Privilege Escalation in Axum (Rust)

Privilege escalation in an Axum service written in Rust typically arises from authorization gaps where an attacker can manipulate identifiers to access or modify resources belonging to other users. BOLA (Broken Object Level Authorization) and IDOR issues are common when endpoints use predictable resource IDs (e.g., user IDs, record IDs) without validating that the requesting user owns or is permitted to interact with that specific object. In Rust, this can occur even when using strong typing and the borrow checker, because authorization checks are a logical concern not enforced by the type system.

Consider an Axum handler that retrieves a user profile using a path parameter user_id. If the handler only verifies that a JWT is valid and then directly uses user_id to query a database, there is no guarantee the authenticated user matches that ID. An attacker can change the ID in the request to access another user’s data, effectively performing horizontal privilege escalation. Vertical escalation can occur if role or permission claims in the JWT are not validated on each request, allowing a user to modify their own role or tamper with token contents to gain admin-like access.

When integrating middleware or guards in Axum, it’s important to ensure the authorization logic is applied consistently and close to the data access layer. For example, extracting the user identity from the request extension and using it to scope queries (e.g., filtering by user_id in SQL WHERE clauses) is essential. If the route uses shared state such as database pools or configuration, those must be handled safely across async tasks to avoid inadvertently exposing sensitive operations due to missing checks.

Axum’s extractor model can inadvertently contribute to privilege escalation if developers rely on extractors for data but forget to re-authorize for specific actions. For instance, a handler might use a Json extractor for input and assume the server has already validated the resource ownership. In Rust, this is a logic error rather than a memory safety issue, so the compiler will not prevent it. Using path parameters, query strings, or request bodies without tying them to the authenticated subject’s permissions creates an opening for attackers to traverse relationships or escalate permissions.

Real-world patterns seen in the wild include endpoints like DELETE /users/{user_id} where an attacker changes user_id to target administrative accounts, or PATCH endpoints that modify role fields if the server does not explicitly reject modifications to sensitive attributes. Even with Rust’s safety guarantees, missing or inconsistent authorization checks in Axum handlers enable attackers to exploit IDOR/BOLA flaws to escalate privileges across horizontal (same-level) and vertical (different privilege levels) dimensions.

Remediation focuses on ensuring every data access is scoped to the authenticated subject and that authorization is re-evaluated for each operation. In Rust with Axum, this means explicitly binding the authenticated user’s ID from the request extension or JWT claims and using it to filter database queries. Never trust path parameters alone; always verify that the requesting user matches the resource owner or that the user’s role permits the action.

For example, define a UserId newtype to avoid mixing up IDs, and extract the authenticated subject in a guard or middleware so it’s available in request extensions. Then, in handlers, use that subject to construct safe queries. Below is a Rust code example using SQLx with PostgreSQL, demonstrating how to scope a user lookup by authenticated subject:

use axum::extract::Extension;
use serde::{Deserialize, Serialize};
use sqlx::PgPool;
use std::sync::Arc;

#[derive(Debug, Serialize, Deserialize)]
struct User {
    id: i64,
    username: String,
    role: String,
}

async fn get_profile_handler(
    Extension(pool): Extension>,
    axum::extract::Path(user_id): axum::extract::Path,
    current_user_id: i64, // injected by middleware/guard from JWT
) -> Result<impl axum::response::IntoResponse, (axum::http::StatusCode, String)> {
    if user_id != current_user_id {
        return Err((axum::http::StatusCode::FORBIDDEN, "Unauthorized".to_string()));
    }
    let user = sqlx::query_as!(User, "SELECT id, username, role FROM users WHERE id = $1", user_id)
        .fetch_one(pool.as_ref())
        .await
        .map_err(|e| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;
    Ok(axum::Json(user))
}

In this example, the handler compares the path user_id with the authenticated subject’s ID passed via request extension, ensuring users cannot read or modify other users’ profiles. For operations that modify sensitive fields like role, explicitly check the current user’s role and reject modifications to privileged attributes:

async fn update_role_handler(
    Extension(pool): Extension>,
    axum::extract::Path(user_id): axum::extract::Path,
    current_user_id: i64,
    current_user_role: String,
    axum::Json(payload): axum::Json<UpdateRolePayload>,
) -> Result<impl axum::response::IntoResponse, (axum::http::StatusCode, String)> {
    if current_user_role != "admin" {
        return Err((axum::http::StatusCode::FORBIDDEN, "Admins only".into()));
    }
    if user_id == current_user_id {
        return Err((axum::http::StatusCode::BAD_REQUEST, "Cannot modify self".into()));
    }
    sqlx::query!("UPDATE users SET role = $1 WHERE id = $2", payload.role, user_id)
        .execute(pool.as_ref())
        .await
        .map_err(|e| (axum::http::StatusCode::INTERNAL_SERVER_ERROR, e.to_string()))?;
    Ok(axum::StatusCode::NO_CONTENT)
}