Merge branch 'security-60143-patch-additional-xss-vector-in-wikis' into 'master'

Extract SanitizeNodeLink and apply to WikiLinkFilter

See merge request gitlab/gitlabhq!3143

changelogs/unreleased/security-60143-patch-additional-xss-vector-in-wikis.yml

+---
+title: Patch XSS issue in wiki links
+merge_request:
+author:
+type: security

lib/banzai/filter/autolink_filter.rb

@@ -18,6 +18,7 @@ module Banzai
     #
     class AutolinkFilter < HTML::Pipeline::Filter
       include ActionView::Helpers::TagHelper
+      include Gitlab::Utils::SanitizeNodeLink
 
       # Pattern to match text that should be autolinked.
       #
@@ -72,19 +73,11 @@ module Banzai
 
       private
 
-      # Return true if any of the UNSAFE_PROTOCOLS strings are included in the URI scheme
-      def contains_unsafe?(scheme)
-        return false unless scheme
-
-        scheme = scheme.strip.downcase
-        Banzai::Filter::SanitizationFilter::UNSAFE_PROTOCOLS.any? { |protocol| scheme.include?(protocol) }
-      end
-
       def autolink_match(match)
         # start by stripping out dangerous links
         begin
           uri = Addressable::URI.parse(match)
-          return match if contains_unsafe?(uri.scheme)
+          return match unless safe_protocol?(uri.scheme)
         rescue Addressable::URI::InvalidURIError
           return match
         end

lib/banzai/filter/base_sanitization_filter.rb

@@ -11,6 +11,7 @@ module Banzai
     # Extends HTML::Pipeline::SanitizationFilter with common rules.
     class BaseSanitizationFilter < HTML::Pipeline::SanitizationFilter
       include Gitlab::Utils::StrongMemoize
+      extend Gitlab::Utils::SanitizeNodeLink
 
       UNSAFE_PROTOCOLS = %w(data javascript vbscript).freeze
 
@@ -40,7 +41,7 @@ module Banzai
           # Allow any protocol in `a` elements
           # and then remove links with unsafe protocols
           whitelist[:protocols].delete('a')
-          whitelist[:transformers].push(self.class.remove_unsafe_links)
+          whitelist[:transformers].push(self.class.method(:remove_unsafe_links))
 
           # Remove `rel` attribute from `a` elements
           whitelist[:transformers].push(self.class.remove_rel)
@@ -54,35 +55,6 @@ module Banzai
       end
 
       class << self
-        def remove_unsafe_links
-          lambda do |env|
-            node = env[:node]
-
-            return unless node.name == 'a'
-            return unless node.has_attribute?('href')
-
-            begin
-              node['href'] = node['href'].strip
-              uri = Addressable::URI.parse(node['href'])
-
-              return unless uri.scheme
-
-              # Remove all invalid scheme characters before checking against the
-              # list of unsafe protocols.
-              #
-              # See https://tools.ietf.org/html/rfc3986#section-3.1
-              scheme = uri.scheme
-                           .strip
-                           .downcase
-                           .gsub(/[^A-Za-z0-9\+\.\-]+/, '')
-
-              node.remove_attribute('href') if UNSAFE_PROTOCOLS.include?(scheme)
-            rescue Addressable::URI::InvalidURIError
-              node.remove_attribute('href')
-            end
-          end
-        end
-
         def remove_rel
           lambda do |env|
             if env[:node_name] == 'a'

lib/banzai/filter/wiki_link_filter.rb

@@ -8,15 +8,19 @@ module Banzai
     # Context options:
     #   :project_wiki
     class WikiLinkFilter < HTML::Pipeline::Filter
+      include Gitlab::Utils::SanitizeNodeLink
+
       def call
         return doc unless project_wiki?
 
-        doc.search('a:not(.gfm)').each { |el| process_link_attr(el.attribute('href')) }
-        doc.search('video').each { |el| process_link_attr(el.attribute('src')) }
+        doc.search('a:not(.gfm)').each { |el| process_link(el.attribute('href'), el) }
+
+        doc.search('video').each { |el| process_link(el.attribute('src'), el) }
+
         doc.search('img').each do |el|
           attr = el.attribute('data-src') || el.attribute('src')
 
-          process_link_attr(attr)
+          process_link(attr, el)
         end
 
         doc
@@ -24,6 +28,11 @@ module Banzai
 
       protected
 
+      def process_link(link_attr, node)
+        process_link_attr(link_attr)
+        remove_unsafe_links({ node: node }, remove_invalid_links: false)
+      end
+
       def project_wiki?
         !context[:project_wiki].nil?
       end

lib/banzai/filter/wiki_link_filter/rewriter.rb

@@ -4,8 +4,6 @@ module Banzai
   module Filter
     class WikiLinkFilter < HTML::Pipeline::Filter
       class Rewriter
-        UNSAFE_SLUG_REGEXES = [/\Ajavascript:/i].freeze
-
         def initialize(link_string, wiki:, slug:)
           @uri = Addressable::URI.parse(link_string)
           @wiki_base_path = wiki && wiki.wiki_base_path
@@ -37,8 +35,6 @@ module Banzai
 
         # Of the form `./link`, `../link`, or similar
         def apply_hierarchical_link_rules!
-          return if slug_considered_unsafe?
-
           @uri = Addressable::URI.join(@slug, @uri) if @uri.to_s[0] == '.'
         end
 
@@ -58,10 +54,6 @@ module Banzai
         def repository_upload?
           @uri.relative? && @uri.path.starts_with?(Wikis::CreateAttachmentService::ATTACHMENT_PATH)
         end
-
-        def slug_considered_unsafe?
-          UNSAFE_SLUG_REGEXES.any? { |r| r.match?(@slug) }
-        end
       end
     end
   end

lib/gitlab/utils/sanitize_node_link.rb

+# frozen_string_literal: true
+
+require_dependency 'gitlab/utils'
+
+module Gitlab
+  module Utils
+    module SanitizeNodeLink
+      UNSAFE_PROTOCOLS  = %w(data javascript vbscript).freeze
+      ATTRS_TO_SANITIZE = %w(href src data-src).freeze
+
+      def remove_unsafe_links(env, remove_invalid_links: true)
+        node = env[:node]
+
+        sanitize_node(node: node, remove_invalid_links: remove_invalid_links)
+
+        # HTML entities such as <video></video> have scannable attrs in
+        #   children elements, which also need to be sanitized.
+        #
+        node.children.each do |child_node|
+          sanitize_node(node: child_node, remove_invalid_links: remove_invalid_links)
+        end
+      end
+
+      # Remove all invalid scheme characters before checking against the
+      # list of unsafe protocols.
+      #
+      # See https://tools.ietf.org/html/rfc3986#section-3.1
+      #
+      def safe_protocol?(scheme)
+        return false unless scheme
+
+        scheme = scheme
+          .strip
+          .downcase
+          .gsub(/[^A-Za-z\+\.\-]+/, '')
+
+        UNSAFE_PROTOCOLS.none?(scheme)
+      end
+
+      private
+
+      def sanitize_node(node:, remove_invalid_links: true)
+        ATTRS_TO_SANITIZE.each do |attr|
+          next unless node.has_attribute?(attr)
+
+          begin
+            node[attr] = node[attr].strip
+            uri = Addressable::URI.parse(node[attr])
+
+            next unless uri.scheme
+            next if safe_protocol?(uri.scheme)
+
+            node.remove_attribute(attr)
+          rescue Addressable::URI::InvalidURIError
+            node.remove_attribute(attr) if remove_invalid_links
+          end
+        end
+      end
+    end
+  end
+end

spec/lib/banzai/filter/wiki_link_filter_spec.rb

@@ -70,47 +70,5 @@ describe Banzai::Filter::WikiLinkFilter do
         expect(filtered_link.attribute('href').value).to eq(invalid_link)
       end
     end
-
-    context "when the slug is deemed unsafe or invalid" do
-      let(:link) { "alert(1);" }
-
-      invalid_slugs = [
-        "javascript:",
-        "JaVaScRiPt:",
-        "\u0001java\u0003script:",
-        "javascript    :",
-        "javascript:    ",
-        "javascript    :   ",
-        ":javascript:",
-        "javascript:",
-        "javascript:",
-        "javascript:",
-        "javascript:",
-        "java\0script:",
-        "   javascript:"
-        ]
-
-      invalid_slugs.each do |slug|
-        context "with the slug #{slug}" do
-          it "doesn't rewrite a (.) relative link" do
-            filtered_link = filter(
-              "<a href='.#{link}'>Link</a>",
-              project_wiki: wiki,
-              page_slug: slug).children[0]
-
-            expect(filtered_link.attribute('href').value).not_to include(slug)
-          end
-
-          it "doesn't rewrite a (..) relative link" do
-            filtered_link = filter(
-              "<a href='..#{link}'>Link</a>",
-              project_wiki: wiki,
-              page_slug: slug).children[0]
-
-            expect(filtered_link.attribute('href').value).not_to include(slug)
-          end
-        end
-      end
-    end
   end
 end

spec/lib/banzai/pipeline/wiki_pipeline_spec.rb

@@ -177,6 +177,85 @@ describe Banzai::Pipeline::WikiPipeline do
         end
       end
     end
+
+    describe "checking slug validity when assembling links" do
+      context "with a valid slug" do
+        let(:valid_slug) { "http://example.com" }
+
+        it "includes the slug in a (.) relative link" do
+          output = described_class.to_html(
+            "[Link](./alert(1);)",
+            project: project,
+            project_wiki: project_wiki,
+            page_slug: valid_slug
+          )
+
+          expect(output).to include(valid_slug)
+        end
+
+        it "includeds the slug in a (..) relative link" do
+          output = described_class.to_html(
+            "[Link](../alert(1);)",
+            project: project,
+            project_wiki: project_wiki,
+            page_slug: valid_slug
+          )
+
+          expect(output).to include(valid_slug)
+        end
+      end
+
+      context "when the slug is deemed unsafe or invalid" do
+        invalid_slugs = [
+          "javascript:",
+          "JaVaScRiPt:",
+          "\u0001java\u0003script:",
+          "javascript    :",
+          "javascript:    ",
+          "javascript    :   ",
+          ":javascript:",
+          "javascript:",
+          "javascript:",
+          "javascript:",
+          "javascript:",
+          "java\0script:",
+          "   javascript:"
+        ]
+
+        invalid_js_links = [
+          "alert(1);",
+          "alert(document.location);"
+        ]
+
+        invalid_slugs.each do |slug|
+          context "with the invalid slug #{slug}" do
+            invalid_js_links.each do |link|
+              it "doesn't include a prohibited slug in a (.) relative link '#{link}'" do
+                output = described_class.to_html(
+                  "[Link](./#{link})",
+                  project: project,
+                  project_wiki: project_wiki,
+                  page_slug: slug
+                )
+
+                expect(output).not_to include(slug)
+              end
+
+              it "doesn't include a prohibited slug in a (..) relative link '#{link}'" do
+                output = described_class.to_html(
+                  "[Link](../#{link})",
+                  project: project,
+                  project_wiki: project_wiki,
+                  page_slug: slug
+                )
+
+                expect(output).not_to include(slug)
+              end
+            end
+          end
+        end
+      end
+    end
   end
 
   describe 'videos' do

spec/lib/gitlab/utils/sanitize_node_link_spec.rb

+require 'spec_helper'
+
+describe Gitlab::Utils::SanitizeNodeLink do
+  let(:klass) do
+    struct = Struct.new(:value)
+    struct.include(described_class)
+
+    struct
+  end
+
+  subject(:object) { klass.new(:value) }
+
+  invalid_schemes = [
+    "javascript:",
+    "JaVaScRiPt:",
+    "\u0001java\u0003script:",
+    "javascript    :",
+    "javascript:    ",
+    "javascript    :   ",
+    ":javascript:",
+    "javascript:",
+    "javascript:",
+    "   javascript:"
+  ]
+
+  invalid_schemes.each do |scheme|
+    context "with the scheme: #{scheme}" do
+      describe "#remove_unsafe_links" do
+        tags = {
+          a: {
+            doc: HTML::Pipeline.parse("<a href='#{scheme}alert(1);'>foo</a>"),
+            attr: "href",
+            node_to_check: -> (doc) { doc.children.first }
+          },
+          img: {
+            doc: HTML::Pipeline.parse("<img src='#{scheme}alert(1);'>"),
+            attr: "src",
+            node_to_check: -> (doc) { doc.children.first }
+          },
+          video: {
+            doc: HTML::Pipeline.parse("<video><source src='#{scheme}alert(1);'></video>"),
+            attr: "src",
+            node_to_check: -> (doc) { doc.children.first.children.filter("source").first }
+          }
+        }
+
+        tags.each do |tag, opts|
+          context "<#{tag}> tags" do
+            it "removes the unsafe link" do
+              node = opts[:node_to_check].call(opts[:doc])
+
+              expect { object.remove_unsafe_links({ node: node }, remove_invalid_links: true) }
+                .to change { node[opts[:attr]] }
+
+              expect(node[opts[:attr]]).to be_blank
+            end
+          end
+        end
+      end
+
+      describe "#safe_protocol?" do
+        let(:doc) { HTML::Pipeline.parse("<a href='#{scheme}alert(1);'>foo</a>") }
+        let(:node) { doc.children.first }
+        let(:uri) { Addressable::URI.parse(node['href'])}
+
+        it "returns false" do
+          expect(object.safe_protocol?(scheme)).to be_falsy
+        end
+      end
+    end
+  end
+end