Top 10 Overlooked Business Logic Flaws in Web Applications

4 min readJan 9, 2025

Web application security often focuses on technical vulnerabilities like SQL injection, cross-site scripting (XSS), and remote code execution. While these are critical, one area that tends to fly under the radar is business logic flaws. These vulnerabilities arise when the application functions correctly from a technical perspective but violates the intended business process, often allowing attackers to manipulate workflows or bypass restrictions.

In this post, we’ll explore five overlooked business logic flaws, real-world examples, and how to mitigate them effectively.

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1. Price Manipulation in E-commerce Platforms

The Flaw: Attackers tamper with client-side parameters, such as the price of an item, during checkout.
Example: Modifying the price in a hidden form field or intercepting it using tools like Burp Suite.
Impact: An attacker could purchase expensive products for pennies.
Mitigation:

Always validate critical parameters (e.g., price, discounts) server-side.

Implement cryptographic signing for sensitive parameters.

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2. Account Takeover via Weak Logic in Password Resets

The Flaw: Exploiting predictable workflows in password reset functionality.
Example: Using incremental tokens or guessing security questions that allow access to another user's account.
Impact: Unauthorized access to accounts, leading to data breaches or financial losses.
Mitigation:

Use unique, time-bound tokens with secure randomness.

Implement multi-factor authentication (MFA) during sensitive workflows.

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3. Exploiting Quantity Limits

The Flaw: Bypassing restrictions on the number of items a user can purchase, redeem, or access.
Example: Exploiting a logic flaw in a promotional code system to redeem unlimited discounts.
Impact: Financial loss, inventory depletion, or abuse of promotional offers.
Mitigation:

Enforce strict server-side validation of user limits.

Monitor suspicious patterns, such as multiple redemptions from the same account.

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4. Privilege Escalation via Flawed Role Management

The Flaw: Improper checks on user roles and permissions.
Example: An attacker modifies a request to access admin-only functionality (e.g., /admin endpoints).
Impact: Unauthorized actions, such as viewing sensitive data or modifying application settings.
Mitigation:

Enforce strict role-based access control (RBAC).

Regularly test all role transitions and privilege boundaries.

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5. Bypassing Multi-Step Workflows

The Flaw: Skipping steps in multi-step processes, such as order approval or payment confirmation.
Example: Directly accessing the final URL of a multi-step process without completing previous steps.
Impact: Completing restricted actions (e.g., placing an order without paying).
Mitigation:

Use server-side tracking of workflow progress.

Require each step to be completed sequentially with proper state validation.

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6. Mass Assignment Exploitation

The Flaw: Allowing attackers to modify unintended fields by passing additional parameters in requests.
Example: A user updates their account role to "admin" by including role=admin in a POST request.
Impact: Unauthorized access or privilege escalation.
Mitigation:

Use allowlists for editable fields.

Reject unexpected parameters server-side.

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7. Insecure Direct Object References (IDOR)

The Flaw: Exposing internal object references (e.g., user IDs) without proper access controls.
Example: Modifying a URL parameter like /invoice/123 to /invoice/124 to view another user's invoice.
Impact: Unauthorized access to sensitive data.
Mitigation:

Enforce access controls at the object level.

Use opaque identifiers instead of direct references.

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8. Discount Abuse in Coupon Systems

The Flaw: Exploiting logic flaws in coupon redemption systems.
Example: Using expired or already-redeemed coupons multiple times by modifying requests.
Impact: Financial losses due to misuse of promotions.
Mitigation:

Implement one-time use tokens for coupons.

Validate coupon expiration and redemption limits server-side.

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9. Session Fixation Attacks

The Flaw: Reusing a session ID to hijack another user’s session.
Example: An attacker sends a victim a link with a pre-set session ID, then logs in using the same ID after the victim authenticates.
Impact: Unauthorized account access.
Mitigation:

Regenerate session IDs upon login.

Use secure, unique session tokens.

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10. Order of Operations Exploitation

The Flaw: Performing actions out of order to achieve unintended outcomes.
Example: Canceling an order after receiving the product but before the payment is processed.
Impact: Loss of revenue or inventory.
Mitigation:

Implement atomic transactions for multi-step processes.

Log and monitor unexpected behavior patterns.

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Why Are Business Logic Flaws Overlooked?

Unlike technical vulnerabilities, business logic flaws are application-specific. They require a deep understanding of how the system is designed to function and how it could be abused. These flaws often go unnoticed in automated vulnerability scans, making them a critical area for manual testing and threat modeling.

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Business logic flaws can be as dangerous as technical vulnerabilities, yet they’re often overlooked during security assessments. By understanding these vulnerabilities and implementing proper controls, you can significantly enhance your web application’s resilience against attacks.

Have you encountered any interesting business logic flaws during your bug bounty hunting or pentesting journey? Share your experience in the comments or tweet me at @Spectatorguy.