Dangling Dns in Actix
How Dangling DNS Manifests in Actix
Dangling DNS records in Actix applications occur when DNS entries point to infrastructure that no longer hosts the intended Actix web service. This creates a scenario where attackers can claim the orphaned infrastructure and intercept traffic meant for your Actix application.
In Actix applications, this commonly manifests through:
- Subdomain takeover via abandoned Heroku, AWS, or GCP deployments that previously hosted Actix services
- CNAME records pointing to deleted S3 buckets or CloudFront distributions that served Actix assets
- A records pointing to decommissioned EC2 instances that ran Actix applications
- API Gateway endpoints that were removed but still referenced in DNS
The attack pattern typically follows this sequence:
- Attacker discovers a dangling DNS record (e.g., api.old-service.example.com)
- Attacker provisions infrastructure matching the original service type
- Attacker deploys a malicious Actix application to intercept requests
- Victim traffic flows to attacker-controlled infrastructure
For Actix specifically, attackers might deploy a minimal Actix application that mimics the original service's API structure to capture authentication tokens, session cookies, or sensitive data. Since Actix applications often handle JSON APIs, the attacker can create routes that mirror the legitimate service's endpoints to collect payloads.
use actix_web::{web, App, HttpServer, Responder};
async fn malicious_endpoint(data: web::Json<serde_json::Value>) -> impl Responder {
// Log or exfiltrate the received data
web::Json(data.0)
}
#[actix_web::main]
async fn main() -> std::io::Result<()> {
HttpServer::new(|| {
App::new()
.service(web::resource("/api/v1/data").route(web::post().to(malicious_endpoint)))
})
.bind("0.0.0.0:8080")?
.run()
.await
}This Actix code snippet demonstrates how an attacker could quickly deploy a service to capture JSON payloads from endpoints they've taken over through dangling DNS.
Actix-Specific Detection
Detecting dangling DNS issues in Actix deployments requires both infrastructure scanning and runtime verification. middleBrick's black-box scanning approach is particularly effective for this scenario.
When scanning Actix applications, middleBrick performs these specific checks:
- Attempts to connect to all discovered endpoints and analyzes HTTP responses
- Looks for Actix-specific headers like
X-ActixorServer: actixin responses - Tests for common Actix route patterns (/api/, /health/, /metrics/)
- Verifies TLS certificate validity and hostname matching
- Checks for default Actix error pages that might indicate a newly deployed application
For manual detection in Actix applications, examine your deployment configurations:
// Check your Actix deployment configurations
// Look for hardcoded endpoints or service references
let bind_address = "0.0.0.0:8080"; // Verify this matches your DNS records
// Check for external service integrations
let external_api = "https://api.example.com"; // Ensure this domain is still valid
// Verify TLS configurations
let cert_path = "cert.pem"; // Check certificate expiration and domain coveragemiddleBrick's scanning can identify dangling DNS issues by detecting when Actix applications respond with unexpected content or default configurations. The scanner tests multiple endpoints simultaneously and compares responses against known Actix patterns.
Key indicators that middleBrick might flag:
- Actix default error pages appearing on production endpoints
- Unexpected Actix version headers in responses
- Missing expected Actix middleware (CORS, auth)
- Default Actix port bindings (8080, 3000) responding to production DNS
Actix-Specific Remediation
Remediating dangling DNS issues in Actix deployments requires both infrastructure changes and application-level safeguards. Here are Actix-specific approaches:
First, implement proper health checks and monitoring in your Actix application:
use actix_web::{dev::ServiceRequest, dev::ServiceResponse, Error};
use actix_http::body::Body;
async fn health_check(req: ServiceRequest, srv: &mut actix_web::dev::Service<ServiceRequest>) -> Result<ServiceResponse, Error> {
let res = srv.call(req).await?;
// Check if response indicates a default/undeployed Actix app
if let Ok(body) = res.body().as_bytes() {
if body.contains(&b"Actix Web"[..]) || body.contains(&b"404 Not Found"[..]) {
// Log or alert on unexpected default responses
}
}
Ok(res)
}Second, secure your Actix application against unauthorized deployments:
use actix_web::{middleware, App, HttpServer};
use actix_cors::Cors;
#[actix_web::main]
async fn main() -> std::io::Result<()> {
HttpServer::new(|| {
App::new()
.wrap(middleware::NormalizePath::default())
.wrap(Cors::default())
.wrap(middleware::Logger::default())
.configure(secure_routes)
})
.bind("0.0.0.0:8080")?
.run()
.await
}
fn secure_routes(cfg: &mut web::ServiceConfig) {
cfg.service(
web::resource("/api/health").route(web::get().to(health_check_handler))
);
// Only register production routes after verification
if is_production_deployment() {
cfg.service(api_routes());
}
}Third, implement domain verification and certificate pinning:
use actix_tls::rustls::RustlsConfig;
use rustls_pemfile::{certs, read_one}
async fn verify_domain_identity() -> Result<(), std::io::Error> {
let config = RustlsConfig::new();
// Verify TLS certificate matches expected domains
let cert = config.get_certificate();
let cert_domains = cert.get_domains();
let expected_domains = ["api.example.com", "example.com"];
for domain in expected_domains {
if !cert_domains.contains(&domain) {
return Err(std::io::Error::new(std::io::ErrorKind::Other, "Domain mismatch"));
}
}
Ok(())
}Finally, integrate middleBrick scanning into your Actix deployment pipeline:
#!/bin/bash
# CI/CD integration for Actix deployments
set -e
# Scan before deployment
echo "Scanning Actix API endpoints..."
middlebrick scan https://api.example.com --output json > scan_results.json
# Check scan results
if grep -q "Dangling DNS" scan_results.json; then
echo "Dangling DNS detected! Aborting deployment."
exit 1
fi
echo "Deployment can proceed - no dangling DNS detected."