Dangling Dns in Chi (Go)

When an API server in Chi uses DNS names to discover internal services (e.g., database endpoints, metadata services, or dependency backends), those DNS records become a security surface if they are not managed with strict lifecycle controls. In Go-based Chi services, this often manifests when applications rely on DNS resolution to reach backend services without validating the origin or authenticity of the resolved name. If DNS entries are left unresolved after decommissioning or if they point to unintended services via misconfigured service discovery, attackers can poison or hijack those records to redirect traffic to malicious endpoints.

In Go, DNS resolution is typically performed using net.LookupHost or the higher-level net.Dial utilities. If the resolved address is used directly to construct request URLs or TLS configurations, the application may inadvertently trust a hostname that an attacker has injected via environment variables, configuration files, or compromised service registries. This creates a dangling DNS condition where the DNS name still resolves to an IP address that the attacker controls, even though the original service has been removed or replaced.

Because Chi services often run in ephemeral environments (e.g., Kubernetes pods), the DNS cache may be reset frequently, but the application logic may still cache or reuse stale DNS entries. An attacker who can influence the DNS response—through a compromised DNS server, a malicious container image, or a compromised CI/CD pipeline—can introduce a dangling DNS record that persists across restarts. When the Chi application attempts to connect to the now-unintended service, it may expose internal endpoints, leak sensitive data, or allow privilege escalation through trusted internal communication channels.

For example, consider a Chi router that proxies requests to a backend database service named db.internal.svc.cluster.local. If this service is deleted but the DNS record is not cleaned up, a new service with the same name could be created in a different namespace or by an adversary. The Chi application continues to resolve and use the IP address, potentially connecting to an attacker-controlled database. This scenario is a textbook case of dangling DNS in a Go-powered Chi deployment.

To mitigate dangling DNS risks in Chi applications written in Go, developers must enforce strict validation of resolved hostnames and avoid relying on untrusted DNS lookups for critical internal communications. One effective pattern is to use a whitelist of known service names and verify that each resolved address matches an expected IP range or belongs to a controlled namespace. Additionally, Go applications should avoid caching DNS results across restarts and should implement short TTLs for internal service discovery.

// Example: Safe DNS resolution in Go for Chi services
func resolveService(name string) (string, error) {
    // Enforce a strict whitelist of allowed service names
    allowedServices := map[string]bool{
        "auth.internal": true,
        "cache.internal": true,
        "metrics.internal": true,
    }
    if !allowedServices[name] {
        return "", fmt.Errorf("unauthorized service name: %s", name)
    }

    // Perform DNS lookup with a short timeout
    ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
    defer cancel()

    addrs, err := net.LookupHostContext(ctx, name)
    if err != nil {
        return "", fmt.Errorf("DNS lookup failed for %s: %w", name, err)
    }

    // Validate that the resolved IP is within a trusted range
    trustedIPs := []string{"10.0.0.0/8", "192.168.0.0/16"}
    for _, addr := range addrs {
        if isIPInTrustedRange(addr, trustedIPs) {
            return addr, nil
        }
    }
    return "", fmt.Errorf("resolved IP for %s is not in a trusted range", name)
}

// Helper to check if IP is in a CIDR range
func isIPInTrustedRange(ip string, ranges []string) bool {
    parsedIP := net.ParseIP(ip)
    if parsedIP == nil {
        return false
    }
    for _, r := range ranges {
        ip, cidr, err := net.ParseCIDR(r)
        if err != nil {
            continue
        }
        if ip != nil && ip.Equal(parsedIP) && ip.Mask(cidr.Mask()) == ip {
            return true
        }
    }
    return false
}

Another remediation strategy is to replace DNS-based discovery with service mesh or gRPC health checking mechanisms that validate service identity cryptographically. In Chi, this can be achieved by integrating with Istio or Linkerd to route traffic based on mutual TLS and service intents, eliminating the need for applications to perform raw DNS lookups. By shifting trust from DNS names to the service mesh control plane, dangling DNS risks are neutralized, and the application only communicates with verified, actively running services.