# 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.

**Stack:** JavaScript

- Prevalence: 中 2 言語をカバー
- Impact: ミディアム レビュー推奨
- Prevention: 文書化済み 2 件の修正例

**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

1 件の Shoulder 検出ルールに基づく Improper Handling of Extra Parameters の予防策。

### JavaScript

Add hpp middleware to normalize duplicate query parameters

## Warning Signs

- [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

- 保護メカニズムの回避
- アプリケーションデータの変更

## Mitigations

- 重複したパラメータを扱うためのポリシーを定義し、適用する
- セキュリティに敏感なパラメータが重複しているリクエストは拒否する
- 重複を一貫して扱うフレームワークを使用する

## 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;