# 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')
        capabilities = device_config.get('capabilities', [])
        telemetry_interval = device_config.get('telemetry_interval', 60)
        registry_entry = {
            'id': device_id,
            'firmware': firmware_ver,
            'features': capabilities,
            'interval': telemetry_interval,
            'status': 'provisioned'
        }
        return jsonify({'success': True, 'device': registry_entry}), 200
    except Exception as e:
        return jsonify({'success': False, 'error': str(e)}), 400
```

## Explanation

The application uses yaml.load() with yaml.Loader to deserialize untrusted YAML data from HTTP POST requests. This allows attackers to execute arbitrary Python code by crafting malicious YAML payloads that exploit Python's object serialization features, leading to Remote Code Execution (RCE).

## Remediation

The fix replaces yaml.load() with yaml.safe_load(), which only deserializes standard YAML tags (strings, numbers, lists, dicts) and does not allow arbitrary Python object instantiation. Additionally, a type check ensures the parsed result is a dictionary before accessing keys, preventing unexpected behavior from non-mapping YAML inputs.

## 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({'success': False, 'error': 'Invalid manifest format'}), 400
        device_id = device_config.get('device_id', 'unknown')
        firmware_ver = device_config.get('firmware_version', '1.0.0')
        capabilities = device_config.get('capabilities', [])
        telemetry_interval = device_config.get('telemetry_interval', 60)
        registry_entry = {
            'id': device_id,
            'firmware': firmware_ver,
            'features': capabilities,
            'interval': telemetry_interval,
            'status': 'provisioned'
        }
        return jsonify({'success': True, 'device': registry_entry}), 200
    except Exception as e:
        return jsonify({'success': False, 'error': str(e)}), 400
```