# Improper Output Neutralization for Logs (CWE-117)

The product does not neutralize or incorrectly neutralizes output that is written to logs.

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

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

## Description

Log injection attacks occur when user input is written to log files without proper sanitization. This can allow attackers to forge log entries, inject malicious content, or exploit log analysis tools.

## Prevention

4개의 Shoulder 탐지 규칙을 기반으로 한 Log Injection 예방 전략.

### Go

Strip newlines and control characters from user input before logging

### JavaScript

Strip newline characters from user input before writing to log files

Sanitize user input by stripping CRLF characters before writing to logs

### Python

Use structured logging with separate fields for user data instead of string interpolation

## Warning Signs

- [MEDIUM] unsanitized user input flowing into log statements, enabling log forging attacks
- [MEDIUM] user input flowing directly into log messages without sanitization
- [LOW] user input flowing to persistent log files without sanitization

## Consequences

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

## Mitigations

- 로그에 기록하기 전에 모든 입력을 검증하고 정제하세요
- 데이터와 로그 구문을 분리하는 구조화된 로그 포맷을 사용하세요
- 사용자가 제어할 수 있는 데이터를 로그에 기록할 때 특수 문자를 인코딩하세요

## Detection

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

## Rules by Language

### Javascript (2 rules)

- **Log Injection** [LOW]: Detects user input flowing to persistent log files without sanitization.
  - Remediation: Sanitize user input by removing newline characters before logging.

```javascript
const safe = userInput.replace(/[\r\n]/g, '');
logger.info(safe);
```

Learn more: https://shoulder.dev/learn/javascript/cwe-117/log-injection
- **Log Injection** [MEDIUM]: Detects user input flowing to persistent log files without sanitization.
  - Remediation: Sanitize user input before logging to prevent log forgery:

```javascript
const sanitize = (str) => str.replace(/[\r\n]/g, '').substring(0, 200);
logger.info('Login attempt', { username: sanitize(req.body.username) });
```

Learn more: https://shoulder.dev/learn/javascript/cwe-117/log-injection

### Go (1 rules)

- **Log Injection / Log Forging** [MEDIUM]: Detects unsanitized user input flowing into log statements, enabling log forging attacks.
  - Remediation: Remove newlines and control characters from user input before logging.

```go
sanitized := strings.ReplaceAll(userInput, "\n", "")
sanitized = strings.ReplaceAll(sanitized, "\r", "")
log.Printf("User action: %s", sanitized)
```

Learn more: https://shoulder.dev/learn/go/cwe-117/log-injection

### Typescript (1 rules)

- **Log Injection** [MEDIUM]: Detects user input flowing to persistent log files without sanitization.
  - Remediation: Sanitize user input before logging to prevent log forgery:

```javascript
const sanitize = (str) => str.replace(/[\r\n]/g, '').substring(0, 200);
logger.info('Login attempt', { username: sanitize(req.body.username) });
```

Learn more: https://shoulder.dev/learn/javascript/cwe-117/log-injection

### Python (1 rules)

- **Log Injection / Log Forging** [MEDIUM]: Detects user input flowing directly into log messages without sanitization.
  - Remediation: Use structured logging with separate fields for user data.

```python
logging.info("Login attempt", extra={'username': username})
```

Learn more: https://shoulder.dev/learn/python/cwe-117/log-injection