# 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:** JavaScript

- Prevalence: 高 频繁被利用
- Impact: 关键 1 条严重级别为关键的规则
- Prevention: 已记录 6 个修复示例

**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

基于 2 条 Shoulder 检测规则的 Path Traversal 预防策略。

### JavaScript

Use path.basename() to strip directory components or validate resolved paths stay within allowed directories

Validate that extracted archive entry paths resolve within the target directory before writing

## Warning Signs

- [HIGH] unsafe extraction of zip/tar archives without path validation,
which can lead to arbitrary file writ
- [CRITICAL] untrusted user input used in file system operations without proper validation

## Consequences

- 读取文件或目录
- 修改文件或目录
- 执行未授权代码

## Mitigations

- 使用经过审查的库或框架,以防止此弱点出现
- 使用严格符合规范的可接受输入的允许列表
- 对于文件名,使用限制字符集的严格允许列表

## Detection

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

## Rules by Language

### Javascript (2 rules)

- **Path Traversal in File Operations** [CRITICAL]: Detects untrusted user input used in file system operations without proper validation.
This can allow attackers to read or write arbitrary files on the server.
  - Remediation: Use path.basename() to extract filenames or validate resolved paths stay within allowed directories.

```javascript
const safeName = path.basename(userInput);
const filePath = path.join(__dirname, 'uploads', safeName);
fs.readFile(filePath, callback);
```

Learn more: https://shoulder.dev/learn/javascript/cwe-22/path-traversal
- **Zip Slip Path Traversal** [HIGH]: Detects unsafe extraction of zip/tar archives without path validation,
which can lead to arbitrary file writes via path traversal (Zip Slip).

Zip Slip is a form of path traversal attack where a malicious archive contains
entries with paths like "../../../etc/passwd" that escape the intended extraction
directory and overwrite arbitrary files on the system.

Vulnerable patterns:
1. Extracting zip entries without validating the extracted path
2. Not checking if extracted path is inside target dire
  - Remediation: Validate extracted paths are inside the target directory:

```javascript
const path = require('path');

function isPathSafe(baseDir, targetPath) {
  const resolvedBase = path.resolve(baseDir);
  const resolvedTarget = path.resolve(baseDir, targetPath);
  return resolvedTarget.startsWith(resolvedBase + path.sep);
}

for (const entry of zip.getEntries()) {
  if (!isPathSafe(targetDir, entry.entryName)) {
    throw new Error('Path traversal attempt');
  }
  zip.extractEntryTo(entry, targetDir, false, true);
}
```

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

### Typescript (2 rules)

- **Path Traversal in File Operations** [CRITICAL]: Detects untrusted user input used in file system operations without proper validation.
This can allow attackers to read or write arbitrary files on the server.
  - Remediation: Use path.basename() to extract filenames or validate resolved paths stay within allowed directories.

```javascript
const safeName = path.basename(userInput);
const filePath = path.join(__dirname, 'uploads', safeName);
fs.readFile(filePath, callback);
```

Learn more: https://shoulder.dev/learn/javascript/cwe-22/path-traversal
- **Zip Slip Path Traversal** [HIGH]: Detects unsafe extraction of zip/tar archives without path validation,
which can lead to arbitrary file writes via path traversal (Zip Slip).

Zip Slip is a form of path traversal attack where a malicious archive contains
entries with paths like "../../../etc/passwd" that escape the intended extraction
directory and overwrite arbitrary files on the system.

Vulnerable patterns:
1. Extracting zip entries without validating the extracted path
2. Not checking if extracted path is inside target dire
  - Remediation: Validate extracted paths are inside the target directory:

```javascript
const path = require('path');

function isPathSafe(baseDir, targetPath) {
  const resolvedBase = path.resolve(baseDir);
  const resolvedTarget = path.resolve(baseDir, targetPath);
  return resolvedTarget.startsWith(resolvedBase + path.sep);
}

for (const entry of zip.getEntries()) {
  if (!isPathSafe(targetDir, entry.entryName)) {
    throw new Error('Path traversal attempt');
  }
  zip.extractEntryTo(entry, targetDir, false, true);
}
```

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