Insecure Design in Echo Go with Firestore

Insecure Design in an Echo Go service that uses Firestore often arises from trusting client-supplied identifiers and modeling data without considering authorization boundaries. Firestore security rules rely heavily on the structure of your data and the identifiers you embed in document paths; if those identifiers reflect user IDs or roles supplied directly by the client, an attacker can manipulate path segments to reach other users’ documents. In Go handlers built with Echo, developers may bind path parameters (e.g., :userID) and then concatenate them into Firestore document references without verifying that the authenticated actor owns that ID. This becomes an Insecure Design issue when the server assumes the client-provided ID is trustworthy, effectively exposing BOLA/IDOR-like behavior at the application layer rather than enforcing ownership checks in rules and code.

Another common pattern is modeling data per user but failing to scope queries to the requester’s tenant or identity. For example, a handler might read a list of documents from a collection group without filtering by the authenticated user’s organization or by validating that the requested resource belongs to the same tenant as the caller. Because Firestore queries return matching documents across the collection unless rules block them, an Insecure Design flaw here means the server-side logic does not enforce tenant or ownership scoping, allowing enumeration or unauthorized reads. The Echo middleware may parse tokens and set context, but if the handler does not use that context to constrain Firestore access, the design is insecure even when rules are partially restrictive.

Additionally, Firestore’s flexible schema can encourage designs where sensitive flags or administrative fields are stored alongside regular data and relied upon solely by the server for access decisions. If an Echo Go handler reads a document and checks a field like role or isAdmin without verifying that the field cannot be tampered with by the client, the design is vulnerable to privilege escalation. A client cannot directly modify Firestore server-side rules, but they can attempt to write malicious fields that the server might trust if input validation and field-level authorization are omitted. This intersects with BFLA and Property Authorization checks: the server must treat all client-supplied data as untrusted and enforce authorization on every request, not on assumed invariants modeled in the client.

These issues are detectable by middleBrick’s 12 security checks, including BOLA/IDOR, Property Authorization, and Unsafe Consumption scans, which highlight insecure patterns where Echo handlers interact with Firestore without proper scoping or validation. Because Firestore rules cannot fully compensate for missing server-side ownership checks, the combination of Echo Go routing and Firestore data access requires disciplined design: always bind authenticated identity server-side, scope queries and document paths to that identity, and validate that each field used in authorization is backed by server-enforced rules rather than client-controlled values.

To remediate Insecure Design when using Echo Go with Firestore, enforce authorization on the server by deriving document paths from authenticated identity rather than client input, and scope all reads and writes accordingly. Below is a secure pattern that retrieves a user document using the authenticated UID from the JWT, avoiding any direct use of client-supplied identifiers for document paths.

// Example: secure handler using Echo and Firestore
func GetUserProfile(c echo.Context) error {
    // Authenticated UID from middleware, not from path or query
    uid, ok := c.Get("uid").(string)
    if !ok || uid == "" {
        return c.JSON(http.StatusUnauthorized, map[string]string{"error": "unauthorized"})
    }

    ctx := c.Request().Context()
    client, err := firestore.NewClient(ctx, <your-project-id>)
    if err != nil {
        return c.JSON(http.StatusInternalServerError, map[string]string{"error": "internal error"})
    }
    defer client.Close()

    // Document path derived from server-side identity
    docRef := client.Collection("users").Doc(uid)
    docSnap, err := docRef.Get(ctx)
    if err != nil {
        return c.JSON(http.StatusInternalServerError, map[string]string{"error": "unable to load profile"})
    }
    if !docSnap.Exists() {
        return c.JSON(http.StatusNotFound, map[string]string{"error": "not found"})
    }

    var profile map[string]interface{}
    if err := docSnap.DataTo(&profile); err != nil {
        return c.JSON(http.StatusInternalServerError, map[string]string{"error": "unable to parse"})
    }
    return c.JSON(http.StatusOK, profile)
}

When querying collections that must be scoped to the authenticated user or tenant, always include the server-derived identifier in the query rather than trusting client filters. For example, if each organization has its own subcollection, use the authenticated UID or an organization ID verified server-side to limit the query scope.

// Secure collection query scoped by authenticated UID
func ListUserItems(c echo.Context) error {
    uid, ok := c.Get("uid").(string)
    if !ok || uid == "" {
        return c.JSON(http.StatusUnauthorized, map[string]string{"error": "unauthorized"})
    }

    ctx := c.Request().Context()
    client, err := firestore.NewClient(ctx, <your-project-id>)
    if err != nil {
        return c.JSON(http.StatusInternalServerError, map[string]string{"error": "internal error"})
    }
    defer client.Close()

    // Scope query to the authenticated user’s items
    iter := client.Collection("users").Doc(uid).Collection("items").Documents(ctx)
    defer iter.Stop()

    var items []map[string]interface{}
    for {
        doc, err := iter.Next()
        if err == iterator.Done {
            break
        }
        if err != nil {
            return c.JSON(http.StatusInternalServerError, map[string]string{"error": "unable to list items"})
        }
        var data map[string]interface{}
        if err := doc.DataTo(&data); err != nil {
            continue // or handle appropriately
        }
        items = append(items, data)
    }
    return c.JSON(http.StatusOK, items)
}

For Firestore security rules, complement these server-side checks with rules that enforce ownership using request.auth.uid, but remember that rules are a safety net and not a replacement for server-side scoping. Define rules that require the document or collection group path to contain the authenticated UID, and avoid rules that allow broad read access based on client-supplied path components.

// Firestore rule example (for context, not executable Go)
rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /users/{userId} {
      allow read, write: if request.auth != null && request.auth.uid == userId;
      match /items/{itemId} {
        allow read, write: if request.auth != null && request.auth.uid == userId;
      }
    }
  }
}

By combining server-side identity derivation, strict scoping in queries, and conservative rules, you remove the insecure design pattern where Echo Go routes or Firestore paths are influenced by unvalidated client input. This approach aligns with checks performed by middleBrick’s BOLA/IDOR and Property Authorization scans, which verify that endpoints properly enforce ownership and that sensitive fields are not trusted from the client.

• How does middleBrick detect insecure design issues with Echo Go and Firestore?

  middleBrick runs parallel security checks including BOLA/IDOR, Property Authorization, and Unsafe Consumption. These scans analyze the unauthenticated attack surface, compare the OpenAPI spec with runtime behavior, and highlight patterns where client-controlled identifiers can lead to unauthorized access in Firestore integrations.

• Does middleBrick fix these Firestore design issues automatically?

  No. middleBrick detects and reports findings with severity, guidance, and references to frameworks such as OWASP API Top 10. It does not modify code, block requests, or patch services. Developers must apply server-side scoping and validation based on the remediation guidance.