# 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: Medium 2 languages covered
- Impact: Medium Review recommended
- Prevention: Documented 2 fix examples

**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

Prevention strategies for Improper Handling of Extra Parameters based on 2 Shoulder detection rules.

### Node.js

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

- Bypass Protection Mechanism
- Modify Application Data

## Mitigations

- Define and enforce a policy for handling duplicate parameters
- Reject requests with duplicate security-sensitive parameters
- Use frameworks that handle duplicates consistently

## 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