Dangling Dns in Chi

Dangling DNS records in Chi applications create a critical attack vector where attackers can hijack subdomains that point to decommissioned infrastructure. In Chi's microservice architecture, this commonly occurs when services are migrated to new endpoints without properly cleaning up old DNS entries. A typical scenario involves a Chi-based API endpoint that was previously hosted at api.example.com but has since been moved to a new infrastructure. The old DNS record remains active, pointing to an IP address that's no longer under your control.

The risk escalates when Chi applications use dynamic service discovery or when containerized services rely on DNS resolution for inter-service communication. An attacker can register the IP address that your dangling DNS record points to and intercept traffic intended for your legitimate Chi service. This is particularly dangerous for Chi applications that handle authentication tokens or sensitive data, as the attacker can capture these credentials and potentially escalate privileges within your system.

Another manifestation occurs with Chi's middleware chain. If your middleware is configured to trust certain hostnames based on DNS records, a dangling record could allow an attacker to bypass authentication checks by presenting requests from a trusted but compromised subdomain. This is especially problematic when Chi applications implement CORS policies or when services use host-based routing for API versioning.

Detecting dangling DNS in Chi applications requires both network-level and application-level analysis. Start by examining your Chi application's DNS resolution patterns. Chi's http.Request object provides access to the Host header, which you should validate against your expected domain list. Here's a Chi-specific detection snippet:

package main

import (
	"github.com/go-chi/chi/v5"
	"net/http"
	"regexp"
)

var allowedDomains = regexp.MustCompile(`^([a-zA-Z0-9-]+\.)?example\.com$`)

func validateHost(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if !allowedDomains.MatchString(r.Host) {
			http.Error(w, "Invalid host", http.StatusBadRequest)
			return
		}
		next.ServeHTTP(w, r)
	})
}

func main() {
	r := chi.NewRouter()
	r.Use(validateHost)
	r.Get("/", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("Valid request"))
	})
	http.ListenAndServe(":3000", r)
}

For automated scanning, middleBrick's black-box approach is particularly effective for Chi applications. The scanner tests unauthenticated endpoints by submitting requests to your Chi API and analyzing responses for indicators of misconfiguration. It checks for inconsistent CORS policies, unexpected redirects, and services that respond to requests intended for decommissioned endpoints. middleBrick's 12 parallel security checks include specific tests for authentication bypass scenarios that could be exploited through dangling DNS records.

middleBrick also analyzes your OpenAPI/Swagger specifications if provided, cross-referencing defined endpoints with actual runtime behavior. This is crucial for Chi applications where the API contract might specify certain hostnames or base paths that no longer align with your current infrastructure.

Remediating dangling DNS in Chi applications requires a multi-layered approach. First, implement strict host validation middleware in your Chi application. Here's an enhanced version that provides more robust protection:

package main

import (
	"github.com/go-chi/chi/v5"
	"net/http"
	"strings"
)

type hostValidator struct {
	allowedHosts map[string]struct{}
}

func newHostValidator(domains ...string) *hostValidator {
	validator := &hostValidator{
		allowedHosts: make(map[string]struct{}),
	}
	for _, domain := range domains {
		validator.allowedHosts[domain] = struct{}{}
		validator.allowedHosts["www."+domain] = struct{}{}
	}
	return validator
}

func (v *hostValidator) isValidHost(host string) bool {
	if strings.HasPrefix(host, ":") {
		return true
	}
	if _, exists := v.allowedHosts[host]; exists {
		return true
	}
	return false
}

func (v *hostValidator) middleware(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if !v.isValidHost(r.Host) {
			http.Error(w, "Invalid host header", http.StatusForbidden)
			return
		}
		next.ServeHTTP(w, r)
	})
}

func main() {
	validator := newHostValidator("example.com", "api.example.com")
	r := chi.NewRouter()
	r.Use(validator.middleware)
	r.Get("/secure", func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("Secure endpoint accessed"))
	})
	http.ListenAndServe(":3000", r)
}

For DNS management, implement automated monitoring of your DNS records. Use services that alert you when records point to unexpected IP addresses or when TTL values change unexpectedly. In your CI/CD pipeline, add a step that verifies DNS records before deployment. This is where middleBrick's GitHub Action becomes valuable—you can configure it to scan your staging environment's API endpoints before they're promoted to production, catching any dangling DNS issues that might have been introduced during migration.

Additionally, implement certificate transparency monitoring. When your Chi application uses HTTPS, mismatched or unexpected certificates can indicate that traffic is being intercepted at a dangling DNS endpoint. middleBrick's encryption checks include certificate validation as part of its comprehensive security assessment, helping you identify when your TLS configuration might be vulnerable to man-in-the-middle attacks through DNS hijacking.