Broken Access Control in Axum with Api Keys

Broken Access Control in an Axum service that uses API keys typically arises when authorization checks are missing, inconsistent, or incorrectly applied after key validation. Axum is a web framework for Rust that encourages explicit routing and handler composition; security relies on developers to enforce authorization at each relevant endpoint. If API keys are validated once (for example via middleware or a request guard) but the handler or downstream service logic does not re-check role-based or ownership constraints, an authenticated key can be leveraged to access or modify resources that should be restricted.

Consider an endpoint like /organizations/{org_id}/settings that accepts an API key in an Authorization: ApiKey <key> header. A key might be issued to an organization member, but if the handler only verifies the key and does not verify that the member has permission for the specific org_id in the request, this becomes a BOLA/IDOR pattern. Attackers can enumerate or guess IDs and call the endpoint with a valid key that lacks scope, effectively bypassing intended access boundaries. Similarly, privilege escalation can occur when an API key with read-only scopes is accepted by a handler that performs write actions because the developer assumed the middleware’s key scope would block misuse; without explicit checks in the handler, such misalignment enables unauthorized operations.

Another common pattern is key-to-role mapping stored in a database or configuration. If this mapping is loaded once at startup and cached, but role changes are not reflected promptly, stale data can allow elevated permissions to persist. In Axum, if a guard extracts claims from a key and inserts them into request extensions, handlers must still validate that those claims permit the requested action on the target resource. Missing or incomplete checks in handlers, especially for sensitive operations like deleting resources or changing billing, constitute Broken Access Control under the OWASP API Top 10 and can map to violations of least privilege and insufficient authorization checks.

Runtime findings from middleBrick scans often reveal such issues when endpoints accept authenticated requests but lack per-resource authorization, exhibit missing role checks, or allow key reuse across tenants without isolation. Because Axum does not enforce authorization implicitly, developers must design each route to validate scope, tenant membership, and object ownership explicitly. middleBrick’s checks for BOLA/IDOR, BFLA/Privilege Escalation, and Property Authorization highlight these gaps by correlating spec definitions with runtime behavior, ensuring that even authenticated calls are verified for proper authorization context.

Remediation centers on ensuring that after an API key is validated, each handler enforces fine-grained authorization. Below is a concise, realistic Axum example showing key validation, role extraction, and per-request ownership checks for an endpoint that manages organization settings.

use axum::{routing::get, Router, extract::Extension, http::Request, async_trait};
use std::net::SocketAddr;
use serde::{Deserialize, Serialize};

// Domain models
#[derive(Debug, Clone, Serialize, Deserialize)]
struct ApiKey { key: String, org_id: String, scopes: Vec }

#[derive(Debug, Clone, Serialize, Deserialize)]
struct OrgSettings { org_id: String, billing_email: String }

// Simulated key lookup (replace with DB/cache lookup)
async fn resolve_key(key: &str) -> Option<ApiKey> {
    match key {
        "valid-org-123-read" => Some(ApiKey { key: key.to_string(), org_id: "org-123".to_string(), scopes: vec!["read".to_string()] }),
        "valid-org-123-write" => Some(ApiKey { key: key.to_string(), org_id: "org-123".to_string(), scopes: vec!["write".to_string()] }),
        _ => None,
    }
}

// Authorization guard: ensures key is valid and has required scope
async fn require_scope(
    required_scope: &'static str,
) -> axum::impl_tower::Layer<axum::routing::BoxRoute<(), (), <Router<(), <() as axum::routing::routing::MakeRouter<()>>::RouterBody>>>
where
    (): axum::extract::FromRequest<State = <Router<(), <() as axum::routing::routing::MakeRouter<()>>::RouterBody>>,
{
    // Implementation omitted for brevity; in practice this would validate key and attach ApiKey to request extensions
    unimplemented!()
}

// Handler with explicit authorization
async fn get_settings(
    Extension(key): Extension<ApiKey>,
    org_id: String,
) -> Result<axum::Json<OrgSettings>, (axum::http::StatusCode, String)> {
    // Explicit resource-level authorization: key must own or have permission for this org_id
    if key.org_id != org_id {
        return Err((axum::http::StatusCode::FORBIDDEN, "Access denied".to_string()));
    }
    if !key.scopes.contains(&"read".to_string()) {
        return Err((axum::http::StatusCode::FORBIDDEN, "Insufficient scope".to_string()));
    }
    // Fetch settings for the validated org_id
    let settings = OrgSettings { org_id, billing_email: "[email protected]".to_string() };
    Ok(axum::Json(settings))
}

#[tokio::main]
async fn main() {
    let app = Router::new()
        .route("/organizations/:org_id/settings", get(get_settings));
    // In production, integrate key resolution into a proper request guard or middleware
    let listener = tokio::net::TcpListener::bind("127.0.0.1:3000").unwrap();
    axum::serve(listener, app).await.unwrap();
}

This example demonstrates the critical pattern: after resolving the key (here simplified), the handler compares the key’s org_id with the requested path parameter and verifies required scopes before proceeding. For write operations, require a write scope and consider additional checks such as idempotency keys or rate limiting to reduce abuse impact.

When using a shared configuration or caching layer for key metadata, ensure that updates propagate without long-lived stale caches; otherwise, permission changes may not take effect immediately. middleBrick’s Pro plan supports continuous monitoring and can alert you when risk patterns related to authorization drift are detected across your API surface, helping you maintain consistent enforcement as configurations evolve.

Finally, validate inputs rigorously (e.g., ensure org_id is a valid UUID or integer) and avoid relying solely on key-based routing to enforce tenant boundaries. Combine explicit handler checks with robust key lifecycle management to reduce the likelihood of Broken Access Control in Axum services.