Idor Enumeration in Axum (Rust)

In Axum, an HTTP framework for Rust, developers typically define routes with path parameters such as /users/{user_id} and then extract those parameters into typed values. When authorization checks are missing or incomplete, attackers can perform Idor Enumeration by iterating over sequential or predictable identifiers and observing differences in HTTP responses. For example, a handler that retrieves a user profile without verifying that the requesting user owns the requested user_id may leak information through timing differences, verbose error messages, or the presence or absence of data.

Rust’s type system and Axum’s extractor model encourage explicit handling of path parameters, but they do not enforce authorization. If a developer writes an extractor like user_id: u64 and uses it directly in a database query without scoping to the authenticated subject, the endpoint becomes an enumeration surface. An attacker can send requests for IDs 1, 2, 3, and so on, and infer valid records from subtle differences in response content or timing. This is especially risky when responses include stack traces or detailed validation messages that reveal internal structures or existence of resources.

Common patterns that lead to Idor Enumeration include using database offsets for pagination without ownership checks, embedding record IDs in URLs without tenant or user scoping, and failing to apply consistent policy checks across related endpoints. In Rust, because the compiler ensures memory safety, the vulnerability is rarely a null or out-of-bounds access; instead it is a logic flaw where the application returns 200 with data versus 404 or 403, enabling automated enumeration scripts to map accessible resources.

Real-world attack patterns mirror those described in the OWASP API Top 10 (2023) and map to controls in frameworks such as SOC2 and GDPR. For instance, an endpoint like GET /api/v1/organizations/{org_id}/settings that only checks that the ID is a valid integer can allow an attacker to enumerate organization IDs and probe for sensitive configurations. The Axum handler may return structured JSON that differs subtly depending on whether the requester has permission, giving an attacker actionable signals without triggering rate limits or authentication requirements.

Because middleBrick scans test unauthenticated attack surfaces and include Idor checks among the 12 parallel security checks, endpoints with predictable numeric identifiers and missing ownership validation are likely to be flagged. The scanner does not rely on internal architecture, but on runtime responses, so it can detect enumeration behavior by observing status codes, response sizes, and timing consistency across sequential IDs.

Remediation in Axum with Rust centers on ensuring that every data retrieval is scoped to the authenticated subject and that responses are consistent for unauthorized or non-existent resources. Use extractor combinators and middleware to inject the subject identity, then enforce row-level ownership in the data access layer before returning any payload.

Below is a minimal, idiomatic Axum handler that demonstrates secure handling of a user profile endpoint. It uses a mock repository pattern to illustrate scoping; in production you would replace this with a database query that filters by both the resource ID and the authenticated user ID or tenant ID.

use axum::extract::State;
use serde::Serialize;

#[derive(Clone)]
struct AppState {
    // In practice, pass a repository or service that is scoped to a tenant or user.
    user_repo: UserRepository,
}

#[derive(Serialize)]
struct UserProfile {
    id: u64,
    username: String,
    email: String,
}

async fn get_user_profile(
    State(state): State<AppState>,
    axum::extract::Path(user_id): axum::extract::Path<u64>,
    // Assume an extractor that provides the authenticated subject.
    auth_subject: AuthenticatedSubject,
) -> Result<impl IntoResponse, (StatusCode, String)> {
    // Scope the lookup to the combination of user_id and the authenticated subject.
    let profile = state.user_repo.find_by_id_and_subject(user_id, auth_subject.user_id).await;
    match profile {
        Some(p) => Ok(axum::Json(p)),
        None => // Return a generic not-found to prevent enumeration.
            Err((StatusCode::NOT_FOUND, "Not found".to_string())),
    }
}

The key remediation steps are: (1) require an authenticated subject via an extractor such as JWT claims; (2) pass that subject into the repository or service layer; (3) construct queries that filter on both the resource identifier and the subject, ensuring that users can only access their own records; and (4) return the same HTTP status for non-owned and non-existent resources to eliminate timing and content-based leakage.

For paginated endpoints, avoid exposing total counts or offsets that hint at the existence of other records. Instead, scope the query to the authenticated user’s set and return opaque cursors if needed. MiddleBrick’s scans can detect differences in response size and status codes across IDs, so consistent error handling and uniform response shapes are important controls to reduce the scanner’s findings.

When using OpenAPI specs with Axum, ensure that path parameters are described clearly and that security schemes are referenced so that generated clients and documentation reflect the need for authentication. While middleBrick’s OpenAPI/Swagger spec analysis resolves $ref and cross-references definitions with runtime findings, developers must still enforce scoping in code; the scanner will highlight endpoints where authentication is missing or where responses suggest possible enumeration.

In the Pro plan, continuous monitoring can be configured to alert if the scanner detects status code patterns consistent with Idor Enumeration across sequential IDs. The GitHub Action can fail builds when new endpoints introduce path parameters without corresponding ownership checks, and the CLI can output JSON for integration into local development workflows.