# Improper Output Neutralization for Logs (CWE-117)

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

- Prevalence: Média 3 linguagens cobertas
- Impact: Médio Revisão recomendada
- Prevention: Documentada 4 exemplos de correção

**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

Estratégias de prevenção para Log Injection baseadas em 4 regras de detecção do Shoulder.

### 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

- Modificar dados da aplicação
- Ocultar atividades
- Executar código não autorizado

## Mitigations

- Valide e sanitize toda entrada antes de gravar em logs
- Use formatos de log estruturados que separem dados da sintaxe do log
- Codifique caracteres especiais ao gravar dados controlados pelo usuário em logs

## 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