ruby.rails.security.audit.xss.avoid-raw.avoid-raw

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'raw()' bypasses HTML escaping. If external data can reach here, this exposes your application to cross-site scripting (XSS) attacks. If you must do this, construct individual strings and mark them as safe for HTML rendering with html_safe().

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Defintion

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rules:
  - id: avoid-raw
    metadata:
      source-rule-url: https://github.com/presidentbeef/brakeman/blob/main/lib/brakeman/checks/check_cross_site_scripting.rb
      owasp:
        - A07:2017 - Cross-Site Scripting (XSS)
        - A03:2021 - Injection
      cwe:
        - "CWE-79: Improper Neutralization of Input During Web Page Generation
          ('Cross-site Scripting')"
      references:
        - https://api.rubyonrails.org/classes/ActionView/Helpers/OutputSafetyHelper.html#method-i-raw
        - https://www.netsparker.com/blog/web-security/preventing-xss-ruby-on-rails-web-applications/
      category: security
      technology:
        - rails
      cwe2022-top25: true
      cwe2021-top25: true
      subcategory:
        - audit
      likelihood: LOW
      impact: MEDIUM
      confidence: LOW
      license: Commons Clause License Condition v1.0[LGPL-2.1-only]
      vulnerability_class:
        - Cross-Site-Scripting (XSS)
    message: "'raw()' bypasses HTML escaping. If external data can reach here, this
      exposes your application to cross-site scripting (XSS) attacks. If you
      must do this, construct individual strings and mark them as safe for HTML
      rendering with `html_safe()`."
    languages:
      - ruby
    severity: WARNING
    pattern: raw(...)

Examples

avoid-raw.rb

# cf. https://github.com/rails/rails/blob/62d089a4ad0170320b851addf76f7f48a49d68d8/actionview/test/template/output_safety_helper_test.rb

# frozen_string_literal: true

require "abstract_unit"

class OutputSafetyHelperTest < ActionView::TestCase
  tests ActionView::Helpers::OutputSafetyHelper

  def setup
    @string = "hello"
  end

  test "raw returns the safe string" do
    # ruleid: avoid-raw
    result = raw(@string)
    assert_equal @string, result
    assert_predicate result, :html_safe?
  end

  test "raw handles nil values correctly" do
    # ruleid: avoid-raw
    assert_equal "", raw(nil)
  end

  test "safe_join should html_escape any items, including the separator, if they are not html_safe" do
    # ruleid: avoid-raw
    joined = safe_join([raw("<p>foo</p>"), "<p>bar</p>"], "<br />")
    assert_equal "<p>foo</p>&lt;br /&gt;&lt;p&gt;bar&lt;/p&gt;", joined

    # ruleid: avoid-raw
    joined = safe_join([raw("<p>foo</p>"), raw("<p>bar</p>")], raw("<br />"))
    assert_equal "<p>foo</p><br /><p>bar</p>", joined
  end

  test "safe_join should work recursively similarly to Array.join" do
    joined = safe_join(["a", ["b", "c"]], ":")
    assert_equal "a:b:c", joined

    joined = safe_join(['"a"', ["<b>", "<c>"]], " <br/> ")
    assert_equal "&quot;a&quot; &lt;br/&gt; &lt;b&gt; &lt;br/&gt; &lt;c&gt;", joined
  end

  test "safe_join should return the safe string separated by $, when second argument is not passed" do
    default_delimeter = $,

    begin
      $, = nil
      joined = safe_join(["a", "b"])
      assert_equal "ab", joined

      silence_warnings do
        $, = "|"
      end
      joined = safe_join(["a", "b"])
      assert_equal "a|b", joined
    ensure
      $, = default_delimeter
    end
  end
end