# 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: Média 3 linguagens cobertas
- Impact: Alto 4 regras de severidade alta
- Prevention: Documentada 4 exemplos de correção

**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

Estratégias de prevenção para Server-Side Request Forgery baseadas em 1 regras de detecção do Shoulder.

### 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

- Ler dados da aplicação
- Burlar mecanismo de proteção
- Executar comandos não autorizados

## Mitigations

- Use uma allowlist dos destinos permitidos
- Desative esquemas de URL desnecessários (file://, gopher://)
- Use segmentação em nível de rede

## 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