# Improper Handling of Extra Parameters (CWE-235)

The product does not handle or incorrectly handles when the number of parameters, fields, or arguments with the same name exceeds the expected amount.

- Prevalence: Mittel 2 Sprachen abgedeckt
- Impact: Mittel Review empfohlen
- Prevention: Dokumentiert 2 Fix-Beispiele

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

## Description

When applications receive duplicate parameters, they may process them inconsistently, leading to security bypasses or logic errors. Different frameworks may select the first, last, or combine duplicate parameters.

## Prevention

Präventionsstrategien für Improper Handling of Extra Parameters basierend auf 2 Shoulder-Erkennungsregeln.

### JavaScript

Add hpp middleware to normalize duplicate query parameters

### Python

Explicitly check for and reject duplicate HTTP parameters

## Warning Signs

- [MEDIUM] handling of duplicate HTTP parameters without proper validation
- [LOW] Request parameters used without HPP protection.
Express converts duplicate query/body params to arrays, which can bypass
- [LOW] missing HTTP Parameter Pollution (HPP) protection in Express

## Consequences

- Schutzmechanismus umgehen
- Anwendungsdaten ändern

## Mitigations

- Eine Richtlinie für den Umgang mit doppelten Parametern festlegen und durchsetzen
- Anfragen mit doppelten sicherheitsrelevanten Parametern ablehnen
- Verwende Frameworks, die Duplikate konsistent behandeln

## Detection

- Total rules: 2
- Languages: javascript, typescript, python

## Rules by Language

### Javascript (1 rules)

- **HTTP Parameter Pollution Prevention in Express.js** [LOW]: Detects missing HTTP Parameter Pollution (HPP) protection in Express.js applications.
  - Remediation: Option 1 - Add hpp middleware (recommended):
  npm install hpp
  const hpp = require('hpp');
  app.use(hpp());

Option 2 - Validate parameters manually:
  const value = Array.isArray(req.query.param)
    ? req.query.param[0]  // Take first value
    : req.query.param;

### Typescript (1 rules)

- **HTTP Parameter Pollution Prevention in Express.js** [LOW]: Detects missing HTTP Parameter Pollution (HPP) protection in Express.js applications.
  - Remediation: Option 1 - Add hpp middleware (recommended):
  npm install hpp
  const hpp = require('hpp');
  app.use(hpp());

Option 2 - Validate parameters manually:
  const value = Array.isArray(req.query.param)
    ? req.query.param[0]  // Take first value
    : req.query.param;

### Python (1 rules)

- **HTTP Parameter Pollution** [MEDIUM]: Detects handling of duplicate HTTP parameters without proper validation.
  - Remediation: Check for duplicate parameters and reject requests with unexpected multiples.

```python
if len(request.args.getlist('param')) > 1:
    return "Duplicate parameters not allowed", 400
```

Learn more: https://shoulder.dev/learn/python/cwe-235/parameter-pollution