Dns Rebinding in Echo Go with Dynamodb

DNS rebinding is a network-based attack that manipulates DNS responses to make a victim’s browser believe a remote host is reachable at an internal IP address. When an Echo Go service that interacts with DynamoDB is exposed to untrusted network paths—such as the public internet without strict origin validation—the service can be tricked into making backend requests to internal AWS endpoints that would otherwise be unreachable.

In this scenario, an attacker registers a domain and hosts malicious JavaScript on a compromised or rogue server. The DNS records for that domain are configured with a low TTL and are repeatedly switched between an attacker-controlled public IP and a target internal address (for example, an internal DynamoDB endpoint or an internal load balancer serving metadata). When a user visits the attacker’s page, their browser is induced to make requests that traverse the internal network, potentially reaching the DynamoDB service or internal services that accept requests on behalf of the application.

If the Echo Go application accepts requests from the browser or from external callers without validating the intended destination, an HTTP-triggered handler may forward data to a resolved endpoint that maps to an internal AWS resource. While the attack targets the network layer, the presence of DynamoDB as a backend datastore increases the impact: sensitive data or write operations could be relayed through the rebind, leading to unauthorized data access or injection of malicious items into DynamoDB tables.

Echo Go applications that construct AWS SDK clients dynamically, use shared HTTP clients, or do not enforce strict endpoint policies may inadvertently route requests to internal IPs discovered through rebinding. The vulnerability is not in DNS or in DynamoDB itself, but in the application’s relaxed destination validation and the broad reach of the network path between the client, the Echo Go service, and AWS infrastructure.

middleBrick can detect this class of risk by scanning the unauthenticated attack surface of the Echo Go service. It runs checks for SSRF and related network-induced routing issues and flags findings that could allow unintended internal access, including paths that involve DynamoDB endpoints. By correlating runtime behavior with the OpenAPI specification and resolving $ref definitions, the scanner identifies mismatches between expected and observed endpoint destinations.

To mitigate DNS rebinding risks in an Echo Go application that uses DynamoDB, focus on strict endpoint validation, avoiding dynamic resolution of AWS service endpoints, and ensuring that outbound requests are constrained to known AWS regions and endpoints.

First, configure the AWS SDK for Go to use a fixed endpoint resolver that does not rely on external DNS resolution for sensitive operations. This prevents the SDK from following manipulated DNS responses that could redirect requests internally.

package main

import (
	"context"
	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/feature/dynamodb/attributevalue"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
	"github.com/labstack/echo/v4"
	"net"
)

// fixedResolver returns a custom endpoint resolver that only allows specific regional endpoints.
type fixedResolver struct{}

func (r *fixedResolver) EndpointFor(service, region string, options ...func(*aws.EndpointOptions)) (aws.Endpoint, error) {
	// Restrict to known, expected endpoints; reject any non-standard hostnames.
	if service == "dynamodb" && region == "us-east-1" {
		return aws.Endpoint{
			URL:               "https://dynamodb.us-east-1.amazonaws.com",
			SigningRegion:     region,
			HostnameImmutable: true,
		}, nil
	}
	if service == "dynamodb" && region == "us-west-2" {
		return aws.Endpoint{
			URL:               "https://dynamodb.us-west-2.amazonaws.com",
			SigningRegion:     region,
			HostnameImmutable: true,
		}, nil
	}
	return aws.Endpoint{}, aws.NewEndpointNotFoundError(service, region)
}

func main() {
	e := echo.New()

	cfg, err := config.LoadDefaultConfig(context.TODO(),
		config.WithEndpointResolver(fixedResolver{}),
		config.WithRegion("us-east-1"),
	)
	if err != nil {
		panic("failed to load SDK config")
	}

	client := dynamodb.NewFromConfig(cfg)

	e.GET("/items/:id", func(c echo.Context) error {
		id := c.Param("id")
		out, err := client.GetItem(c.Request().Context(), &dynamodb.GetItemInput{
			TableName: aws.String("ItemsTable"),
			Key: map[string]types.AttributeValue{
				"ID": &types.AttributeValueMemberS{Value: id},
			},
		})
		if err != nil {
			return c.String(500, "failed to get item")
		}

		var item map[string]string
		err = attributevalue.UnmarshalMap(out.Item, &item)
		if err != nil {
			return c.String(500, "failed to unmarshal item")
		}

		return c.JSON(200, item)
	})

	// Bind to a specific interface to avoid unintended exposure.
	if err := e.Start(net.JoinHostPort("0.0.0.0", "8080")); err != nil {
		panic(err)
	}
}

Second, enforce network-level constraints by binding the HTTP server to a specific interface and by using firewall rules that prevent the process from reaching internal AWS metadata services. In containerized environments, avoid host network mode and use service mesh policies to restrict egress to known AWS endpoints only.

Third, validate and sanitize all inputs used to construct requests or query parameters that influence routing. Echo Go middleware can reject suspicious Host headers and ensure that requests originate from expected sources before interacting with DynamoDB clients.

Finally, use the middleBrick CLI to scan the Echo Go endpoint and verify that no SSRF or DNS rebinding vectors remain. The scanner’s checks for SSRF and unsafe consumption will highlight risky patterns, allowing developers to harden the service before deployment.