# 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:** Go

- Prevalence: 中 3 言語をカバー
- Impact: ハイ 3 件の重大度ハイのルール
- Prevention: 文書化済み 3 件の修正例

**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

1 件の Shoulder 検出ルールに基づく Business Logic Errors の予防策。

### Go

Calculate financial values server-side from trusted data sources instead of accepting client-submitted totals

## Consequences

- 保護メカニズムの回避
- 権限の取得
- アプリケーションデータの変更

## Mitigations

- ビジネスルールとそのセキュリティ上の影響を明確に文書化する
- エッジケースや通常と異なるワークフローもテストする
- すべてのビジネスルールをサーバー側で検証する

## Detection

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

## Rules by Language

### Go (1 rules)

- **Business Logic Bypass** [HIGH]: Client-controlled financial values flow to payment operations without server-side calculation.
  - Remediation: Fetch prices from the database instead of trusting client values.

```go
func checkout(c *gin.Context) {
    productID := c.PostForm("product_id")
    var product Product
    db.First(&product, productID)
    total := product.Price * float64(quantity)
    processPayment(total)
}
```

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