# Unchecked Return Value (CWE-252)

The product does not check the return value from a method or function, which can prevent it from detecting unexpected states and conditions.

- Prevalence: 中 2 言語をカバー
- Impact: ハイ 1 件の重大度ハイのルール
- Prevention: 文書化済み 2 件の修正例

**OWASP:** Insecure Design (A04:2021-Insecure Design) - #4

## Description

When return values are not checked, the program may continue execution in an error state or with incorrect data, potentially leading to security vulnerabilities.

## Prevention

2 件の Shoulder 検出ルールに基づく Unchecked Return Value の予防策。

### Go

Replace blank identifier _ with err and check error return values

### JavaScript

Always check return values from critical operations like password comparison and database writes

## Warning Signs

- [HIGH] Return value from ... at ... is not checked
- [HIGH] critical operations (file system, database, authentication) whose
return values are not checked

## Consequences

- DoS
- 未承認コードの実行
- アプリケーションデータの変更

## Mitigations

- 関数の戻り値は常にチェックする
- コンパイラ警告を活用して、未チェックの戻り値を検出する
- エラー状態を適切に処理する

## Detection

- Total rules: 2
- Languages: go, javascript, typescript

## Rules by Language

### Go (1 rules)

- **Unchecked Error Return Values** [MEDIUM]: Error return value ignored using blank identifier (_).
  - Remediation: Check all error return values and handle appropriately.

```go
data, err := ioutil.ReadFile(path)
if err != nil {
    return fmt.Errorf("failed to read file: %w", err)
}
```

Learn more: https://shoulder.dev/learn/go/cwe-252/unchecked-errors

### Javascript (1 rules)

- **Unchecked Return Value from Critical Operations** [HIGH]: Detects critical operations (file system, database, authentication) whose
return values are not checked. Ignoring return values can lead to silent
failures, data corruption, and security vulnerabilities.

Critical operations that must have their return values checked include:
- File system operations (write, delete, chmod)
- Database operations (insert, update, delete)
- Authentication/authorization checks
- Cryptographic operations
  - Remediation: Always check return values from critical operations:

```javascript
// ✅ SAFE - Check return value
const result = await fs.writeFile(path, data);
if (!result.success) {
  logger.error('Write failed');
  throw new Error('Failed to write file');
}
```

### Typescript (1 rules)

- **Unchecked Return Value from Critical Operations** [HIGH]: Detects critical operations (file system, database, authentication) whose
return values are not checked. Ignoring return values can lead to silent
failures, data corruption, and security vulnerabilities.

Critical operations that must have their return values checked include:
- File system operations (write, delete, chmod)
- Database operations (insert, update, delete)
- Authentication/authorization checks
- Cryptographic operations
  - Remediation: Always check return values from critical operations:

```javascript
// ✅ SAFE - Check return value
const result = await fs.writeFile(path, data);
if (!result.success) {
  logger.error('Write failed');
  throw new Error('Failed to write file');
}
```