Merge branch 'bvl-security-9-1-validate-urls-in-markdown-using-uri'

(security-9-1) Add correct `rel` attributes to external links when rendering markdown

See merge request !2097

4 files changed, 86 insertions, 56 deletions

diff --git a/changelogs/unreleased/bvl-validate-urls-in-markdown-using-uri.yml b/changelogs/unreleased/bvl-validate-urls-in-markdown-using-uri.yml
new file mode 100644
index 00000000000..03c4e531d73
--- /dev/null
+++ b/changelogs/unreleased/bvl-validate-urls-in-markdown-using-uri.yml
@@ -0,0 +1,4 @@
+---
+title: Validate URLs in markdown using URI to detect the host correctly
+merge_request:
+author:
diff --git a/lib/banzai/filter/external_link_filter.rb b/lib/banzai/filter/external_link_filter.rb
index d67d466bce8..7d15a0f6d44 100644
--- a/lib/banzai/filter/external_link_filter.rb
+++ b/lib/banzai/filter/external_link_filter.rb
@@ -2,16 +2,17 @@ module Banzai
   module Filter
     # HTML Filter to modify the attributes of external links
     class ExternalLinkFilter < HTML::Pipeline::Filter
+      SCHEMES = ['http', 'https', nil].freeze
+
       def call
         links.each do |node|
-          href = href_to_lowercase_scheme(node["href"].to_s)
+          uri = uri(node['href'].to_s)
+          next unless uri
 
-          unless node["href"].to_s == href
-            node.set_attribute('href', href)
-          end
+          node.set_attribute('href', uri.to_s)
 
-          if href =~ %r{\A(https?:)?//[^/]} && external_url?(href)
-            node.set_attribute('rel', 'nofollow noreferrer')
+          if SCHEMES.include?(uri.scheme) && external_url?(uri)
+            node.set_attribute('rel', 'nofollow noreferrer noopener')
             node.set_attribute('target', '_blank')
           end
         end
@@ -21,27 +22,26 @@ module Banzai
 
       private
 
+      def uri(href)
+        URI.parse(href)
+      rescue URI::InvalidURIError
+        nil
+      end
+
       def links
         query = 'descendant-or-self::a[@href and not(@href = "")]'
         doc.xpath(query)
       end
 
-      def href_to_lowercase_scheme(href)
-        scheme_match = href.match(/\A(\w+):\/\//)
-
-        if scheme_match
-          scheme_match.to_s.downcase + scheme_match.post_match
-        else
-          href
-        end
-      end
+      def external_url?(uri)
+        # Relative URLs miss a hostname
+        return false unless uri.hostname
 
-      def external_url?(url)
-        !url.start_with?(internal_url)
+        uri.hostname != internal_url.hostname
       end
 
       def internal_url
-        @internal_url ||= Gitlab.config.gitlab.url
+        @internal_url ||= URI.parse(Gitlab.config.gitlab.url)
       end
     end
   end
diff --git a/spec/lib/banzai/filter/external_link_filter_spec.rb b/spec/lib/banzai/filter/external_link_filter_spec.rb
index d9e4525cb28..6f6c215be87 100644
--- a/spec/lib/banzai/filter/external_link_filter_spec.rb
+++ b/spec/lib/banzai/filter/external_link_filter_spec.rb
@@ -1,5 +1,22 @@
 require 'spec_helper'
 
+shared_examples 'an external link with rel attribute' do
+  it 'adds rel="nofollow" to external links' do
+    expect(doc.at_css('a')).to have_attribute('rel')
+    expect(doc.at_css('a')['rel']).to include 'nofollow'
+  end
+
+  it 'adds rel="noreferrer" to external links' do
+    expect(doc.at_css('a')).to have_attribute('rel')
+    expect(doc.at_css('a')['rel']).to include 'noreferrer'
+  end
+
+  it 'adds rel="noopener" to external links' do
+    expect(doc.at_css('a')).to have_attribute('rel')
+    expect(doc.at_css('a')['rel']).to include 'noopener'
+  end
+end
+
 describe Banzai::Filter::ExternalLinkFilter, lib: true do
   include FilterSpecHelper
 
@@ -22,49 +39,51 @@ describe Banzai::Filter::ExternalLinkFilter, lib: true do
   context 'for root links on document' do
     let(:doc) { filter %q(<a href="https://google.com/">Google</a>) }
 
-    it 'adds rel="nofollow" to external links' do
-      expect(doc.at_css('a')).to have_attribute('rel')
-      expect(doc.at_css('a')['rel']).to include 'nofollow'
-    end
-
-    it 'adds rel="noreferrer" to external links' do
-      expect(doc.at_css('a')).to have_attribute('rel')
-      expect(doc.at_css('a')['rel']).to include 'noreferrer'
-    end
+    it_behaves_like 'an external link with rel attribute'
   end
 
   context 'for nested links on document' do
     let(:doc) { filter %q(<p><a href="https://google.com/">Google</a></p>) }
 
-    it 'adds rel="nofollow" to external links' do
-      expect(doc.at_css('a')).to have_attribute('rel')
-      expect(doc.at_css('a')['rel']).to include 'nofollow'
+    it_behaves_like 'an external link with rel attribute'
+  end
+
+  context 'for invalid urls' do
+    it 'skips broken hrefs' do
+      doc = filter %q(<p><a href="don't crash on broken urls">Google</a></p>)
+      expected = %q(<p><a href="don't%20crash%20on%20broken%20urls">Google</a></p>)
+
+      expect(doc.to_html).to eq(expected)
     end
+  end
+
+  context 'for links with a username' do
+    context 'with a valid username' do
+      let(:doc) { filter %q(<a href="https://user@google.com/">Google</a>) }
 
-    it 'adds rel="noreferrer" to external links' do
-      expect(doc.at_css('a')).to have_attribute('rel')
-      expect(doc.at_css('a')['rel']).to include 'noreferrer'
+      it_behaves_like 'an external link with rel attribute'
+    end
+
+    context 'with an impersonated username' do
+      let(:internal) { Gitlab.config.gitlab.url }
+
+      let(:doc) { filter %Q(<a href="https://#{internal}@example.com" target="_blank">Reverse Tabnabbing</a>) }
+
+      it_behaves_like 'an external link with rel attribute'
     end
   end
 
   context 'for non-lowercase scheme links' do
-    let(:doc_with_http) { filter %q(<p><a href="httP://google.com/">Google</a></p>) }
-    let(:doc_with_https) { filter %q(<p><a href="hTTpS://google.com/">Google</a></p>) }
-
-    it 'adds rel="nofollow" to external links' do
-      expect(doc_with_http.at_css('a')).to have_attribute('rel')
-      expect(doc_with_https.at_css('a')).to have_attribute('rel')
+    context 'with http' do
+      let(:doc) { filter %q(<p><a href="httP://google.com/">Google</a></p>) }
 
-      expect(doc_with_http.at_css('a')['rel']).to include 'nofollow'
-      expect(doc_with_https.at_css('a')['rel']).to include 'nofollow'
+      it_behaves_like 'an external link with rel attribute'
     end
 
-    it 'adds rel="noreferrer" to external links' do
-      expect(doc_with_http.at_css('a')).to have_attribute('rel')
-      expect(doc_with_https.at_css('a')).to have_attribute('rel')
+    context 'with https' do
+      let(:doc) { filter %q(<p><a href="hTTpS://google.com/">Google</a></p>) }
 
-      expect(doc_with_http.at_css('a')['rel']).to include 'noreferrer'
-      expect(doc_with_https.at_css('a')['rel']).to include 'noreferrer'
+      it_behaves_like 'an external link with rel attribute'
     end
 
     it 'skips internal links' do
@@ -84,14 +103,6 @@ describe Banzai::Filter::ExternalLinkFilter, lib: true do
   context 'for protocol-relative links' do
     let(:doc) { filter %q(<p><a href="//google.com/">Google</a></p>) }
 
-    it 'adds rel="nofollow" to external links' do
-      expect(doc.at_css('a')).to have_attribute('rel')
-      expect(doc.at_css('a')['rel']).to include 'nofollow'
-    end
-
-    it 'adds rel="noreferrer" to external links' do
-      expect(doc.at_css('a')).to have_attribute('rel')
-      expect(doc.at_css('a')['rel']).to include 'noreferrer'
-    end
+    it_behaves_like 'an external link with rel attribute'
   end
 end
diff --git a/spec/lib/gitlab/asciidoc_spec.rb b/spec/lib/gitlab/asciidoc_spec.rb
index f284dd14cec..2c7ebb15fd7 100644
--- a/spec/lib/gitlab/asciidoc_spec.rb
+++ b/spec/lib/gitlab/asciidoc_spec.rb
@@ -25,6 +25,21 @@ module Gitlab
         expect(render(input, context)).to eq(html)
       end
 
+      context "with asciidoc_opts" do
+        it "merges the options with default ones" do
+          expected_asciidoc_opts = {
+              safe: :secure,
+              backend: :gitlab_html5,
+              attributes: described_class::DEFAULT_ADOC_ATTRS
+          }
+
+          expect(Asciidoctor).to receive(:convert)
+            .with(input, expected_asciidoc_opts).and_return(html)
+
+          render(input, context)
+        end
+      end
+
       context "XSS" do
         links = {
           'links' => {
@@ -52,7 +67,7 @@ module Gitlab
         it 'adds the `rel` attribute to the link' do
           output = render('link:https://google.com[Google]', context)
 
-          expect(output).to include('rel="nofollow noreferrer"')
+          expect(output).to include('rel="nofollow noreferrer noopener"')
         end
       end
     end