# Business Logic Errors (CWE-840)

The product does not properly implement the business logic rules, which may allow users to manipulate the system in unintended ways.

**Stack:** JavaScript

- Prevalence: Medium 3 languages covered
- Impact: High 3 high-severity rules
- Prevention: Documented 3 fix examples

**OWASP:** Broken Access Control (A01:2021-Broken Access Control) - #1

## Description

Business logic errors occur when the application's implementation doesn't correctly enforce the intended business rules. Unlike technical vulnerabilities, these are flaws in the application's design or logic.

## Prevention

Prevention strategies for Business Logic Errors based on 1 Shoulder detection rules.

### JavaScript

Calculate totals and prices server-side using database values instead of client-submitted data

## Warning Signs

- [HIGH] client-controlled prices or amounts flowing to payment operations without server-side validation

## Consequences

- Bypass Protection Mechanism
- Gain Privileges
- Modify Application Data

## Mitigations

- Clearly document business rules and their security implications
- Test edge cases and unusual workflows
- Implement server-side validation of all business rules

## Detection

- Total rules: 3
- Languages: go, javascript, typescript, python

## Rules by Language

### Javascript (1 rules)

- **Business Logic Bypass** [HIGH]: Detects client-controlled prices or amounts flowing to payment operations without server-side validation.
  - Remediation: Calculate totals server-side using database prices.

```javascript
const product = await Product.findById(productId);
const total = product.price * quantity;
await stripe.charges.create({ amount: total, currency: 'usd' });
```

Learn more: https://shoulder.dev/learn/javascript/cwe-840/business-logic-bypass

### Typescript (1 rules)

- **Business Logic Bypass** [HIGH]: Detects client-controlled prices or amounts flowing to payment operations without server-side validation.
  - Remediation: Calculate totals server-side using database prices.

```javascript
const product = await Product.findById(productId);
const total = product.price * quantity;
await stripe.charges.create({ amount: total, currency: 'usd' });
```

Learn more: https://shoulder.dev/learn/javascript/cwe-840/business-logic-bypass