# 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: 보통 3개 언어 지원
- Impact: 보통 검토 권장
- Prevention: 문서화됨 4개의 수정 예시

**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

2개의 Shoulder 탐지 규칙을 기반으로 한 Open Redirect 예방 전략.

### 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

- 권한 획득
- 보호 메커니즘 우회

## Mitigations

- URL은 신뢰할 수 있는 도메인의 허용 목록을 기준으로 검증하세요
- URL 매개변수를 직접 노출하기보다 매핑 체계를 사용하세요
- 외부 사이트로 리다이렉트하기 전에 경고 페이지를 표시하세요

## 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