# URL Redirection to Untrusted Site ('Open Redirect') (CWE-601)

A web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a Redirect.

**Stack:** JavaScript

- Prevalence: 中 3 言語をカバー
- Impact: ミディアム レビュー推奨
- Prevention: 文書化済み 4 件の修正例

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

## Description

An open redirect vulnerability occurs when an application takes user input and uses it to redirect the user to a different URL. Attackers can exploit this to redirect users to malicious sites.

## Prevention

2 件の Shoulder 検出ルールに基づく Open Redirect の予防策。

### JavaScript

Validate redirect targets against an allowlist of permitted paths

Validate redirect URLs against an allowlist or enforce relative paths

## Warning Signs

- [MEDIUM] user-controlled input flowing into redirect targets in Next
- [MEDIUM] user input flowing into redirect functions without URL validation

## Consequences

- 権限の取得
- 保護メカニズムの回避

## Mitigations

- URL は信頼できるドメインの許可リストと照合して検証する
- 直接的な URL パラメータではなく、マッピングシステムを使用する
- 外部サイトへリダイレクトする前に警告ページを表示する

## Detection

- Total rules: 4
- Languages: go, javascript, typescript, python

## Rules by Language

### Javascript (2 rules)

- **Next.js Open Redirect** [MEDIUM]: Detects user-controlled input flowing into redirect targets in Next.js middleware.
  - Remediation: Validate redirect targets against an allowlist of permitted paths.

```typescript
const ALLOWED_PATHS = ['/login', '/dashboard', '/profile'];
const redirect = request.nextUrl.searchParams.get('redirect');

if (redirect && ALLOWED_PATHS.includes(redirect)) {
  return NextResponse.redirect(new URL(redirect, request.url));
}
return NextResponse.redirect(new URL('/', request.url));
```

Learn more: https://shoulder.dev/learn/javascript/cwe-601/nextjs-open-redirect
- **Open Redirect via Untrusted URLs** [MEDIUM]: Detects user input flowing into redirect functions without URL validation.
  - Remediation: Validate redirect URLs against an allowlist or ensure they are relative paths.

```javascript
const ALLOWED = ['/home', '/dashboard', '/profile'];
if (ALLOWED.includes(url) || url.startsWith('/')) {
  res.redirect(url);
}
```

Learn more: https://shoulder.dev/learn/javascript/cwe-601/open-redirect

### Typescript (2 rules)

- **Next.js Open Redirect** [MEDIUM]: Detects user-controlled input flowing into redirect targets in Next.js middleware.
  - Remediation: Validate redirect targets against an allowlist of permitted paths.

```typescript
const ALLOWED_PATHS = ['/login', '/dashboard', '/profile'];
const redirect = request.nextUrl.searchParams.get('redirect');

if (redirect && ALLOWED_PATHS.includes(redirect)) {
  return NextResponse.redirect(new URL(redirect, request.url));
}
return NextResponse.redirect(new URL('/', request.url));
```

Learn more: https://shoulder.dev/learn/javascript/cwe-601/nextjs-open-redirect
- **Open Redirect via Untrusted URLs** [MEDIUM]: Detects user input flowing into redirect functions without URL validation.
  - Remediation: Validate redirect URLs against an allowlist or ensure they are relative paths.

```javascript
const ALLOWED = ['/home', '/dashboard', '/profile'];
if (ALLOWED.includes(url) || url.startsWith('/')) {
  res.redirect(url);
}
```

Learn more: https://shoulder.dev/learn/javascript/cwe-601/open-redirect