Broken Access Control in Rocket with Mutual Tls

Broken Access Control occurs when authorization checks are missing, incomplete, or bypassed, allowing a user to access resources or perform actions they should not be able to. In Rocket, enabling Mutual TLS (mTLS) adds a layer of identity verification at the transport layer by requiring clients to present a valid certificate. However, mTLS alone does not enforce application-level authorization; it only authenticates identities. If route handlers in Rocket do not validate permissions or roles after the TLS handshake, the API can exhibit Broken Access Control.

With mTLS, the client certificate is typically mapped to a user or service identity in Rocket request guards (e.g., via tls::FromRequest). If these guards extract identity but subsequent authorization checks are omitted or incorrectly scoped (e.g., missing role checks or insufficient parameter validation), an authenticated client can access other users’ resources through IDOR-like paths or elevated privilege endpoints. This is a BOLA/IDOR scenario within the context of mTLS-protected services.

Consider a Rocket endpoint that retrieves user profile data. With mTLS enabled, any client possessing a trusted certificate can authenticate, but if the handler trusts the certificate’s subject common name to build a user identifier and does not verify that the requested profile ID matches the authenticated subject, the endpoint becomes vulnerable. An attacker who possesses a valid certificate for one account can iterate through numeric IDs or manipulate path parameters to access other profiles, demonstrating Broken Access Control despite the presence of mTLS.

Another risk arises when mTLS is used to guard administrative routes without enforcing role-based access. A certificate may be issued broadly across a service mesh, but if the handler does not check for an admin role encoded in the certificate’s extended key usage or custom fields, any mTLS-authenticated client can invoke privileged operations. This is a BFLA/Privilege Escalation vector specific to mTLS deployments where authorization is assumed from authentication alone.

Additionally, if the server does not validate certificate revocation (e.g., CRL or OCSP) and relies solely on the TLS layer to present valid certs, compromised or stale credentials can remain accepted at the application layer, further enabling unauthorized access. Proper authorization must therefore be implemented at the handler level, independent of the TLS layer, with checks aligned to the API’s access control model and compliance mappings such as OWASP API Top 10 A01:2023 and SOC2 controls.

To fix Broken Access Control in Rocket with mTLS, combine reliable identity extraction from client certificates with explicit authorization checks in each handler. Use Rocket’s TLS support to obtain the peer certificate, map it to an identity, and enforce permissions before processing requests.

First, configure Rocket to request and verify client certificates. In Rocket.toml or via programmatic configuration, ensure TLS settings require client auth:

[tls]
certificates = ["/path/server.crt"]
private_key = "/path/server.key"
client_ca = "/path/ca.crt"
require_client_auth = true

In your Rocket code, extract certificate fields via a request guard and implement authorization. For example, define a guard that extracts the subject common name and roles from certificate extensions:

use rocket::request::{self, FromRequest, Request};
use rocket::http::Status;
use openssl::x509::X509;

struct AuthUser {
    subject: String,
    roles: Vec<String>,
}

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

    async fn from_request(req: &'r Request<'>) -> request::Outcome<Self, Self::Error> {
        // Extract client certificate from TLS connection
        match req.tls_client_cert() {
            Some(cert) => {
                let subject = extract_subject(&cert);
                let roles = extract_roles(&cert);
                Outcome::Success(AuthUser { subject, roles })
            }
            None => Outcome::Failure((Status::Unauthorized, ())),
        }
    }
}

fn extract_subject(cert: &X509) -> String {
    cert.subject_name()
        .entries()
        .find(|e| e.object().to_string() == "2.5.4.3") // OID for CN
        .and_then(|e| e.data().as_utf8_str().ok())
        .map(|s| s.to_string())
        .unwrap_or_default()
}

fn extract_roles(cert: &X509) -> Vec<String> {
    // Example: read roles from a custom OID extension
    cert.extensions()
        .iter()
        .filter_map(|ext| {
            if ext.object().to_string() == "1.3.6.1.4.1.54372.1" { // custom OID
                ext.subject_key_identifier().ok().map(|skid| vec![skid.to_string()])
            } else {
                None
            }
        })
        .flatten()
        .collect()
}

With AuthUser available as a guard, enforce authorization in handlers by comparing the authenticated subject with the requested resource and checking roles:

use rocket::{get, routes};

#[get("/users/")]
fn get_user(auth: AuthUser, user_id: i32) -> String {
    // Authorization check: ensure the authenticated subject matches the requested user_id
    // Here, assume subject maps to user identifier; in practice, map via a directory service
    if auth.subject != format!("user-{user_id}") {
        return "Forbidden".to_string();
    }
    format!("Profile for {}", user_id)
}

#[get("/admin/settings")]
fn admin_settings(auth: AuthUser) -> String {
    // Role-based access control
    if !auth.roles.contains(&"admin".to_string()) {
        return "Forbidden".to_string();
    }
    "Admin settings".to_string()
}

#[rocket::main]
async fn main() -> rocket::Result<()> {
    rocket::build()
        .mount("/", routes![get_user, admin_settings])
        .launch()
        .await
}

These examples ensure that after mTLS authentication, each handler explicitly verifies permissions, preventing Broken Access Control. Combine this with centralized policy checks and regular certificate lifecycle management to maintain robust authorization in mTLS-enabled Rocket services.