Cors Wildcard in Dynamodb

CORS wildcard misconfigurations in DynamoDB often occur when developers use overly permissive CORS policies in their API Gateway or Lambda functions that interact with DynamoDB tables. The most common pattern is setting the Access-Control-Allow-Origin header to "*" without considering the security implications for data stored in DynamoDB.

In DynamoDB contexts, this vulnerability typically appears in:

• API Gateway Lambda authorizers that proxy requests to DynamoDB
• Serverless functions using the AWS SDK to query DynamoDB
• Web applications that expose DynamoDB data through REST endpoints

The attack surface expands significantly because DynamoDB stores sensitive data like user profiles, session tokens, and application state. When CORS is misconfigured, an attacker can craft malicious websites that make authenticated requests to your DynamoDB-backed API, potentially exposing:

• User data stored in DynamoDB tables
• API keys or credentials cached in application state
• Business logic that processes DynamoDB queries

Consider this vulnerable Lambda function pattern:

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

exports.handler = async (event) => {
  const response = {
    headers: {
      'Access-Control-Allow-Origin': '*',
      'Access-Control-Allow-Credentials': true
    }
  };

  const params = {
    TableName: 'Users',
    Key: { id: event.pathParameters.id }
  };

  try {
    const data = await dynamodb.get(params).promise();
    response.statusCode = 200;
    response.body = JSON.stringify(data.Item);
  } catch (err) {
    response.statusCode = 500;
    response.body = JSON.stringify({ error: err.message });
  }

  return response;
};

This code allows any website to make credentialed requests to your DynamoDB API, potentially exposing user data stored in the 'Users' table. The combination of wildcard CORS with credentialed requests creates a perfect storm for data exfiltration.

Detecting CORS wildcard issues in DynamoDB environments requires examining both the API layer and the data access patterns. middleBrick's DynamoDB-specific scanning looks for several key indicators:

middleBrick's scanning approach for DynamoDB APIs includes:

middlebrick scan https://api.example.com/dynamodb/users/{id} 
  --profile dynamodb 
  --test-cors 
  --check-credentials

The scanner tests for CORS misconfigurations by:

1. Sending preflight OPTIONS requests with various Origin headers
2. Attempting credentialed requests from different domains
3. Analyzing DynamoDB query patterns in the response data
4. Checking for sensitive data exposure in error messages

Additional detection considerations for DynamoDB:

• Global secondary indexes that might expose unintended data
• Partition key enumeration through timing attacks
• Conditional writes that reveal data existence

Manual detection steps include:

# Check API Gateway CORS settings
aws apigateway get-rest-api --rest-api-id <id> --query 'cors'

Look for patterns like:

• Access-Control-Allow-Origin: *
• Access-Control-Allow-Credentials: true (with wildcard origin)
• Missing or overly permissive Access-Control-Allow-Methods

Fixing CORS wildcard issues in DynamoDB environments requires a multi-layered approach. The most effective remediation combines proper CORS configuration with DynamoDB-specific security controls.

First, implement strict CORS policies in your API Gateway or Lambda functions:

// Secure CORS configuration for DynamoDB API
const secureCors = {
  'Access-Control-Allow-Origin': 'https://yourdomain.com',
  'Access-Control-Allow-Methods': 'GET, POST, PUT, DELETE, OPTIONS',
 'Access-Control-Allow-Headers': 'Content-Type, Authorization',
  'Access-Control-Max-Age': '86400'
};

exports.handler = async (event) => {
  const origin = event.headers.origin;
  const allowedOrigins = ['https://yourdomain.com', 'https://app.yourdomain.com'];
  
  if (!allowedOrigins.includes(origin)) {
    return corsErrorResponse('Origin not allowed');
  }

  const response = {
    headers: {
      ...secureCors,
      'Access-Control-Allow-Origin': origin
    }
  };

  // DynamoDB query with proper authorization
  const params = {
    TableName: 'Users',
    Key: { id: event.pathParameters.id },
    ConditionExpression: 'attribute_exists(id) AND #owner = :owner',
    ExpressionAttributeNames: { '#owner': 'ownerId' },
    ExpressionAttributeValues: { ':owner': event.requestContext.authorizer.userId }
  };

  try {
    const data = await dynamodb.get(params).promise();
    response.statusCode = 200;
    response.body = JSON.stringify(data.Item);
  } catch (err) {
    response.statusCode = 403;
    response.body = JSON.stringify({ error: 'Access denied' });
  }

  return response;
};

Additional DynamoDB-specific security measures:

1. Attribute-level encryption - Use DynamoDB's native encryption for sensitive fields

// Encrypt sensitive data before storing in DynamoDB
const encryptedData = encryptUserData(userData);
await dynamodb.put({
  TableName: 'Users',
  Item: { id: userId, data: encryptedData }
});

2. Fine-grained access control - Use IAM policies with condition statements

// IAM policy for DynamoDB access
{