# Improper Input Validation (CWE-20)

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

**Stack:** Go

- Prevalence: 高 频繁被利用
- Impact: 高 6 条严重级别为高的规则
- Prevention: 已记录 13 个修复示例

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

## Description

Input validation is a frequently-used technique for checking potentially dangerous inputs in order to ensure that the inputs are safe for processing within the code, or when communicating with other components. When software does not validate input properly, an attacker is able to craft the input in a form that is not expected by the rest of the application.

## Prevention

基于 4 条 Shoulder 检测规则的 Improper Input Validation 预防策略。

### Go

Parse string inputs to typed values and validate against business rules before use

Use Echo struct binding with validation tags instead of untyped maps

Use Fiber BodyParser with typed structs and validation tags

## Warning Signs

- [MEDIUM] Business-critical value used without proper validation
- [MEDIUM] Gin application missing input validation middleware

## Consequences

- 执行未授权代码
- 修改应用程序数据
- 拒绝服务 (DoS)
- 读取应用程序数据

## Mitigations

- 假定所有输入都是恶意的。采用只接受已知良好输入的验证策略
- 进行输入验证时,考虑所有可能相关的属性
- 不要仅依赖于查找恶意或畸形输入

## Detection

- Total rules: 13
- Languages: python, go, javascript, typescript

## Rules by Language

### Go (4 rules)

- **Business Logic Input Validation** [MEDIUM]: Business-critical values (discount, quantity, refund) used without validation.
  - Remediation: Parse and validate business-critical values before use.

```go
discount, err := strconv.ParseFloat(r.FormValue("discount"), 64)
if err != nil || discount < 0 || discount > 100 {
    http.Error(w, "Invalid discount", 400)
    return
}
```

Learn more: https://shoulder.dev/learn/go/cwe-20/input-validation
- **Echo Missing Input Validation** [MEDIUM]: Echo endpoints accepting user input without struct validation.
  - Remediation: Use struct binding with validation tags.

```go
type Input struct {
    Name string `json:"name" validate:"required"`
}

func handler(c echo.Context) error {
    var input Input
    if err := c.Bind(&input); err != nil {
        return c.JSON(400, map[string]string{"error": err.Error()})
    }
    if err := c.Validate(&input); err != nil {
        return c.JSON(400, map[string]string{"error": err.Error()})
    }
    return nil
}
```

Learn more: https://shoulder.dev/learn/go/cwe-20/input-validation
- **Fiber Missing Input Validation** [MEDIUM]: Fiber endpoints accepting user input without struct validation.
  - Remediation: Use BodyParser with struct validation tags.

```go
type Input struct {
    Name string `json:"name" validate:"required"`
}

func handler(c *fiber.Ctx) error {
    var input Input
    if err := c.BodyParser(&input); err != nil {
        return c.Status(400).JSON(fiber.Map{"error": err.Error()})
    }
    if err := validate.Struct(&input); err != nil {
        return c.Status(400).JSON(fiber.Map{"error": err.Error()})
    }
    return nil
}
```

Learn more: https://shoulder.dev/learn/go/cwe-20/input-validation
- **Gin Missing Input Validation** [MEDIUM]: Gin endpoints accepting user input without struct binding validation.
  - Remediation: Use ShouldBindJSON with struct binding tags for validation.

```go
type Input struct {
    Name  string `json:"name" binding:"required,min=2"`
    Email string `json:"email" binding:"required,email"`
}

func handler(c *gin.Context) {
    var input Input
    if err := c.ShouldBindJSON(&input); err != nil {
        c.JSON(400, gin.H{"error": err.Error()})
        return
    }
}
```

Learn more: https://shoulder.dev/learn/go/cwe-20/input-validation