# Improper Output Neutralization for Logs (CWE-117)

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

**Stack:** JavaScript

- Prevalence: Moyenne 3 langages couverts
- Impact: Moyen Revue recommandée
- Prevention: Documentée 4 exemples de correctifs

**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

Stratégies de prévention pour Log Injection basées sur 2 règles de détection Shoulder.

### JavaScript

Strip newline characters from user input before writing to log files

Sanitize user input by stripping CRLF characters before writing to logs

## Warning Signs

- [LOW] user input flowing to persistent log files without sanitization

## Consequences

- Modification des données de l'application
- Dissimuler des activités
- Exécuter du code non autorisé

## Mitigations

- Validez et assainissez toute entrée avant de l'écrire dans les journaux
- Utilisez des formats de log structurés qui séparent les données de la syntaxe du journal
- Encodez les caractères spéciaux lors de l'écriture de données contrôlées par l'utilisateur dans les journaux

## 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

### 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