Clickjacking in Buffalo with Firestore

Clickjacking is a client-side attack where an attacker tricks a user into interacting with a hidden or disguised UI element, often by loading a target page inside an invisible iframe. When a Buffalo application uses Cloud Firestore as a backend, the combination of server-rendered HTML and Firestore-driven data flows can expose surfaces that are vulnerable if framing protections are missing.

Buffalo does not automatically set anti-framing headers, and if a view embeds Firestore-backed data in iframes or otherwise exposes interactive endpoints without X-Frame-Options or Content-Security-Policy (CSP) frame-ancestors, an attacker can embed the page and capture actions such as creating or updating documents. For example, a page that renders a Firestore document edit form and is served without restrictive headers can be framed; an invisible overlay can cause unintended writes when the user believes they are interacting with the visible page.

Because Firestore security rules operate on data and not UI framing, they do not prevent clickjacking. A rule that permits read/write based on authentication (e.g., allowing a user to update their own profile) does not stop an attacker from loading that edit form in a frame and luring the user into submitting it. The request will include the user’s session cookie or token, and Firestore will evaluate the rules as satisfied, leading to unauthorized updates. The risk is compounded if the application exposes Firestore document IDs in URLs or forms without additional authorization checks on each request, and if UI state is derived directly from Firestore without anti-CSRF tokens or same-site cookie attributes.

Additionally, if your Buffalo app serves an API that returns Firestore data to frontend JavaScript that is itself embeddable, an attacker can craft a page that loads your endpoint and overlays controls on top of the retrieved data. Since Firestore does not provide built-in UI protection, the server must enforce framing defenses and include anti-CSRF measures for any state-changing operations that rely on Firestore writes.

Remediation focuses on HTTP headers, CSP, server-side authorization, and anti-CSRF tokens. Firestore security rules remain necessary for data validation and access control but do not address framing.

• Set anti-framing headers in Buffalo to prevent your pages from being embedded:

# In your Buffalo middleware stack (e.g., in app/middleware.ex)
plug Plug.ResponseHeaders,
  "X-Frame-Options" => "DENY",
  "Content-Security-Policy" => "frame-ancestors 'self';"

• Use same-site cookies and anti-CSRF tokens for any form that writes to Firestore. For forms that perform Firestore document updates, include a server-generated token and verify it on submit:

# In a form helper (e.g., within a buffalo/render call)
<form action="/profile/update" method="POST">
  <input type="hidden" name="csrf_token" value="<%= @csrf_token %>">
  <input type="text" name="display_name" value="<%= @user.display_name %>">
  <button type="submit">Save</button>
</form>

# In your handler that processes the update
post "/profile/update" do
  csrf_token = param(conn, "csrf_token")
  unless csrf_token == get_session(conn, :csrf_token) do
    conn
    |> put_status(:forbidden)
    |> text("Invalid CSRF token")
    |> halt()
  end

  uid = conn.assigns.current_user.id
  updates = param(conn, "display_name")

  # Assume Firestore client is available as conn.assigns.firestore
  case Firestore.update_document(conn.assigns.firestore, "users/#{uid}", %{"displayName" => updates}) do
    {:ok, _} -> redirect(conn, Routes.profile_path(conn, :show))
    {:error, reason} -> render(conn, "error.html", reason: reason)
  end
end

• Apply least-privilege Firestore rules that scope writes to the authenticated user and do not rely on the request origin:

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

• For APIs that return Firestore data to frontend embeds, require explicit authorization for each operation and avoid embedding sensitive write endpoints. If you must serve embeddable widgets, isolate them behind additional checks such as referer validation or CAPTCHA challenges.