Fix Business Logic Errors in Actix Web | GuardAPI Security Guide

Memory safety in Rust doesn't save you from logical catastrophes. In Actix Web, business logic errors—specifically IDOR (Insecure Direct Object Reference) and state corruption—are the silent killers. If you are trusting the client-provided ID without server-side ownership verification, your application is structurally compromised regardless of how fast the binary is.

The Vulnerable Pattern

#[post("/api/v1/profile/{user_id}/update")]
async fn update_profile(
    path: web::Path,
    payload: web::Json,
    db: web::Data
) -> impl Responder {
    let user_id = path.into_inner();
    // VULNERABILITY: The handler trusts user_id from the URL.
    // Any authenticated user can supply another user's ID to modify their data.
    match db.exec_update(user_id, &payload).await {
        Ok(_) => HttpResponse::Ok().json("Profile updated"),
        Err(_) => HttpResponse::InternalServerError().finish(),
    }
}

The Secure Implementation

The vulnerability is a classic IDOR. The handler blindly accepts a 'user_id' from the URI path and performs a mutation. A hacker simply iterates the integer in the URL to hijack any account. The fix implements an Authorization layer using the 'actix-identity' extractor. By comparing the 'Identity' (derived from a secure, server-side session or encrypted JWT) against the requested resource ID, we ensure that the Subject is authorized to modify the Object. Always treat client-provided parameters as untrusted triggers and use session-backed state as the source of truth for permissions.

use actix_identity::Identity;
#[post(“/api/v1/profile/{user_id}/update”)]
async fn update_profile(
path: web::Path,
payload: web::Json,
identity: Identity,
db: web::Data
) -> impl Responder {
let target_user_id = path.into_inner();
// SECURE: Extract identity from secure cookie/session
let auth_user_id = match identity.id() {
    Ok(id) => id.parse::<u32>().unwrap_or(0),
    Err(_) => return HttpResponse::Unauthorized().finish(),
};

// AUTHORIZATION CHECK: Ensure the actor owns the resource
if target_user_id != auth_user_id {
    return HttpResponse::Forbidden().json("Access Denied: Ownership Mismatch");
}

match db.exec_update(target_user_id, &payload).await {
    Ok(_) => HttpResponse::Ok().json("Profile updated"),
    Err(_) => HttpResponse::InternalServerError().finish(),
}
}

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The Vulnerable Pattern

The Secure Implementation

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