Broken Access Control in Echo Go with Firestore

Broken Access Control occurs when API endpoints fail to enforce proper authorization checks, allowing one user to act on another user’s resources. Using the Echo Go web framework with Google Cloud Firestore can unintentionally amplify this risk if authorization logic is incomplete or inconsistent between the application layer and Firestore security rules.

In Echo Go, developers often bind path parameters (e.g., user IDs) directly to handlers and then perform Firestore reads or writes based on those parameters. If the handler does not validate that the authenticated subject is allowed to access or modify the requested document, an attacker can tamper with identifiers (e.g., changing /users/123/profile to /users/456/profile) and gain unauthorized access. This is a classic BOLA/IDOR pattern.

Firestore’s security rules are evaluated independently of application code. If rules are permissive (e.g., allowing read/write when a request is authenticated but not scoped to the user’s own documents), an attacker can exploit weak rules even when Echo Go enforces checks inconsistently. For example, a rule like allow read, write: if request.auth != null; grants broad access, whereas a more restrictive rule should scope to request.auth.uid and the document’s owner UID.

Additionally, Firestore documents often contain references to user roles or permissions. If Echo Go does not re-validate these claims on each request and relies only on client-supplied data, attackers can escalate privileges by modifying role fields or exploiting overly permissive Firestore rules. The combination of Echo Go routing, Firestore document ownership, and weak or missing authorization checks across both layers creates a high-risk scenario for Broken Access Control.

Remediation requires consistent authorization checks in Echo Go handlers and secure Firestore security rules that scope access to the authenticated user’s data. Below are concrete, realistic code examples.

Echo Go handler with Firestore ownership check

// GET /users/:uid/profile — ensure the requesting user can only access their own profile
func GetProfile(c echo.Context) error {
    uid := c.Param("uid")
    // Authenticated subject from middleware; do not trust the URL parameter alone
    subjectID, exists := c.Get("user_id").(string)
    if !exists {
        return c.JSON(http.StatusUnauthorized, map[string]string{"error": "unauthorized"})
    }
    // Enforce ownership: subject must match the requested UID
    if subjectID != uid {
        return c.JSON(http.StatusForbidden, map[string]string{"error": "access denied"})
    }
    ctx := c.Request().Context()
    client, err := firestore.NewClient(ctx, "your-project-id")
    if err != nil {
        return c.JSON(http.StatusInternalServerError, map[string]string{"error": "server error"})
    }
    defer client.Close()
    docRef := client.Collection("users").Doc(uid)
    docSnap, err := docRef.Get(ctx)
    if err != nil || !docSnap.Exists() {
        return c.JSON(http.StatusNotFound, map[string]string{"error": "not found"})
    }
    return c.JSON(http.StatusOK, docSnap.Data())
}

Firestore security rules scoped to authenticated user

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    // Users can only read/write their own document
    match /users/{userId} {
      allow read, write: if request.auth != null && request.auth.uid == userId;
    }
    // More restrictive rule example: only allow creation if owner UID matches
    match /posts/{postId} {
      allow create: if request.auth != null && request.auth.uid == request.resource.data.user_id;
      allow read, update, delete: if request.auth != null && request.auth.uid == resource.data.user_id;
    }
  }
}

Validate roles server-side

If role-based access is required, store roles in Firestore and re-validate on each request rather than trusting client input. Example check in Echo Go:

func AdminEndpoint(c echo.Context) error {
    subjectID, exists := c.Get("user_id").(string)
    if !exists {
        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": "server error"})
    }
    defer client.Close()
    userDoc, err := client.Collection("users").Doc(subjectID).Get(ctx)
    if err != nil || !userDoc.Exists {
        return c.JSON(http.StatusForbidden, map[string]string{"error": "access denied"})
    }
    var data struct {
        Role string `firestore:"role"`
    }
    if err := userDoc.DataTo(&data); err != nil {
        return c.JSON(http.StatusInternalServerError, map[string]string{"error": "server error"})
    }
    if data.Role != "admin" {
        return c.JSON(http.StatusForbidden, map[string]string{"error": "insufficient permissions"})
    }
    // Proceed with admin action
    return c.JSON(http.StatusOK, map[string]string{"status": "ok"})
}

By combining Echo Go route handling with strict Firestore security rules and server-side re-validation, you reduce the attack surface for Broken Access Control. These practices align with findings commonly reported by scanners and help meet compliance mappings to frameworks such as OWASP API Top 10 A01:2023 and SOC2 controls.