Insecure Design in Actix with Firestore

Insecure design in an Actix web service that uses Google Cloud Firestore as the primary data store often stems from modeling application permissions and data access patterns at the wrong layer. When authorization logic is implemented as ad-hoc checks scattered across Actix handlers, or when Firestore security rules are treated as a secondary safety net rather than the source of truth, the overall design becomes vulnerable to Insecure Direct Object References (IDOR) and broader authorization flaws (BOLA). The risk is elevated because Firestore rules are evaluated with the privileges of the service account used by the backend, which can inadvertently grant broad read or write access if rules are permissive.

For example, consider an Actix handler that retrieves a user document by ID directly from Firestore using a user-supplied identifier without validating ownership. If the handler uses a service account with broad read access, the request will succeed regardless of whether the requesting user is allowed to view that resource. This design assumes the handler enforces ownership, but if that check is missed or bypassed, Firestore returns the data, leading to unauthorized data exposure. Similarly, Firestore’s lack of native row-level permissions means that once a reference or query is constructed, the data is returned unless rules intervene. If rules are coarse-grained (e.g., allowing read on entire collections), the backend must compensate with strict checks; missing checks in Actix handlers then translate directly into insecure data exposure.

Another insecure design pattern involves how Firestore listeners and queries are set up in Actix background tasks or long-running handlers. If a query uses a non-validated path parameter to select a collection or document, and the security rules are not aligned with the principle of least privilege, the backend can expose data across tenants or users. For instance, using a path like users/{user_id}/orders/{order_id} where user_id is taken directly from a request without confirming that the authenticated subject matches that ID is a classic BOLA flaw. Firestore will return the data if rules permit it, and Actix will return it to the client, even when the user should not have access. This becomes a systemic design issue when authorization context is not consistently derived from the authenticated identity on every request.

Insecure design also appears in how Firestore data is structured and indexed. Overly broad collection group queries or deeply nested maps intended for convenience can become exposure vectors when Actix handlers iterate over results without enforcing tenant isolation or scope boundaries. If security rules allow broad queries and the handler does not explicitly filter by user ID, the combination can return data from other users. Additionally, storing sensitive fields without considering Firestore’s encryption-at-rest and in-transit protections can lead to Data Exposure findings, even if the service account is tightly scoped. Therefore, the design must treat Firestore rules and Actix handler logic as mutually reinforcing controls, where each layer explicitly validates scope, ownership, and context to avoid insecure outcomes.

Remediation centers on enforcing ownership and scope checks in Actix handlers and aligning Firestore security rules with the principle of least privilege. Always derive the user identity from the authenticated session and use it to scope every Firestore read, write, or query. Below are concrete, realistic code examples that demonstrate secure patterns for an Actix service using Firestore via the official Google Cloud client library.

Secure handler with explicit ownership check

In this example, the handler extracts the authenticated user’s ID from request extensions (set by an authentication middleware) and uses it to construct a scoped document reference. This ensures that a user can only access their own orders, regardless of what ID is provided in the request path.

use actix_web::{web, HttpResponse, Result};
use google_cloud_firestore::client::Client;
use google_cloud_firestore::document::Document;

async fn get_user_order(
    path: web::Path<(String, String)>,
    client: web::Data,
    user_identity: web::ReqData, // authenticated user ID from middleware
) -> Result {
    let (user_id_from_path, order_id) = path.into_inner();
    let user_identity = user_identity.into_inner();

    // Enforce ownership: the user can only access their own orders
    if user_id_from_path != user_identity {
        return Ok(HttpResponse::Forbidden().body("Unauthorized access to order"));
    }

    let doc_ref = client
        .document(&format!("users/{}/orders/{}", user_identity, order_id));
    let document = doc_ref.get().await.map_err(|e| {
        actix_web::error::ErrorInternalServerError(e.to_string())
    })?;

    if document.exists() {
        Ok(HttpResponse::Ok().json(document.data().unwrap_or_default()))
    } else {
        Ok(HttpResponse::NotFound().body("Order not found"))
    }
}

Scoped query using authenticated user identity

This handler demonstrates how to perform a scoped query that respects tenant boundaries. The user identity is used to constrain the query to a specific subcollection, preventing cross-user data leakage even if Firestore rules are inadvertently broad.

async fn list_user_orders(
    client: web::Data,
    user_identity: web::ReqData,
) -> Result {
    let user_identity = user_identity.into_inner();
    let col_ref = client.collection(&format!("users/{}/orders", user_identity));
    let snapshot = col_ref.list().await.map_err(|e| {
        actix_web::error::ErrorInternalServerError(e.to_string())
    })?;

    let orders: Vec = snapshot.docs.into_iter().collect();
    Ok(HttpResponse::Ok().json(orders))
}

Firestore security rules aligned with Actix checks

Security rules should mirror the ownership checks performed in Actix. Rules should scope reads and writes to documents where the user ID in the path matches the authenticated UID. This layered approach ensures that even if a handler is misconfigured, rules can prevent unauthorized access.

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /users/{user_id}/orders/{orderId} {
      allow read, write: if request.auth != null && request.auth.uid == user_id;
    }
  }
}

Avoiding collection group queries without strict scoping

If a feature requires collection group queries, always filter by user ID in both the query and the rules. Do not rely on rules alone to enforce tenant isolation when the query retrieves broader sets of data.

async fn search_user_orders(
    client: web::Data,
    user_identity: web::ReqData,
) -> Result {
    let user_identity = user_identity.into_inner();
    // Use collection group but filter by user path component explicitly
    let col_ref = client.collection_group("orders")
        .where_filter("user_id", "==", user_identity);
    let snapshot = col_ref.list().await.map_err(|e| {
        actix_web::error::ErrorInternalServerError(e.to_string())
    })?;

    let orders: Vec = snapshot.docs.into_iter().collect();
    Ok(HttpResponse::Ok().json(orders))
}

By combining strict identity checks in Actix handlers with scoped Firestore references and aligned security rules, the design avoids insecure direct object references and ensures that data exposure risks are minimized across the stack.