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# encoding: utf-8
require 'set'
class Sanitize; module Transformers; class CleanElement
# Matches a valid HTML5 data attribute name. The unicode ranges included here
# are a conservative subset of the full range of characters that are
# technically allowed, with the intent of matching the most common characters
# used in data attribute names while excluding uncommon or potentially
# misleading characters, or characters with the potential to be normalized
# into unsafe or confusing forms.
#
# If you need data attr names with characters that aren't included here (such
# as combining marks, full-width characters, or CJK), please consider creating
# a custom transformer to validate attributes according to your needs.
#
# http://www.whatwg.org/specs/web-apps/current-work/multipage/elements.html#embedding-custom-non-visible-data-with-the-data-*-attributes
REGEX_DATA_ATTR = /\Adata-(?!xml)[a-z_][\w.\u00E0-\u00F6\u00F8-\u017F\u01DD-\u02AF-]*\z/u
# Attributes that need additional escaping on `<a>` elements due to unsafe
# libxml2 behavior.
UNSAFE_LIBXML_ATTRS_A = Set.new(%w[
name
])
# Attributes that need additional escaping on all elements due to unsafe
# libxml2 behavior.
UNSAFE_LIBXML_ATTRS_GLOBAL = Set.new(%w[
action
href
src
])
# Mapping of original characters to escape sequences for characters that
# should be escaped in attributes affected by unsafe libxml2 behavior.
UNSAFE_LIBXML_ESCAPE_CHARS = {
' ' => '%20',
'"' => '%22'
}
# Regex that matches any single character that needs to be escaped in
# attributes affected by unsafe libxml2 behavior.
UNSAFE_LIBXML_ESCAPE_REGEX = /[ "]/
def initialize(config)
@add_attributes = config[:add_attributes]
@attributes = config[:attributes].dup
@elements = config[:elements]
@protocols = config[:protocols]
@remove_all_contents = false
@remove_element_contents = Set.new
@whitespace_elements = {}
@attributes.each do |element_name, attrs|
unless element_name == :all
@attributes[element_name] = Set.new(attrs).merge(@attributes[:all] || [])
end
end
# Backcompat: if :whitespace_elements is a Set, convert it to a hash.
if config[:whitespace_elements].is_a?(Set)
config[:whitespace_elements].each do |element|
@whitespace_elements[element] = {:before => ' ', :after => ' '}
end
else
@whitespace_elements = config[:whitespace_elements]
end
if config[:remove_contents].is_a?(Enumerable)
@remove_element_contents.merge(config[:remove_contents].map(&:to_s))
else
@remove_all_contents = !!config[:remove_contents]
end
end
def call(env)
node = env[:node]
return if node.type != Nokogiri::XML::Node::ELEMENT_NODE || env[:is_whitelisted]
name = env[:node_name]
# Delete any element that isn't in the config whitelist, unless the node has
# already been deleted from the document.
#
# It's important that we not try to reparent the children of a node that has
# already been deleted, since that seems to trigger a memory leak in
# Nokogiri.
unless @elements.include?(name) || node.parent.nil?
# Elements like br, div, p, etc. need to be replaced with whitespace in
# order to preserve readability.
if @whitespace_elements.include?(name)
node.add_previous_sibling(Nokogiri::XML::Text.new(@whitespace_elements[name][:before].to_s, node.document))
unless node.children.empty?
node.add_next_sibling(Nokogiri::XML::Text.new(@whitespace_elements[name][:after].to_s, node.document))
end
end
unless node.children.empty?
unless @remove_all_contents || @remove_element_contents.include?(name)
node.add_previous_sibling(node.children)
end
end
node.unlink
return
end
attr_whitelist = @attributes[name] || @attributes[:all]
if attr_whitelist.nil?
# Delete all attributes from elements with no whitelisted attributes.
node.attribute_nodes.each {|attr| attr.unlink }
else
allow_data_attributes = attr_whitelist.include?(:data)
# Delete any attribute that isn't allowed on this element.
node.attribute_nodes.each do |attr|
attr_name = attr.name.downcase
unless attr_whitelist.include?(attr_name)
# The attribute isn't whitelisted.
if allow_data_attributes && attr_name.start_with?('data-')
# Arbitrary data attributes are allowed. If this is a data
# attribute, continue.
next if attr_name =~ REGEX_DATA_ATTR
end
# Either the attribute isn't a data attribute or arbitrary data
# attributes aren't allowed. Remove the attribute.
attr.unlink
next
end
# The attribute is whitelisted.
# Remove any attributes that use unacceptable protocols.
if @protocols.include?(name) && @protocols[name].include?(attr_name)
attr_protocols = @protocols[name][attr_name]
if attr.value =~ REGEX_PROTOCOL
unless attr_protocols.include?($1.downcase)
attr.unlink
next
end
else
unless attr_protocols.include?(:relative)
attr.unlink
next
end
end
# Leading and trailing whitespace around URLs is ignored at parse
# time. Stripping it here prevents it from being escaped by the
# libxml2 workaround below.
attr.value = attr.value.strip
end
# libxml2 >= 2.9.2 doesn't escape comments within some attributes, in an
# attempt to preserve server-side includes. This can result in XSS since
# an unescaped double quote can allow an attacker to inject a
# non-whitelisted attribute.
#
# Sanitize works around this by implementing its own escaping for
# affected attributes, some of which can exist on any element and some
# of which can only exist on `<a>` elements.
#
# The relevant libxml2 code is here:
# <https://github.com/GNOME/libxml2/commit/960f0e275616cadc29671a218d7fb9b69eb35588>
if UNSAFE_LIBXML_ATTRS_GLOBAL.include?(attr_name) ||
(name == 'a' && UNSAFE_LIBXML_ATTRS_A.include?(attr_name))
attr.value = attr.value.gsub(UNSAFE_LIBXML_ESCAPE_REGEX, UNSAFE_LIBXML_ESCAPE_CHARS)
end
end
end
# Add required attributes.
if @add_attributes.include?(name)
@add_attributes[name].each {|key, val| node[key] = val }
end
end
end; end; end
|
