Broken Access Control in Buffalo with Firestore

Broken Access Control (BAC) in a Buffalo application using Google Cloud Firestore typically occurs when authorization checks are missing or incorrectly applied before Firestore operations. Because Firestore security rules are not a substitute for application-level authorization, relying on rules alone while omitting checks in Buffalo leaves sensitive data accessible to unauthorized users.

In Buffalo, HTTP handlers often bind URL parameters or JSON payloads directly to Firestore document IDs or query filters. If these inputs are not validated and scoped to the current user, an attacker can modify the parameter to access another user’s data. For example, changing /users/123/profile to /users/456/profile may return data if the handler performs a direct get without verifying that user 456 belongs to the requester.

Firestore’s rules can allow read/write at collection or document level, but they do not enforce row-level constraints that align with business roles or tenant boundaries. Without explicit checks in Buffalo, an attacker who obtains a valid session token may iterate over IDs or use enumeration techniques to map the data landscape. This maps to OWASP API Top 10 #1 (Broken Object Level Authorization) and can expose PII, financial records, or administrative functions.

The combination is risky because Firestore indexes enable fast queries; an attacker can probe accessible fields via manipulated query parameters. If the handler uses admin SDK credentials (for example, via a service account), Firestore rules may be bypassed entirely, leading to mass data exposure. BAC in this stack is not just about missing rules; it is about missing contextual authorization in the application layer, insecure direct object references, and over-permissive rule sets that appear safe but are not enforced consistently.

middleBrick scans such endpoints during black-box testing, checking for missing authorization, IDOR patterns, and insecure direct object references across the unauthenticated attack surface. Findings align with compliance frameworks including OWASP API Top 10 and SOC2, highlighting the need for explicit, per-request checks before any Firestore operation.

Remediation centers on enforcing authorization in Buffalo handlers, parameter validation, and structuring Firestore rules to support least privilege. Always verify that the authenticated user has ownership or explicit permission before reading, updating, or deleting a document.

Example: a profile endpoint should resolve the user ID from the session, ensure it matches the requested profile ID, and then fetch the document. Avoid using raw IDs from the URL without mapping to the current user context.

// handlers/user_profiles.go
package handlers

import (
    "context"
    "net/http"
    "github.com/gobuffalo/buffalo"
    "cloud.google.com/go/firestore"
    "google.golang.org/api/iterator"
)

func ShowProfile(c buffalo.Context) error {
    ctx := c.Request().Context()
    client, err := firestore.NewClient(ctx, <your-project>)
    if err != nil {
        return c.Render(500, r.JSON(map[string]string{"error": "internal"}))
    }
    defer client.Close()

    // Authenticate and identify the current user via session or token
    userID, ok := c.Session().Get("user_id").(string)
    if !ok || userID == "" {
        return c.Render(401, r.JSON(map[string]string{"error": "unauthorized"}))
    }

    // Use the ID from the session, not from URL parameters, to prevent IDOR
    docID := userID
    docRef := client.Collection("profiles").Doc(docID)
    doc, err := docRef.Get(ctx)
    if err != nil || !doc.Exists() {
        return c.Render(404, r.JSON(map[string]string{"error": "not found"}))
    }

    return c.Render(200, r.JSON(doc.Data()))
}

For list or query endpoints, scope queries to the user’s tenant or role. Do not rely on Firestore rules to filter by user ID; apply the filter in Buffalo before issuing the query.

// handlers/orders.go
package handlers

import (
    "context"
    "net/http"
    "github.com/gobuffalo/buffalo"
    "cloud.google.com/go/firestore"
)

func ListOrders(c buffalo.Context) error {
    ctx := c.Request().Context()
    client, err := firestore.NewClient(ctx, <your-project>)
    if err != nil {
        return c.Render(500, r.JSON(map[string]string{"error": "internal"}))
    }
    defer client.Close()

    userID, ok := c.Session().Get("user_id").(string)
    if !ok || userID == "" {
        return c.Render(401, r.JSON(map[string]string{"error": "unauthorized"}))
    }

    // Scope orders to the current user; do not expose other users’ orders
    iter := client.Collection("orders").
        Where("user_id", "==", userID).
        Limit(50).Documents(ctx)
    defer iter.Stop()

    var orders []map[string]interface{}
    for {
        doc, err := iter.Next()
        if err == iterator.Done {
            break
        }
        if err != nil {
            return c.Render(500, r.JSON(map[string]string{"error": "data"}))
        }
        orders = append(orders, doc.Data())
    }

    return c.Render(200, r.JSON(orders))
}

Firestore security rules should complement these checks, using request.auth.uid to enforce ownership, but they must not replace application-level validation. Combine rule-based constraints with explicit user scoping in handlers to achieve defense in depth. middleBrick’s Pro plan supports continuous monitoring for such misconfigurations, integrating with CI/CD to flag risky rule sets or missing authorization before deployment.