Container Escape in Chi with Dynamodb

A container escape in a Chi application that uses DynamoDB typically occurs when an attacker who has achieved code execution inside a container can leverage DynamoDB client behavior or configuration to interact with the host runtime or other containers. Chi is a lightweight, composable router for Go, and while it does not directly interact with containers, an application using Chi can expose an unauthenticated or weakly authenticated API surface that permits unsafe DynamoDB operations, such as querying arbitrary tables or invoking DynamoDB Streams consumers that run with elevated permissions.

One realistic scenario: an endpoint built with Chi routes requests to a DynamoDB client with an IAM role attached to the container. If the endpoint lacks proper input validation (one of the 12 parallel checks), an attacker can supply a table name that references internal AWS resources, potentially triggering metadata service exposure via DynamoDB Streams or conditional writes that reach beyond intended boundaries. This becomes a container escape path when the compromised DynamoDB permissions allow the process to read instance metadata or communicate with the ECS task metadata endpoint, revealing credentials that enable lateral movement.

Another path involves misconfigured DynamoDB endpoints reachable from within the container. If the application does not enforce encryption or uses default AWS SDK behavior, an attacker might exploit SSRF (Server-Side Request Forgery) via DynamoDB client requests to probe internal AWS services or the container host itself. For example, a malicious request could target the EC2 instance metadata service (169.254.169.254) if the SDK is co-located in the same container and network namespaces are not properly restricted. The Chi router may inadvertently expose such endpoints if route handlers do not enforce strict parameter validation and least-privilege IAM policies.

Using middleBrick’s unauthenticated scan, such combinations are tested across the 12 security checks. Findings could highlight missing input validation, overly permissive BFLA (Business Function Level Authorization), or unsafe consumption patterns that allow an attacker to chain DynamoDB access with container-level operations. Remediation guidance provided by the scan will include tightening IAM roles, validating all DynamoDB table identifiers, and ensuring network policies isolate container traffic from metadata services.

Remediate container escape risks by applying strict input validation, least-privilege IAM, and safe DynamoDB client usage in Chi handlers. Below are concrete, working examples for Go using the aws-sdk-go-v2 library and Chi router.

1. Validate table names to prevent unauthorized resource access

Ensure that any user-supplied table name is checked against an allowlist or strict pattern before being passed to DynamoDB. This prevents attackers from targeting internal tables or metadata endpoints.

import (
	"context"
	"net/http"
	"regexp"

	"github.com/go-chi/chi/v5"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
)

func safeTableHandler(client *dynamodb.Client) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		tableName := chi.URLParam(r, "table")
		// Allow only alphanumeric and underscore, with a prefix
		matched, _ := regexp.MatchString(`^[a-zA-Z][a-zA-Z0-9_]{0,50}$`, tableName)
		if !matched {
			http.Error(w, "invalid table name", http.StatusBadRequest)
			return
		}
		// Proceed with safe table identifier
		_, err := client.DescribeTable(r.Context(), &dynamodb.DescribeTableInput{
			TableName: &tableName,
		})
		if err != nil {
			http.Error(w, "unable to describe table", http.StatusInternalServerError)
			return
		}
		w.Write([]byte("table validated"))
	}
}

2. Apply least-privilege IAM and disable unused SDK features

Configure the AWS SDK with a custom client that restricts DynamoDB operations to specific actions and resources. Avoid using wildcards in IAM policies attached to the container.

import (
	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/credentials/stscreds"
	"github.com/aws/aws-sdk-go-v2/service/dynamodb"
)

func newSafeDynamoClient() (*dynamodb.Client, error) {
	cfg, err := config.LoadDefaultConfig(/* context */)
	if err != nil {
		return nil, err
	}
	// Assume a role with scoped-down permissions for DynamoDB
	cfg.Credentials = stscreds.NewAssumeRoleProvider(
		stscreds.NewAssumeRoleProviderOptions{
			RoleARN: "arn:aws:iam::123456789012:role/DynamoDBReadOnlyRole",
			RoleSessionName: "middlebrick_scan_session",
		},
	)
	// Optionally disable SDK features that could reach metadata service
	cfg.HTTPClient = customHTTPClient()
	return dynamodb.NewFromConfig(cfg), nil
}

func customHTTPClient() *http.Client {
	// Example: disable IMDSv1 to reduce metadata exposure
	tr := &http.Transport{}
	return &http.Client{
		Transport: tr,
	}
}

3. Enforce encryption and disable endpoint discovery if not needed

Force HTTPS and avoid automatic endpoint resolution to reduce SSRF surface. Use AWS SDK options to enforce secure defaults.

import (
	"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"
)

func newSecureClient() (*dynamodb.Client, error) {
	cfg, err := config.LoadDefaultConfig(/* context */,
		config.WithEndpointResolverWithOptions(aws.EndpointResolverWithOptionsFunc(
			func(service, region string, options ...interface{}) (aws.Endpoint, error) {
				return aws.Endpoint{URL: "https://dynamodb.us-east-1.amazonaws.com"}, nil
			}),
		),
		config.WithCredentialsProvider(/* your provider */),
	)
	// Ensure all requests use HTTPS
	cfg.EndpointOptions.UseHTTPS = true
	return dynamodb.NewFromConfig(cfg), nil
}

These fixes reduce the attack surface that could enable container escape via DynamoDB. Combine them with network policies that block outbound access to 169.254.169.254 in production environments to further harden the container runtime.