# 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: 높음 자주 악용됨
- Impact: 치명적 1개의 치명적 심각도 규칙
- Prevention: 문서화됨 6개의 수정 예시

**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

2개의 Shoulder 탐지 규칙을 기반으로 한 Path Traversal 예방 전략.

### 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

- 파일 또는 디렉터리 읽기
- 파일 또는 디렉터리 수정
- 승인되지 않은 코드 실행

## Mitigations

- 이러한 약점이 발생하지 않도록 검증된 라이브러리나 프레임워크를 사용하세요
- 사양을 엄격히 준수하는 허용 가능한 입력의 허용 목록(allowlist)을 사용하세요
- 파일 이름에는 문자 집합을 제한하는 엄격한 허용 목록을 사용하세요

## 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