Dns Cache Poisoning in Echo Go with Dynamodb

DNS cache poisoning can arise in an Echo Go service that uses DynamoDB when the application resolves external hostnames at runtime and uses the results to form database requests or endpoint connections. For example, if the service calls a third-party hostname to build a DynamoDB endpoint or to construct an API URL, and the hostname is resolved each time without validation, an attacker who can poison the local resolver cache may redirect the client to a malicious host. This can cause the service to issue DynamoDB operations to an unintended endpoint, potentially bypassing network-level segregation or feeding the service malicious input that affects data stored in DynamoDB.

Echo Go does not provide built-in DNS caching; it relies on the standard Go net resolver, which uses the operating system cache. If your deployment environment has a vulnerable resolver or you rely on external DNS-based service discovery, poisoned cache entries can lead the Go net/http client (used by Echo) to connect to attacker-controlled IPs. When those IPs present themselves as legitimate DynamoDB-compatible endpoints or when they return crafted responses, the application may trust and persist attacker-influenced data into DynamoDB tables. This is especially relevant if your code dynamically constructs table names, keys, or conditional expressions from values derived from network calls, because unchecked input can directly affect DynamoDB request parameters and expose operations like GetItem, PutItem, or Query to unintended data paths.

An example pattern is resolving a "table host" via DNS and using the result to compute request endpoints or to select logical partitions in DynamoDB. In such flows, an Echo route handler that performs DNS lookups on each request and then builds a DynamoDB client configuration with the resolved address can be tricked into directing traffic to a rogue server. If the handler then forwards client-controlled data into DynamoDB based on the poisoned context, the attack surface expands to include data integrity issues, injection-like behavior against the logical partitioning scheme, and potential exposure of credentials or tokens that are embedded in the request flow. Because middleBrick tests unauthenticated scenarios, such misconfigurations can be detected as part of the SSRF and Input Validation checks, highlighting how untrusted external resolution can reach backend data stores.

To reduce risk, avoid dynamic DNS-based resolution for critical endpoints and instead use static, validated configuration for DynamoDB service addresses. If you must use dynamic discovery, validate and restrict resolved values against an allowlist and perform resolution at startup rather than per request. In Echo Go, you can initialize the AWS SDK with a custom endpoint resolver that is populated from a secure source, and you can sanitize all inputs that influence table or key construction before issuing DynamoDB operations.

Below is a concrete example in Go using the AWS SDK for Go v2. It shows how to configure a DynamoDB client with a fixed endpoint and how to safely construct request parameters without relying on runtime DNS lookups. The code avoids concatenating raw strings to form table names and uses explicit constants or validated mappings instead.

// main.go
package main

import (
	"context"
	"fmt"
	"net/http"

	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb/types"
	"github.com/labstack/echo/v4"
)

// safeTableMap ensures only known tables are allowed.
var safeTableMap = map[string]string{
	"users": "myapp-users",
	"logs":  "myapp-logs",
}

func getAllowedTable(name string) (string, bool) {
	t, ok := safeTableMap[name]
	return t, ok
}

func main() {
	// Use a fixed endpoint; avoid runtime DNS-based endpoint selection.
	cfg, err := config.LoadDefaultConfig(context.TODO(),
		config.WithEndpointResolverWithOptions(aws.EndpointResolverWithOptionsFunc(
			func(service, region string, options ...interface{}) (aws.Endpoint, error) {
				// Static endpoint; replace with your region-specific endpoint if needed.
				return aws.Endpoint{URL: "https://dynamodb.us-east-1.amazonaws.com"}, nil
			}),
		),
	)
	if err != nil {
		http.Error(nil, "unable to load SDK config", http.StatusInternalServerError)
		return
	}

	client := dynamodb.NewFromConfig(cfg)
	e := echo.New()

	e.GET("/user/:id", func(c echo.Context) error {
		id := c.Param("id")
		if id == "" {
			return c.String(http.StatusBadRequest, "missing id")
		}

		table, ok := getAllowedTable("users")
		if !ok {
			return c.String(http.StatusBadRequest, "invalid table request")
		}

		out, err := client.GetItem(c.Request().Context(), &dynamodb.GetItemInput{
			TableName: aws.String(table),
			Key: map[string]types.AttributeValue{
				"user_id": &types.AttributeValueMemberS{Value: id},
			},
		})
		if err != nil {
			return c.String(http.StatusInternalServerError, "unable to fetch user")
		}

		if out.Item == nil {\n			return c.String(http.StatusNotFound, "user not found")
		}

		// Process out.Item safely; avoid reflecting raw values into executable formats.
		return c.JSON(http.StatusOK, out.Item)
	})

	// Start server on a controlled port with validated routes.
	if err := e.Start(":8080"); err != nil {
		// handle error
	}
}

Additionally, apply input validation on all user-controlled fields used in DynamoDB expressions, and avoid passing raw query parameters into ConditionExpression or ExpressionAttributeValues without strict type checks. Prefer parameterized expressions and deny-list validation for attribute names to prevent injection-like manipulation of logical partitions. These practices reduce the impact of any DNS-level compromise by ensuring that even if an attacker redirects network traffic, the application will not accept unsafe table or key values.