# Server-Side Request Forgery (SSRF) (CWE-918)

The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.

**Stack:** Go

- Prevalence: 보통 3개 언어 지원
- Impact: 높음 4개의 높은 심각도 규칙
- Prevention: 문서화됨 4개의 수정 예시

**OWASP:** Server-Side Request Forgery (A10:2021-Server-Side Request Forgery) - #10

## Description

By providing URLs to unexpected hosts or ports, attackers can make it appear that the server is sending the request, possibly bypassing access controls such as firewalls.

## Prevention

1개의 Shoulder 탐지 규칙을 기반으로 한 Server-Side Request Forgery 예방 전략.

### Go

Parse URL and validate host against domain allowlist

## Warning Signs

- [HIGH] user input flowing to HTTP client requests, enabling Server-Side Request Forgery attacks

## Consequences

- 애플리케이션 데이터 읽기
- 보호 메커니즘 우회
- 승인되지 않은 명령 실행

## Mitigations

- 허용된 대상의 허용 목록을 사용하세요
- 필요 없는 URL 스키마(file://, gopher://)는 비활성화하세요
- 네트워크 수준의 세분화(세그멘테이션)를 적용하세요

## Detection

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

## Rules by Language

### Go (1 rules)

- **Server-Side Request Forgery (SSRF)** [HIGH]: Detects user input flowing to HTTP client requests, enabling Server-Side Request Forgery attacks.
  - Remediation: Validate URLs against an allowlist of permitted domains.

```go
allowed := map[string]bool{"api.example.com": true}
parsed, _ := url.Parse(targetURL)
if !allowed[parsed.Host] {
    return errors.New("domain not allowed")
}
```

Learn more: https://shoulder.dev/learn/go/cwe-918/ssrf