Api Abuse in Axum (Rust)

Axum is a popular Rust web framework that emphasizes type safety and ergonomic routing. When building APIs in Axum, developers often focus on correctness and performance, sometimes overlooking authorization and input validation patterns that enable Api Abuse. Api Abuse covers scenarios such as BOLA/IDOR, BFLA/Privilege Escalation, and Property Authorization issues, where attackers manipulate parameters to access or modify resources they should not.

In Axum, routes are composed using extractors like Path, Query, and Json. If numeric IDs or identifiers are extracted without verifying ownership or scope, an attacker can change the ID in the request and access another user’s data. For example, an endpoint like /users/{user_id}/profile that only validates authentication but not whether the authenticated subject owns the provided user_id is vulnerable to BOLA. Similarly, operations that perform state changes (e.g., updating or deleting a resource) without confirming that the requesting actor has permission for that specific resource can lead to privilege escalation or unauthorized modifications.

Rust’s type system and ownership model reduce many classes of memory-safety bugs but do not prevent logical flaws in authorization. An Axum handler written in Rust might deserialize a request into a strongly-typed struct and assume the developer has already enforced constraints. If authorization checks are scattered or omitted, the API surface remains exposed. For instance, using a shared database connection and constructing queries directly from path or query parameters without scoping to the requester can lead to unauthorized data access. Rate limiting and input validation are also critical; without them, attackers can probe endpoints for IDs, trigger excessive operations, or abuse expensive endpoints to cause denial-of-service or financial impact.

middleBrick detects these patterns by analyzing the OpenAPI spec and runtime behavior. For Axum services, it checks whether route parameters are properly scoped to the authenticated subject, whether queries enforce tenant or user boundaries, and whether operations that mutate state include appropriate authorization. It also validates input constraints and inspects rate-limiting configurations to ensure that abuse vectors such as credential stuffing or resource enumeration are mitigated. The scanner highlights findings such as missing ownership checks on Path parameters and missing role-based constraints on mutating routes.

Securing Axum endpoints in Rust requires explicit authorization checks, careful scoping of queries, and robust input validation. Below are concrete patterns and code examples to address common Api Abuse risks.

1. Preventing BOLA/IDOR with ownership checks

Always scope data access to the authenticated subject. If you store a user ID in the session or JWT claims, use it to filter database queries rather than relying solely on the path parameter.

// Good: scope profile lookup to the authenticated user
async fn get_user_profile(
    Extension(state): Extension<AppState>,
    Path(user_id): Path<Uuid>,
    Claims(claims): Option<Claims>,
) -> Result<Json<UserProfile>, (StatusCode, String)> {
    let claims = claims.ok_or((StatusCode::UNAUTHORIZED, "missing claims"))?;
    if claims.user_id != user_id {
        return Err((StatusCode::FORBIDDEN, "access denied".to_string()));
    }
    let profile = state
        .db
        .fetch_user_profile(user_id)
        .await
        .map_err(|_| (StatusCode::INTERNAL_SERVER_ERROR, "db error"))?;
    Ok(Json(profile))
}

2. Enforce tenant or organization boundaries

For multi-tenant APIs, include tenant identifiers in queries and verify that the resource belongs to the tenant making the request.

// Good: enforce tenant scope on organization resource
async fn update_settings(
    Extension(state): Extension<AppState>,
    Path(org_id): Path<Uuid>,
    Json(payload): Json<SettingsUpdate>,
    Claims(claims): Claims<OrgClaims>,
) -> Result<StatusCode, (StatusCode, String)> {
    if claims.organization_id != org_id {
        return Err((StatusCode::FORBIDDEN, "tenant mismatch".into()));
    }
    state
        .db
        .update_settings_for_org(org_id, &payload)
        .await
        .map_err(|_| (StatusCode::INTERNAL_SERVER_ERROR, "update failed".into()))?;
    Ok(StatusCode::NO_CONTENT)
}

3. Validate and constrain inputs

Use strong types and validation libraries (e.g., validator) to reject malformed or suspicious inputs before they reach business logic.

// Good: validate input length and format
use validator::Validate;

#[derive(Validate)]
struct CreateItem {
    #[validate(length(min = 1, max = 100))]
    name: String,
    #[validate(range(min = 1))]
    quantity: i32,
}

async fn create_item(Json(payload): Json<CreateItem>) -> Result<StatusCode, (StatusCode, String)> {
    payload.validate().map_err(|e| (StatusCode::BAD_REQUEST, e.to_string()))?;
    // proceed with creation
    Ok(StatusCode::CREATED)
}

4. Apply rate limiting at the route or service level

Use Axum middleware to limit repeated requests from a single source, reducing enumeration and brute-force risks.

// Example: simple rate limit with tower-limit
use tower_limit::RateLimitLayer;
use std::time::Duration;

let app = Router::new()
    .route("/api/data", get(fetch_data))
    .layer(RateLimitLayer::new(100, Duration::from_secs(60)));

5. Use method-based authorization for mutating operations

Ensure that POST, PUT, DELETE, and PATCH endpoints verify permissions specific to the action and resource.

// Good: action-specific authorization
async fn delete_item(
    Extension(state): Extension<AppState>,
    Path(id): Path<Uuid>,
    Claims(claims): Claims<UserClaims>,
) -> Result<StatusCode, (StatusCode, String)> {
    let item = state.db.fetch_item(*id).await.map_err(...)?;
    if !state.authz.can_delete(&claims, &item) {
        return Err((StatusCode::FORBIDDEN, "cannot delete".into()));
    }
    state.db.delete_item(*id).await.map_err(...)?;
    Ok(StatusCode::NO_CONTENT)
}

By combining these patterns, Rust developers using Axum can mitigate common Api Abuse vectors. Remember that middleBrick can scan your OpenAPI specification and runtime behavior to highlight missing ownership checks, weak tenant scoping, and insufficient input validation, helping you focus remediation efforts where they are most needed.