Arp Spoofing in Hanami with Dynamodb

Arp spoofing is a Layer 2 attack where an adversary sends falsified ARP responses to associate their MAC address with the IP of a legitimate host, such as your Hanami application server or its DynamoDB gateway. In a typical Hanami service that communicates with Amazon DynamoDB over the network, an attacker on the same subnet (e.g., within a cloud VPC or shared host environment) can perform ARP spoofing to intercept or modify traffic intended for DynamoDB endpoints. This does not exploit DynamoDB itself, because DynamoDB operates over HTTPS and requires valid credentials, but it compromises the confidentiality and integrity of the communication path between Hanami and DynamoDB.

When Hanami resolves a DynamoDB endpoint (e.g., dynamodb.us-east-1.amazonaws.com) and sends requests signed with AWS credentials, an attacker who successfully spoofs ARP can observe or manipulate unencrypted metadata in transit, potentially capturing sensitive constructs like IAM role associations or temporary tokens if TLS is improperly validated. The exposure is heightened if Hanami resolves hostnames once and caches them, allowing the spoofed mapping to persist across requests. Because DynamoDB traffic relies on correct routing through the network stack, ARP spoofing can redirect requests to a malicious host that terminates TLS and relays to the real DynamoDB, enabling credential theft or request tampering if certificate validation is weak.

In cloud environments, the attack surface for ARP spoofing is typically limited to the local network segment, but misconfigured VPC peering, security groups, or shared tenancy can extend exposure. Hanami applications that do not enforce strict hostname verification or rely on outdated DNS/caching behavior are more susceptible to this indirect risk. Because DynamoDB requires signed requests, intercepted requests alone are not sufficient to mutate data, but combined with other weaknesses (e.g., credential leakage via logs or SSRF), ARP spoofing can be a stepping stone in a broader attack chain.

Defenses focus on ensuring Hanami validates endpoints and credentials robustly when communicating with DynamoDB. Use HTTPS with strict certificate validation, avoid hostname caching that can be poisoned, and apply network-level hardening to limit ARP spoofing impact. Below are concrete practices and code examples for a Hanami service that interacts with DynamoDB using the official AWS SDK for Ruby.

1. Enforce TLS and strict hostname verification

Ensure your HTTP client used by the AWS SDK verifies TLS certificates and does not disable peer verification. Configure the SDK with a custom HTTP client if needed, and avoid global overrides that weaken validation.

# config/initializers/dynamodb.rb
require 'aws-sdk-dynamodb'

# Use default AWS credential chain with explicit region
client = Aws::DynamoDB::Client.new(
  region: 'us-east-1',
  # Ensure HTTPS is used (default); do not set `:ssl_handler` to an insecure custom handler
  http_wire_trace: false # keep tracing disabled in production unless needed
)

# Example safe query with explicit table name and condition expression
resp = client.get_item({
  table_name: 'UserProfiles',
  key: { 'user_id' => { s: 'u-12345' } },
  projection_expression: 'user_id, email, created_at'
})
puts resp.item

2. Isolate DynamoDB traffic via VPC endpoints

In cloud deployments, use VPC endpoints for DynamoDB to keep traffic off the public internet and reduce exposure to Layer 2 attacks. This ensures that even if ARP spoofing occurs within the subnet, the traffic path is constrained. Combine this with security groups that limit source ranges.

3. Validate and pin endpoints in Hanami routing and service objects

When constructing URLs or hostnames for service clients, validate against an allowlist and avoid dynamic host resolution based on user input. Explicitly set the endpoint to the expected AWS regional endpoint.

# app/services/dynamodb_service.rb
class DynamoDbService
  ENDPOINT = 'dynamodb.us-east-1.amazonaws.com'

  def initialize
    @client = Aws::DynamoDB::Client.new(
      region: 'us-east-1',
      endpoint: "https://#{ENDPOINT}",
      # Use AWS SigV4; do not disable signing
    )
  end

  def find_user(user_id)
    @client.get_item(
      table_name: 'UserProfiles',
      key: { 'user_id' => { s: user_id } }
    )
  end
end

4. Apply network-level protections

Configure the host firewall to restrict unnecessary ARP responses and consider using static ARP entries for critical internal endpoints if the environment permits. In Hanami deployments, ensure that the underlying infrastructure follows cloud provider best practices for VPC and subnet ACLs to minimize the risk of ARP spoofing.