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SECURITY: Add content-disposition: attachment for SVG uploads
* strip out the href and xlink:href attributes from use element that are _not_ anchors in svgs which can be used for XSS * adding the content-disposition: attachment ensures that uploaded SVGs cannot be opened and executed using the XSS exploit. svgs embedded using an img tag do not suffer from the same exploit
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@ -249,7 +249,7 @@ class UploadsController < ApplicationController
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content_type: MiniMime.lookup_by_filename(upload.original_filename)&.content_type
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}
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if !FileHelper.is_supported_image?(upload.original_filename)
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if !FileHelper.is_inline_image?(upload.original_filename)
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opts[:disposition] = "attachment"
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elsif params[:inline]
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opts[:disposition] = "inline"
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@ -185,9 +185,12 @@ server {
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try_files $uri =404;
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}
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# this allows us to bypass rails
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location ~* \.(gif|png|jpg|jpeg|bmp|tif|tiff|svg|ico|webp)$ {
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location ~* \.(gif|png|jpg|jpeg|bmp|tif|tiff|ico|webp)$ {
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try_files $uri =404;
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}
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# SVG needs an extra header attached
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location ~* \.(svg)$ {
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}
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# thumbnails & optimized images
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location ~ /_?optimized/ {
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try_files $uri =404;
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@ -17,6 +17,10 @@ class FileHelper
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(filename =~ supported_images_regexp).present?
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end
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def self.is_inline_image?(filename)
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(filename =~ inline_images_regexp).present?
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end
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def self.is_supported_media?(filename)
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(filename =~ supported_media_regexp).present?
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end
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@ -136,6 +140,11 @@ class FileHelper
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@@supported_images ||= Set.new %w{jpg jpeg png gif svg ico webp}
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end
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def self.inline_images
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# SVG cannot safely be shown as a document
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@@inline_images ||= supported_images - %w{svg}
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end
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def self.supported_audio
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@@supported_audio ||= Set.new %w{mp3 ogg wav m4a}
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end
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@ -148,6 +157,10 @@ class FileHelper
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@@supported_images_regexp ||= /\.(#{supported_images.to_a.join("|")})$/i
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end
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def self.inline_images_regexp
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@@inline_images_regexp ||= /\.(#{inline_images.to_a.join("|")})$/i
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end
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def self.supported_media_regexp
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media = supported_images | supported_audio | supported_video
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@@supported_media_regexp ||= /\.(#{media.to_a.join("|")})$/i
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@ -54,11 +54,12 @@ module FileStore
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content_type: opts[:content_type].presence || MiniMime.lookup_by_filename(filename)&.content_type
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}
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# add a "content disposition: attachment" header with the original filename
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# for everything but images. audio and video will still stream correctly in
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# HTML players, and when a direct link is provided to any file but an image
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# it will download correctly in the browser.
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if !FileHelper.is_supported_image?(filename)
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# add a "content disposition: attachment" header with the original
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# filename for everything but safe images (not SVG). audio and video will
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# still stream correctly in HTML players, and when a direct link is
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# provided to any file but an image it will download correctly in the
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# browser.
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if !FileHelper.is_inline_image?(filename)
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options[:content_disposition] = ActionDispatch::Http::ContentDisposition.format(
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disposition: "attachment", filename: filename
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)
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@ -232,6 +232,11 @@ module FileStore
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if upload&.secure
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options[:acl] = "private"
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end
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elsif !FileHelper.is_inline_image?(name)
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upload = Upload.find_by(url: "/#{file}")
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options[:content_disposition] = ActionDispatch::Http::ContentDisposition.format(
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disposition: "attachment", filename: upload&.original_filename || name
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)
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end
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etag ||= Digest::MD5.file(path).hexdigest
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@ -278,6 +278,14 @@ class UploadCreator
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doc = Nokogiri::XML(@file)
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doc.xpath(svg_whitelist_xpath).remove
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doc.xpath("//@*[starts-with(name(), 'on')]").remove
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doc.css('use').each do |use_el|
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if use_el.attr('href')
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use_el.remove_attribute('href') unless use_el.attr('href').starts_with?('#')
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end
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if use_el.attr('xlink:href')
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use_el.remove_attribute('xlink:href') unless use_el.attr('xlink:href').starts_with?('#')
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end
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end
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File.write(@file.path, doc.to_s)
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@file.rewind
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end
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