Zone Transfer in Fiber with Dynamodb

A zone transfer in the context of DNS refers to the replication of DNS zone data from a primary nameserver to secondary nameservers. When a service is built using Fiber and relies on Dynamodb for configuration or zone data storage, improper access controls can expose this replication mechanism. If the Dynamodb table storing DNS zone information is misconfigured, a remote attacker may trigger a zone transfer through the Fiber endpoint that queries the table, revealing internal hostnames, IP addresses, and infrastructure mapping.

The risk arises when Fiber routes directly expose administrative functionality (such as /transfer/zone) without authentication and with overly permissive Dynamodb permissions. Because middleBrick tests unauthenticated attack surfaces, it can detect whether a Fiber-hosted endpoint allows zone transfer-like queries that read sensitive DNS data from Dynamodb. Common missteps include using IAM roles that permit dynamodb:GetItem or dynamodb:Scan on zone-related tables from any network context, enabling an unauthenticated API caller to indirectly pull zone data by invoking the Fiber handler.

Specific patterns that heighten exposure include storing zone records as items with attributes like hostname, ip, and ttl, and implementing Fiber handlers that directly pass user-supplied parameters to Dynamodb queries without strict validation. If input validation is weak (another check run by middleBrick), an attacker can supply wildcard or enumeration inputs that cause the Dynamodb query to return large portions of the zone dataset. middleBrick’s checks for Input Validation, Authentication, and Data Exposure will flag cases where a Fiber endpoint returns DNS zone information without authorization, and will map findings to OWASP API Top 10 and relevant compliance frameworks.

To secure the interaction between Fiber and Dynamodb, apply strict input validation, scoped IAM permissions, and explicit query constraints. The following code examples illustrate secure patterns for querying zone data without enabling unintended transfers.

1. Use Parameterized Queries with Key Condition Expressions

Avoid passing raw user input into Dynamodb operations. Instead, use key condition expressions that reference a known partition key, such as a zone identifier, and validate the requester’s scope before execution.

const (
  zoneName = "example.com" // validated server-side, not from user input
)

func getZoneRecords(db *dynamodb.Client, zone string) ([]map[string]types.AttributeValue, error) {
  if zone == "" || !isValidZone(zone) {
    return nil, errors.New("invalid zone")
  }
  input := &dynamodb.QueryInput{
    TableName: aws.String("DNSZones"),
    KeyConditionExpression: aws.String("zone_name = :zone"),
    ExpressionAttributeValues: map[string]types.AttributeValue{
      ":zone": &types.AttributeValueMemberS{Value: zone},
    },
  }
  result, err := db.Query(context.TODO(), input)
  if err != nil {
    return nil, err
  }
  return result.Items, nil
}

2. Enforce Least-Privilege IAM Roles

Ensure the IAM role used by the Fiber service has only the permissions needed for the specific DynamoDB operations. Prefer dynamodb:GetItem over dynamodb:Scan, and scope the resource ARN to the specific table.

# Example IAM policy (conceptual; apply in AWS console or IaC)
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "dynamodb:GetItem"
      ],
      "Resource": "arn:aws:dynamodb:region:account-id:table/DNSZones"
    }
  ]
}

3. Validate and Sanitize Inputs in Fiber Handlers

Use strict regex-based validation for any user-supplied identifiers before using them in DynamoDB queries. This prevents wildcard or enumeration attacks that could lead to data exposure resembling a zone transfer.

func isValidZone(zone string) bool {
  pattern := `^[a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?(\.[a-zA-Z0-9]([a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?)*$`
  matched, _ := regexp.MatchString(pattern, zone)
  return matched
}

// Fiber route example
app.Get("/zone/:name", func(c *fiber.Ctx) error {
  zone := c.Params("name")
  if !isValidZone(zone) {
    return c.Status(fiber.StatusBadRequest).SendString("invalid zone")
  }
  records, err := getZoneRecords(db, zone)
  if err != nil {
    return c.Status(fiber.StatusInternalServerError).SendString("error")
  }
  return c.JSON(records)
})

4. Disable Administrative Endpoints in Production

Ensure that any endpoint capable of initiating replication or returning full zone data is not exposed publicly. middleBrick’s Authentication and BOLA checks will help identify routes that should be restricted.