# Unsafe YAML Deserialization via yaml.load()

Language: Python
Severity: Critical
CWE: CWE-502

## Source
8

## Flow
8-10

## Sink
10

## Vulnerable Code
```python
import yaml
from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route('/iot/device/provision', methods=['POST'])
def provision_iot_device():
    device_manifest = request.data.decode('utf-8')
    try:
        device_config = yaml.load(device_manifest, Loader=yaml.Loader)
        device_id = device_config.get('device_id', 'unknown')
        firmware_ver = device_config.get('firmware_version', '1.0.0')
        security_profile = device_config.get('security_profile', {})
        
        provisioning_result = {
            'status': 'provisioned',
            'device_id': device_id,
            'firmware': firmware_ver,
            'profile': security_profile
        }
        return jsonify(provisioning_result), 200
    except Exception as err:
        return jsonify({'error': 'Provisioning failed', 'details': str(err)}), 400
```

## Explanation

The application uses yaml.load() with yaml.Loader to deserialize untrusted YAML data received from HTTP POST requests. This allows attackers to execute arbitrary Python code by crafting malicious YAML payloads containing Python object constructor tags, leading to Remote Code Execution during the deserialization process.

## Remediation

The fix replaces yaml.load() with yaml.safe_load(), which only deserializes standard YAML tags (strings, numbers, lists, dicts) and refuses to construct arbitrary Python objects. This prevents Remote Code Execution via malicious YAML payloads containing Python object constructor tags. An additional type check ensures the parsed result is a dictionary before accessing its keys.

## Secure Code
```python
import yaml
from flask import Flask, request, jsonify

app = Flask(__name__)

@app.route('/iot/device/provision', methods=['POST'])
def provision_iot_device():
    device_manifest = request.data.decode('utf-8')
    try:
        device_config = yaml.safe_load(device_manifest)
        if not isinstance(device_config, dict):
            return jsonify({'error': 'Provisioning failed', 'details': 'Invalid manifest format'}), 400
        device_id = device_config.get('device_id', 'unknown')
        firmware_ver = device_config.get('firmware_version', '1.0.0')
        security_profile = device_config.get('security_profile', {})
        
        provisioning_result = {
            'status': 'provisioned',
            'device_id': device_id,
            'firmware': firmware_ver,
            'profile': security_profile
        }
        return jsonify(provisioning_result), 200
    except Exception as err:
        return jsonify({'error': 'Provisioning failed', 'details': str(err)}), 400
```