Brute Force Attack in Rocket with Mutual Tls

A brute force attack against a Rocket service using mutual TLS (mTLS) focuses on exhausting authentication or rate-limiting controls rather than breaking the TLS handshake itself. In mTLS, the server validates a client certificate before application logic runs, but if the endpoint that performs certificate validation and session establishment does not enforce strict rate limits or account for authentication bypass risks, an attacker can probe that endpoint aggressively.

Consider a Rocket route that accepts mTLS and then performs additional application-level authentication (e.g., token or session checks). If the route does not apply per-client or per-certificate rate limiting before processing business logic, an attacker can open many concurrent TLS connections with different client certificates and hammer the endpoint. This shifts the attack surface from password guessing to certificate-based identity guessing, especially when client certificates are issued per user or per device without tight issuance policies.

Another scenario involves unauthenticated mTLS endpoints. If an endpoint accepts mTLS but does not require a client certificate for access, or if the server misconfigures verification to be optional, an attacker can bypass client certificate requirements and perform brute force attempts against identifiers handled by the route. Even when certificates are required, if the server does not tie certificate identity to a strong rate-limiting policy, an attacker with a valid certificate can iterate over user IDs or API keys rapidly.

OpenAPI/Swagger analysis becomes important here: if your spec describes securitySchemes of type openIdConnect or x-mtls without tying them explicitly to operation-level rate-limiting requirements, runtime findings may highlight missing throttling on mTLS-authenticated paths. Since middleBrick scans the unauthenticated attack surface and cross-references spec definitions with runtime behavior, it can flag endpoints where mTLS is accepted but rate limiting or per-identity throttling is absent.

During a scan, middleBrick’s 12 security checks run in parallel. The Rate Limiting check will test whether mTLS-authenticated paths enforce request caps per certificate or identity. The Authentication and BOLA/IDOR checks will examine whether certificate-based identities are subject to enumeration or privilege escalation. The Data Exposure and Encryption checks verify whether responses leak information that could aid brute force efforts. If the scan detects inconsistent enforcement—mTLS accepted but limits missing—it will surface a finding with severity and remediation guidance, helping you harden the service before attackers exploit the gap.

To secure Rocket with mTLS against brute force techniques, enforce strict rate limiting tied to the client certificate identity and ensure mTLS is mandatory for sensitive routes. Below are concrete, working examples using the Rocket and tls-auth crates.

1. Enforce mTLS on a route and tie rate limits to the certificate subject

// Cargo.toml dependencies:
// rocket = "0.5.0-rc.3"
// tls-auth = "0.6"
// ratelimit_meter = { version = "2", features = ["nightly"] }

use rocket::State;
use tls_auth::{TlsConnector, ServerConfig};
use std::sync::Arc;
use ratelimit_meter::LeakyBucket;
use std::collections::HashMap;
use std::time::Duration;

// A simple in-memory rate limiter keyed by certificate subject (e.g., CN)
struct RateLimitState {
    limits: tokio::sync::Mutex>,
}

#[rocket::main]
async fn main() {
    let server_config = ServerConfig::builder()
        .with_client_authentication()
        .with_single_cert(vec![], vec![]) // load your CA certs appropriately
        .expect("valid mTLS config");

    let rate_state = Arc::new(RateLimitState {
        limits: tokio::sync::Mutex::new(HashMap::new()),
    });

    rocket::build()
        .manage(server_config)
        .manage(rate_state)
        .mount("/", routes![secure_route])
        .launch()
        .await
        .unwrap();
}

#[rocket::get("/api/resource")]
async fn secure_route(
    tls_info: tls_auth::tls::TlsConnectInfo,
    rate_state: &State>,
) -> String {
    // Extract certificate subject; in real code handle missing subject gracefully
    let subject = tls_info
        .peer_certificate_subject()
        .unwrap_or("unknown")
        .to_string();

    let mut limits = rate_state.limits.lock().await;
    let bucket = limits.entry(subject.clone()).or_insert_with(|| {
        // 5 requests per minute per certificate as an example policy
        LeakyBucket::new(5, Duration::from_secs(60))
    });

    if bucket.try_consume(1).is_err() {
        return "Rate limit exceeded".to_string();
    }

    format("Hello, {}", subject)
}

use rocket::request::{self, FromRequest, Request};
use rocket::Outcome;
use tls_auth::tls::TlsConnectInfo;
use std::time::Duration;
use ratelimit_meter::LeakyBucket;
use tokio::sync::Mutex;
use std::collections::HashMap;
use std::sync::Arc;

struct OptionalTlsInfo(TlsConnectInfo);

#[rocket::async_trait]
impl<'r> FromRequest<'r> for OptionalTlsInfo {
    type Error = ();

    async fn from_request(request: &'r Request<'_>) -> request::Outcome {
        // Accept requests with or without client certs at this layer;
        // stricter enforcement happens in specific routes.
        request.guard::<&'r tls_auth::tls::TlsConnectInfo>().await
            .map(OptionalTlsInfo)
            .unwrap_or_else(|_| Outcome::Success(OptionalTlsInfo(TlsConnectInfo::default())))
    }
}

struct RateLimiter {
    limits: Mutex>,
    max_requests: u32,
    period: Duration,
}

impl RateLimiter {
    fn new(max_requests: u32, period: Duration) -> Self {
        Self {
            limits: Mutex::new(HashMap::new()),
            max_requests,
            period,
        }
    }

    async fn allow(&self, key: String) -> bool {
        let mut limits = self.limits.lock().await;
        let bucket = limits.entry(key).or_insert_with(|| LeakyBucket::new(self.max_requests, self.period));
        bucket.try_consume(1).is_ok()
    }
}

#[rocket::get("/api/data")]
async fn data_endpoint(
    tls: OptionalTlsInfo,
    limiter: &State>,
) -> String {
    let subject = if let OptionalTlsInfo(TlsConnectInfo { peer_certificates, .. }) = tls {
        peer_certificates.first()
            .map(|cert| format!("{:?}", cert.subject()))
            .unwrap_or_else(|| "no_cert".to_string())
    } else {
        "no_cert".to_string()
    };

    if limiter.allow(subject).await {
        "success".to_string()
    } else {
        "rate limit exceeded".to_string()
    }
}