Type Confusion on Aws

Type confusion in Aws applications typically occurs when dynamic data structures are deserialized without strict type validation. In Node.js environments, which power many Aws Lambda functions and APIs, this vulnerability can lead to arbitrary code execution or data corruption.

A common manifestation involves JSON deserialization where an attacker manipulates the input to change the expected data type. Consider an Aws Lambda function handling API Gateway requests:

const { APIGatewayProxyEvent } = require('aws-lambda');

exports.handler = async (event) => {
  const body = JSON.parse(event.body);
  
  // Type confusion vulnerability
  if (body.userId === 'admin') {
    return accessAdminPanel();
  }
  
  return { statusCode: 200, body: 'Access granted' };
};

The vulnerability here is that body.userId is compared as a string, but if an attacker sends userId as an array or object, JavaScript's loose equality comparison can produce unexpected results.

Another Aws-specific scenario involves DynamoDB operations where type confusion can lead to NoSQL injection:

const AWS = require('aws-sdk');
const dynamodb = new AWS.DynamoDB.DocumentClient();

exports.handler = async (event) => {
  const params = {
    TableName: 'users',
    Key: {
      id: event.pathParameters.id // Type confusion here
    }
  };
  
  const result = await dynamodb.get(params).promise();
  return result.Item;
};

If event.pathParameters.id is expected to be a string but receives a number or object, it can bypass authorization checks or access unintended data.

Detecting type confusion in Aws environments requires both static analysis and runtime monitoring. For Lambda functions and API Gateway endpoints, middleBrick's black-box scanning approach is particularly effective because it tests the actual runtime behavior without requiring source code access.

middleBrick's scanning process for Aws APIs includes:

• Authentication bypass testing with various data types
• Parameter type manipulation to trigger unexpected code paths
• Schema validation against OpenAPI specifications
• Runtime type checking in Lambda function invocations

The scanner specifically tests for Aws patterns like:

// What middleBrick actively tests for
const maliciousPayloads = [
  { userId: ['admin'] },           // Array instead of string
  { userId: { admin: true } },     // Object instead of string
  { userId: 0 },                   // Number instead of string
  { userId: null },                // Null instead of string
  { userId: '' },                  // Empty string edge case
];

For Aws-native detection, CloudWatch Logs can be configured to flag suspicious type conversions:

const { isString, isNumber, isObject } = require('lodash');

exports.handler = async (event) => {
  const body = JSON.parse(event.body);
  
  // Runtime type validation
  if (!isString(body.userId)) {
    console.warn('Type confusion attempt detected:', typeof body.userId);
    return { statusCode: 400, body: 'Invalid input type' };
  }
  
  // Continue with validated logic
};

middleBrick's OpenAPI analysis also cross-references parameter definitions with actual runtime behavior, flagging mismatches between documented and implemented types.

Remediating type confusion in Aws applications requires strict input validation and type enforcement. The Aws ecosystem provides several native approaches for securing your APIs.

For API Gateway endpoints, use request validation schemas:

{
  "type": "object",
  "properties": {
    "userId": {
      "type": "string",
      "minLength": 1
    }
  },
  "required": ["userId"]
}

This JSON schema can be attached to your API Gateway method to reject invalid types before they reach your Lambda function.

In Lambda functions, implement strict type checking:

const { APIGatewayProxyEvent } = require('aws-lambda');

function validateUserId(userId) {
  if (typeof userId !== 'string' || userId.trim() === '') {
    throw new Error('Invalid userId type');
  }
  return userId;
}

exports.handler = async (event) => {
  try {
    const body = JSON.parse(event.body);
    const validatedUserId = validateUserId(body.userId);
    
    // Safe to use validatedUserId
    if (validatedUserId === 'admin') {
      return accessAdminPanel();
    }
    
    return { statusCode: 200, body: 'Access granted' };
  } catch (error) {
    return { 
      statusCode: 400, 
      body: 'Invalid request: ' + error.message 
    };
  }
};

For DynamoDB operations, use explicit type casting:

const AWS = require('aws-sdk');
const dynamodb = new AWS.DynamoDB.DocumentClient();

function validateIdParam(id) {
  if (typeof id !== 'string') {
    throw new Error('ID must be a string');
  }
  return id;
}

exports.handler = async (event) => {
  try {
    const id = validateIdParam(event.pathParameters.id);
    
    const params = {
      TableName: 'users',
      Key: { id }
    };
    
    const result = await dynamodb.get(params).promise();
    return result.Item;
  } catch (error) {
    return { statusCode: 400, body: error.message };
  }
};

middleBrick's remediation guidance includes these specific patterns and provides severity-based recommendations for your Aws applications.