# Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') (CWE-22)

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

**Stack:** Go

- Prevalence: 高 頻繁に悪用される
- Impact: クリティカル 1 件の重大度クリティカルなルール
- Prevention: 文書化済み 6 件の修正例

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

## Description

Many file operations are intended to take place within a restricted directory. By using special elements such as '..' and '/' separators, attackers can escape outside of the restricted location to access files or directories that are elsewhere on the system.

## Prevention

2 件の Shoulder 検出ルールに基づく Path Traversal の予防策。

### Go

Resolve the full path and verify it stays within the intended base directory

Validate that extracted archive paths resolve within the target directory

## Consequences

- ファイルまたはディレクトリの読み取り
- ファイルまたはディレクトリの変更
- 未承認コードの実行

## Mitigations

- この脆弱性を発生させない、検証済みのライブラリまたはフレームワークを使用する
- 仕様に厳密に準拠する許可済み入力の許可リストを使用する
- ファイル名には、文字セットを制限する厳格な許可リストを使用する

## Detection

- Total rules: 6
- Critical: 1
- Languages: go, javascript, typescript, python

## Rules by Language

### Go (2 rules)

- **Path Traversal via File Operations** [HIGH]: User input flows to file operations like os.Open without path validation.
  - Remediation: Validate resolved path stays within the base directory.

```go
cleanPath := filepath.Clean(filename)
fullPath := filepath.Join(baseDir, cleanPath)
absPath, _ := filepath.Abs(fullPath)
absBase, _ := filepath.Abs(baseDir)

if !strings.HasPrefix(absPath, absBase+string(os.PathSeparator)) {
    return errors.New("invalid path")
}
```

Learn more: https://shoulder.dev/learn/go/cwe-22/path-traversal
- **Zip Slip / Path Traversal in Archive** [HIGH]: Archive extraction uses filename without validating it stays within target directory.
  - Remediation: Validate extracted paths are within the target directory.

```go
destPath := filepath.Join(destDir, filepath.Clean(f.Name))
if !strings.HasPrefix(destPath, filepath.Clean(destDir)+string(os.PathSeparator)) {
    return errors.New("illegal file path")
}
outFile, _ := os.Create(destPath)
```

Learn more: https://shoulder.dev/learn/go/cwe-22/zip-slip