# Improper Neutralization of CRLF Sequences ('CRLF Injection') (CWE-93)

The product uses CRLF (carriage return line feed) as a special element, e.g. to separate headers or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.

**Stack:** Go

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

**OWASP:** Injection (A03:2021-Injection) - #3

## Description

CRLF injection can be used to inject malicious headers in HTTP responses (HTTP response splitting), forge log entries, or manipulate other protocols that use CRLF as a delimiter.

## Prevention

1개의 Shoulder 탐지 규칙을 기반으로 한 CRLF Injection 예방 전략.

### Go

Validate email addresses and reject input containing CRLF characters

## Consequences

- 애플리케이션 데이터 수정
- 승인되지 않은 코드 실행
- 활동 은폐

## Mitigations

- 헤더나 로그에 사용되는 모든 입력에서 CRLF 시퀀스를 제거하거나 인코딩하세요
- 헤더 인코딩을 자동으로 처리하는 프레임워크를 사용하세요
- 입력에 예기치 않은 제어 문자가 포함되어 있지 않은지 검증하세요

## Detection

- Total rules: 3
- Languages: go, javascript, typescript, python

## Rules by Language

### Go (1 rules)

- **Email Header Injection** [HIGH]: User input flows into email headers without CRLF validation.
  - Remediation: Reject input containing CRLF characters and validate email addresses.

```go
func sanitizeHeader(s string) (string, error) {
    if strings.ContainsAny(s, "\r\n") {
        return "", errors.New("invalid characters")
    }
    return s, nil
}

subject, err := sanitizeHeader(r.FormValue("subject"))
if err != nil {
    http.Error(w, "Invalid input", 400)
    return
}
```

Learn more: https://shoulder.dev/learn/go/cwe-93/email-header-injection