Zone Transfer in Hanami with Hmac Signatures

In a Hanami application, a zone transfer vulnerability can occur when internal DNS records are exposed through an endpoint that does not properly validate the origin or integrity of requests. When Hmac Signatures are used for request authentication but are implemented inconsistently—such as using a static key, failing to include critical request attributes in the signature, or not validating the signature on the server side—an attacker who can observe or forge requests may be able to replay or manipulate them to trigger a zone transfer.

For example, if an endpoint that returns DNS zone data uses an Hmac Signature derived only from the request body without including the request path or a nonce, an attacker can intercept a valid signed request and replay it to the same endpoint. If the endpoint lacks strict access controls and rate limiting, this replay can be used to repeatedly query internal DNS servers, potentially leaking zone transfers that should never be exposed externally. This becomes especially risky when the application trusts client-supplied identifiers (such as a domain name parameter) and uses them directly in DNS queries without validation.

Additionally, if the Hmac Signatures are computed using a shared secret stored in configuration without rotation, and the same secret is used across multiple endpoints or services, a compromised secret enables an attacker to forge authenticated requests across the system. In the context of zone transfer, this means an attacker could craft a signed request that causes the Hanami app to query an internal DNS server and return zone data, effectively bypassing network segmentation controls that rely on the assumption that DNS queries originate only from trusted internal services.

Because middleBrick scans the unauthenticated attack surface and runs checks such as Input Validation and BOLA/IDOR in parallel, it can detect endpoints that expose sensitive data without requiring authentication. Findings related to weak or inconsistent Hmac usage—such as missing scope in the signed payload—will appear in the scan results with severity and remediation guidance, helping teams identify where Hmac Signatures are not providing the intended integrity guarantees.

To remediate zone transfer risks linked to Hmac Signatures in Hanami, ensure the signature covers all components that affect request processing, including the HTTP method, request path, selected headers, and a server-side nonce or timestamp. Never derive the Hmac using only the body or only user-controlled parameters. Validate the signature on the server before performing any DNS-related operations, and enforce strict allowlists for domains and record types.

Use a consistent, server-generated nonce or timestamp included in both the request and the signature to prevent replay attacks. Rotate the Hmac secret regularly and avoid sharing the same secret across unrelated services. Combine Hmac verification with other controls such as strict network policies and rate limiting to reduce the impact of any misconfiguration.

Example of a secure Hmac signature generation in Ruby for Hanami (client-side):

require 'openssl'require 'base64'
secret = ENV['HMAC_SECRET']timestamp = Time.now.utc.iso8601path = '/api/v1/dns/query'body = { domain: 'example.com', type: 'AXFR' }.to_jsonmessage = "#{timestamp}\n#{path}\n#{body}"signature = OpenSSL::HMAC.hexdigest('sha256', secret, message)
headers = {
  'X-API-Timestamp' => timestamp,
  'X-API-Signature' => signature,
  'Content-Type' => 'application/json'
}

Example of secure Hmac signature verification in Hanami (server-side):

class VerifyHmac
  def initialize(app)
    @app = app
  end

  def call(ctx)
    timestamp = ctx.request.headers['X-API-Timestamp']
    received_signature = ctx.request.headers['X-API-Signature']
    return [401, { 'Content-Type' => 'application/json' }, [{ error: 'missing_timestamp' }.to_json]] unless timestamp
    return [401, { 'Content-Type' => 'application/json' }, [{ error: 'missing_signature' }.to_json]] unless received_signature

    # Reject stale requests (e.g., >2 minutes old)
    request_time = Time.iso8601(timestamp)rescue nil    return [400, { 'Content-Type' => 'application/json' }, [{ error: 'invalid_timestamp' }.to_json]] unless request_time    return [400, { 'Content-Type' => 'application/json' }, [{ error: 'stale_request' }.to_json]] if (Time.now - request_time) > 120

    path = ctx.env['REQUEST_PATH']
    body = ctx.request.body.read
    ctx.request.body.rewind

    secret = ENV['HMAC_SECRET']
    message = "#{timestamp}\n#{path}\n#{body}"
    expected_signature = OpenSSL::HMAC.hexdigest('sha256', secret, message)

    unless secure_compare(expected_signature, received_signature)
      return [401, { 'Content-Type' => 'application/json' }, [{ error: 'invalid_signature' }.to_json]]
    end

    @app.call(ctx)
  end

  private

  def secure_compare(a, b)
    return false unless a.bytesize == b.bytesize
    l = a.unpack 'H*'a_hex, b_hex = l[0], b.unpack('H*')[0]
    return false unless b_hex.size == a_hex.size
    result = 0
    a_hex.each_char.with_index { |c, i| result |= c.to_i(16) ^ b_hex[i].to_i(16) }
    result == 0
  end
end

# In your Hanami app configuration
use VerifyHmac

These examples include timestamp validation, path and body binding, and a constant-time comparison to mitigate timing attacks. By including the request path and a timestamp in the signed payload, you prevent attackers from replaying a signed request to a different endpoint or at a later time, which is critical when the endpoint can trigger zone transfer behavior.