Arp Spoofing in Axum with Firestore

Arp spoofing is a network-layer attack where an adversary sends falsified Address Resolution Protocol messages to associate their MAC address with the IP of a legitimate host, typically the default gateway or another service in the network path. In an Axum application that communicates with Google Cloud Firestore over a shared or untrusted network segment, this attack can redirect Firestore-bound traffic through the attacker’s host. Because Firestore clients embed project and instance identifiers in every request, intercepted traffic may expose project IDs, collection paths, and potentially authentication material if encryption is not enforced or if metadata service access is also compromised.

The risk is pronounced when Axum services run in environments where network isolation is weak (for example, shared VPCs or development clusters using bridge networking). An attacker on the same subnet can inject spoofed ARP replies so that Firestore requests from Axum are silently forwarded. Although Firestore enforces strong server-side authentication and requires valid credentials, the exposure of service account tokens or application default credentials in transit can lead to token replay or session hijacking if additional protections (such as mTLS or strict firewall egress rules) are absent. This does not imply Firestore itself is insecure; rather, the network exposure created by ARP manipulation increases the attack surface for credential interception.

Compounded risks appear when developers inadvertently permit unauthenticated metadata access or rely on implicit trust within the runtime environment. For instance, if an Axum service queries Firestore using Application Default Credentials and the runtime metadata service is reachable from the same network, ARP spoofing may be coupled with SSRF or credential harvesting techniques. middleBrick’s scans highlight such combinations by correlating unauthenticated attack surface tests with network configuration findings, emphasizing the need to restrict lateral movement and enforce strict egress controls. Even with middleware protections at the application layer, a compromised host or a malicious insider on the same broadcast domain can undermine transport integrity, making robust network segmentation and encrypted channels essential.

Defending against ARP spoofing in an Axum application that uses Firestore centers on reducing network exposure and ensuring all communications are authenticated and encrypted. Place Axum services inside a private subnet with no direct internet route and use a VPC Service Controls perimeter or firewall rules to allow egress only to Firestore IP ranges. Enforce TLS for all outbound requests and validate server certificates; avoid disabling certificate verification even in development. Limit the scope of service account credentials by granting least-privilege IAM roles and prefer short-lived credentials over long-lived keys. Implement runtime network integrity checks and avoid relying on implicit trust within the local network.

Below are Axum examples that demonstrate secure Firestore usage while emphasizing network-aware practices. These snippets assume the service is deployed in a controlled environment with restricted egress.

use axum::{routing::get, Router};
use google_cloud_rust::firestore::client::Client;
use google_cloud_rust::firestore::client::ClientConfig;
use std::net::IpAddr;
use tower_http::trace::TraceLayer;

async fn build_firestore_client() -> Client {
    // Configure client with explicit project and enforced TLS
    let config = ClientConfig::new()
        .with_project_id("my-secure-project")
        .with_endpoint("firestore.googleapis.com:443")
        .with_tls()
        .expect("valid TLS configuration");
    Client::new(config).await.expect("Firestore client creation")
}

async fn fetch_document(client: &Client, collection: &str, doc_id: &str) -> Result> {
    use google_cloud_rust::firestore::client::GetDocumentRequest;
    let request = GetDocumentRequest {
        name: format!("projects/{}/databases/(default)/documents/{}/{}", client.project_id(), collection, doc_id),
        mask: None,
        transaction: None,
        read_time: None,
    };
    let doc = client.get_document(&request).await?;
    // Extract a field safely and avoid echoing raw data to logs
    let content = doc.fields.map(|f| f.to_string()).unwrap_or_else(|| "no data".to_string());
    Ok(content)
}

#[tokio::main]
async fn main() -> Result<(), Box> {
    let firestore_client = build_firestore_client().await;
    let app = Router::new()
        .route("/read/:collection/:id", get(move |axum::extract::Path((collection, id)): axum::extract::Path<(String, String)>| async move {
            fetch_document(&firestore_client, &collection, &id).await
        }))
        .layer(TraceLayer::new_for_http());

    // Bind to a private interface only; firewall should limit egress to Firestore IPs
    let listener = tokio::net::TcpListener::bind("10.0.0.10:3000").await?;
    axum::serve(listener, app).await?;
    Ok(())
}

In this setup, the service binds to a private interface and uses explicit TLS endpoints. Network-level controls should ensure that only the defined IP ranges for Firestore are allowed as egress. Combine this with IAM conditions and, where possible, private service connect endpoints to further reduce exposure to network-layer attacks such as ARP spoofing.