Arp Spoofing in Dynamodb

ARP spoofing is a layer-2 network attack where an attacker sends falsified ARP messages onto a local area network, linking their MAC address with the IP address of a legitimate server (like a gateway or API endpoint). This enables a man-in-the-middle (MITM) position to intercept, modify, or redirect traffic. While DynamoDB itself is a fully-managed AWS service whose internal network is not accessible to customers, the vulnerability manifests at the application layer when code running on a compromised host (e.g., an EC2 instance, on-prem server, or developer laptop) communicates with DynamoDB over an insecure channel.

The attack chain typically follows this pattern:

1. Initial Compromise: The attacker gains access to a machine on the same broadcast domain as the application server (e.g., via malware, phishing, or exploiting a local service).
2. ARP Spoofing/Poisoning: Using tools like arpspoof or bettercap, the attacker poisons the ARP cache of the target application server and the local gateway, positioning themselves between the two.
3. Traffic Interception: The application server's outbound traffic to DynamoDB (or any external endpoint) is now routed through the attacker's machine. If the application uses unencrypted HTTP or fails to properly validate TLS certificates, the attacker can read or alter the DynamoDB API requests and responses.
4. Credential/Data Harvesting: The attacker captures AWS access keys (if hard-coded or exposed in memory), session tokens, or raw DynamoDB items (including PII) from the intercepted traffic.

This is not a vulnerability in DynamoDB itself, but in the client application's network security practices. A common misconfiguration is using the DynamoDB Document Client or AWS SDK with HTTP instead of HTTPS, or disabling certificate validation for convenience in development. For example, the following Node.js code creates a vulnerable client:

const { DynamoDBClient } = require('@aws-sdk/client-dynamodb');

// VULNERABLE: Using HTTP endpoint and disabling TLS validation
const client = new DynamoDBClient({
  region: 'us-east-1',
  endpoint: 'http://dynamodb.us-east-1.amazonaws.com', // Note http://
  tls: false // Disables certificate validation
});

If this code runs on a network where ARP spoofing is occurring, all DynamoDB operations (GetItem, PutItem, Query) are transmitted in plaintext, exposing both data and credentials.

middleBrick detects this class of vulnerability by analyzing the API endpoint's runtime behavior and configuration. The scanner does not inspect your source code but probes the live endpoint to check for insecure transport and authentication practices that would enable MITM attacks. Relevant security checks from middleBrick's suite include:

• Encryption: Verifies that all API requests to DynamoDB use TLS 1.2+ and that the server certificate is properly validated.
• Data Exposure: Checks if sensitive data (PII, API keys) is transmitted in clear text or weakly encrypted.
• Authentication: Assesses whether credentials are sent over insecure channels or lack proper signing (SigV4).

When scanning an API that proxies DynamoDB operations (e.g., a custom REST wrapper around DynamoDB), middleBrick will test for:

A typical middleBrick report for this issue might show a High severity finding in the Encryption category, with a proof-of-concept curl command demonstrating an HTTP request that returns a 200 OK and sensitive data. The scanner's OpenAPI/Swagger analysis also cross-references the spec: if the API defines schemes: [http] or lacks securitySchemes for AWS SigV4, it flags the design-time risk.

For LLM/AI-powered APIs that use DynamoDB as a backend, middleBrick extends its checks to include LLM/AI Security probes that might indirectly expose DynamoDB data via prompt injection, though this is a separate attack vector from ARP spoofing.

Remediation focuses on defense-in-depth: encrypting all traffic, using short-lived credentials, and restricting network egress. The following code examples demonstrate secure patterns for Node.js (AWS SDK v3) and Python (Boto3).

1. Enforce HTTPS and Validate TLS Certificates

Always use the default https:// endpoint and ensure TLS validation is enabled. The AWS SDKs do this by default, but configurations can accidentally disable it.

// SECURE: Explicitly set endpoint to HTTPS and keep tls: true (default)
const { DynamoDBClient } = require('@aws-sdk/client-dynamodb');

const client = new DynamoDBClient({
  region: 'us-east-1',
  endpoint: 'https://dynamodb.us-east-1.amazonaws.com', // Must be https://
  tls: true // Default, but be explicit in security-critical code
});

// Example secure operation
const command = new GetItemCommand({
  TableName: 'Users',
  Key: { userId: { S: '123' } }
});
const response = await client.send(command);

What to avoid: Never set tls: false or use http:// endpoints, even in development. Use environment-specific configuration that enforces TLS in all non-localhost environments.

2. Use IAM Roles Instead of Long-Term Credentials

Hard-coding accessKeyId and secretAccessKey in application code risks exposure via memory dumps or logs. Use IAM roles attached to the compute resource (EC2 instance role, ECS task role, Lambda execution role). The SDK automatically retrieves temporary credentials from the metadata service.

// SECURE: No credentials in code - SDK uses instance role
const client = new DynamoDBClient({ region: 'us-east-1' });

// If you must use explicit credentials (e.g., on-prem), source them from
// environment variables or AWS Secrets Manager, never from source code.
const client = new DynamoDBClient({
  region: 'us-east-1',
  credentials: {
    accessKeyId: process.env.AWS_ACCESS_KEY_ID!, // From env
    secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY!
  }
});

3. Restrict Network Egress with VPC Endpoints

Deploy your application in a VPC and use a DynamoDB VPC Gateway Endpoint. This keeps traffic between your VPC and DynamoDB within the AWS network, never traversing the public internet. This mitigates the impact of ARP spoofing on the local network because the traffic never leaves the controlled VPC.

// Terraform example to create a DynamoDB Gateway Endpoint
resource "aws_vpc_endpoint" "dynamodb" {
  vpc_id       = aws_vpc.main.id
  service_name = "com.amazonaws.us-east-1.dynamodb"
  route_table_ids = [aws_route_table.main.id]
}

With this endpoint, your application's DynamoDB traffic uses private IP addresses and AWS's internal network. Even if an attacker performs ARP spoofing on the local host, they cannot intercept traffic that never goes through the local gateway.

4. Enable Encryption at Rest and in Transit (AWS-Managed)

While this is a console/API configuration, ensure your DynamoDB table has Server-Side Encryption enabled with an AWS-managed key (or your own KMS key). This is a last line of defense if data is exfiltrated via MITM.

// AWS CLI to enable encryption on a table
aws dynamodb update-table \
  --table-name Users \
  --sse-specification Enabled=true,SSEType=KMS

Combine these with network-level controls: use security groups to restrict outbound traffic to only the DynamoDB VPC endpoint IPs, and implement AWS WAF or network ACLs for additional layers.

Q: Can ARP spoofing directly attack DynamoDB's infrastructure?
A: No. DynamoDB is a managed AWS service whose underlying network is not accessible to customers. The attack targets the client application's network path to DynamoDB. If the application runs on a compromised host and uses unencrypted connections, an attacker on the same local network can intercept that traffic.

Q: Does middleBrick scan my DynamoDB tables directly?
A: No. middleBrick scans your API endpoints (the HTTP/HTTPS interfaces your application exposes). It does not connect to AWS services like DynamoDB directly. The scanner tests how your API handles requests and whether it securely communicates with backend services like DynamoDB. For DynamoDB-specific risks, you would scan the API that acts as a proxy or gateway to your database.