understanding the syntax of your code.