# Improper Output Neutralization for Logs (CWE-117)

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

**Stack:** Python

- Prevalence: Medium 3 languages covered
- Impact: Medium Review recommended
- Prevention: Documented 4 fix examples

**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

Prevention strategies for Log Injection based on 1 Shoulder detection rules.

### Python

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

## Warning Signs

- [MEDIUM] user input flowing directly into log messages without sanitization

## Consequences

- Modify Application Data
- Hide Activities
- Execute Unauthorized Code

## Mitigations

- Validate and sanitize all input before writing to logs
- Use structured logging formats that separate data from log syntax
- Encode special characters when writing user-controlled data to logs

## Detection

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

## Rules by Language

### 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