# 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: 높음 자주 악용됨
- Impact: 높음 6개의 높은 심각도 규칙
- Prevention: 문서화됨 13개의 수정 예시

**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

4개의 Shoulder 탐지 규칙을 기반으로 한 Improper Input Validation 예방 전략.

### 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

- 승인되지 않은 코드 실행
- 애플리케이션 데이터 수정
- DoS
- 애플리케이션 데이터 읽기

## Mitigations

- 모든 입력이 악의적이라고 가정하세요. 알려진 안전한 입력만 허용하는 검증 전략을 사용하세요
- 입력 검증 시 관련될 수 있는 모든 속성을 고려하세요
- 악성 또는 잘못된 형식의 입력을 찾는 것에만 의존하지 마세요

## 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