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experiment: use loofah attribute scrubber to explore functional drift #136

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experiment: use loofah attribute scrubber to explore functional drift #136

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ff9364e
add failing test
goromlagche Jun 8, 2022
684a020
wip
flavorjones Jun 9, 2022
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1 change: 1 addition & 0 deletions Gemfile
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Original file line number Diff line number Diff line change
Expand Up @@ -5,3 +5,4 @@ gemspec

gem "nokogiri", RUBY_VERSION < "2.1" ? "~> 1.6.0" : ">= 1.7"
gem "activesupport", RUBY_VERSION < "2.2.2" ? "~> 4.2.0" : ">= 5"
gem "loofah", git: "https://github.com/flavorjones/loofah", branch: "flavorjones-scrub-accepts-allowed-attribute-names"
46 changes: 1 addition & 45 deletions lib/rails/html/scrubbers.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -86,10 +86,6 @@ def skip_node?(node)
node.text?
end

def scrub_attribute?(name)
[email protected]?(name)
end

def keep_node?(node)
if @tags
allowed_node?(node)
Expand All @@ -105,58 +101,18 @@ def scrub_node(node)

def scrub_attributes(node)
if @attributes
node.attribute_nodes.each do |attr|
attr.remove if scrub_attribute?(attr.name)
scrub_attribute(node, attr)
end

scrub_css_attribute(node)
Loofah::HTML5::Scrub.scrub_attributes(node, allowed_attribute_names: @attributes)
else
Loofah::HTML5::Scrub.scrub_attributes(node)
end
end

def scrub_css_attribute(node)
if Loofah::HTML5::Scrub.respond_to?(:scrub_css_attribute)
Loofah::HTML5::Scrub.scrub_css_attribute(node)
else
style = node.attributes['style']
style.value = Loofah::HTML5::Scrub.scrub_css(style.value) if style
end
end

def validate!(var, name)
if var && !var.is_a?(Enumerable)
raise ArgumentError, "You should pass :#{name} as an Enumerable"
end
var
end

def scrub_attribute(node, attr_node)
attr_name = if attr_node.namespace
"#{attr_node.namespace.prefix}:#{attr_node.node_name}"
else
attr_node.node_name
end

if Loofah::HTML5::SafeList::ATTR_VAL_IS_URI.include?(attr_name)
# this block lifted nearly verbatim from HTML5 sanitization
val_unescaped = CGI.unescapeHTML(attr_node.value).gsub(Loofah::HTML5::Scrub::CONTROL_CHARACTERS,'').downcase
if val_unescaped =~ /^[a-z0-9][-+.a-z0-9]*:/ && ! Loofah::HTML5::SafeList::ALLOWED_PROTOCOLS.include?(val_unescaped.split(Loofah::HTML5::SafeList::PROTOCOL_SEPARATOR)[0])
attr_node.remove
end
end
if Loofah::HTML5::SafeList::SVG_ATTR_VAL_ALLOWS_REF.include?(attr_name)
attr_node.value = attr_node.value.gsub(/url\s*\(\s*[^#\s][^)]+?\)/m, ' ') if attr_node.value
end
if Loofah::HTML5::SafeList::SVG_ALLOW_LOCAL_HREF.include?(node.name) && attr_name == 'xlink:href' && attr_node.value =~ /^\s*[^#\s].*/m
attr_node.remove
end

node.remove_attribute(attr_node.name) if attr_name == 'src' && attr_node.value !~ /[^[:space:]]/

Loofah::HTML5::Scrub.force_correct_attribute_escaping! node
end
end

# === Rails::Html::TargetScrubber
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10 changes: 10 additions & 0 deletions test/sanitizer_test.rb
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Expand Up @@ -515,6 +515,16 @@ def test_allow_data_attribute_if_requested
assert_equal %(<a data-foo="foo">foo</a>), safe_list_sanitize(text, attributes: ['data-foo'])
end

def test_sanitize_data_protocol
text = "- XSS\"><iframe src=\"data:text/html;base64,PHNjcmlwdD5hbGVydCgnWFNTJyk8L3NjcmlwdD4=\">- XSS\"><iframe src=\"data:application/vnd.wap.xhtml+xml;base64,PHg6c2NyaXB0IHhtbG5zOng9Imh0dHA6Ly93d3cudzMub3JnLzE5OTkveGh0bWwiPmFsZXJ0KGRvY3VtZW50LmRvbWFpbik8L3g6c2NyaXB0Pg==\">"

scope_allowed_tags %w(iframe) do
scope_allowed_attributes %w(src) do
assert_equal %(- XSS\"&gt;<iframe>- XSS\"&gt;<iframe></iframe></iframe>), safe_list_sanitize(text)
end
end
end

def test_uri_escaping_of_href_attr_in_a_tag_in_safe_list_sanitizer
skip if RUBY_VERSION < "2.3"

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