1 files changed, 54 insertions, 3 deletions
diff --git a/spec/lib/banzai/filter/syntax_highlight_filter_spec.rb b/spec/lib/banzai/filter/syntax_highlight_filter_spec.rb
index 9f2efa05a01..ef52c572898 100644
--- a/spec/lib/banzai/filter/syntax_highlight_filter_spec.rb
+++ b/spec/lib/banzai/filter/syntax_highlight_filter_spec.rb
@@ -3,35 +3,86 @@ require 'spec_helper'
 describe Banzai::Filter::SyntaxHighlightFilter do
   include FilterSpecHelper
 
+  shared_examples "XSS prevention" do |lang|
+    it "escapes HTML tags" do
+      # This is how a script tag inside a code block is presented to this filter
+      # after Markdown rendering.
+      result = filter(%{<pre lang="#{lang}"><code>&lt;script&gt;alert(1)&lt;/script&gt;</code></pre>})
+
+      expect(result.to_html).not_to include("<script>alert(1)</script>")
+      expect(result.to_html).to include("alert(1)")
+    end
+  end
+
   context "when no language is specified" do
     it "highlights as plaintext" do
       result = filter('<pre><code>def fun end</code></pre>')
+
       expect(result.to_html).to eq('<pre class="code highlight js-syntax-highlight plaintext" lang="plaintext" v-pre="true"><code><span id="LC1" class="line" lang="plaintext">def fun end</span></code></pre>')
     end
+
+    include_examples "XSS prevention", ""
   end
 
   context "when a valid language is specified" do
     it "highlights as that language" do
       result = filter('<pre><code lang="ruby">def fun end</code></pre>')
+
       expect(result.to_html).to eq('<pre class="code highlight js-syntax-highlight ruby" lang="ruby" v-pre="true"><code><span id="LC1" class="line" lang="ruby"><span class="k">def</span> <span class="nf">fun</span> <span class="k">end</span></span></code></pre>')
     end
+
+    include_examples "XSS prevention", "ruby"
   end
 
   context "when an invalid language is specified" do
     it "highlights as plaintext" do
       result = filter('<pre><code lang="gnuplot">This is a test</code></pre>')
+
       expect(result.to_html).to eq('<pre class="code highlight js-syntax-highlight plaintext" lang="plaintext" v-pre="true"><code><span id="LC1" class="line" lang="plaintext">This is a test</span></code></pre>')
     end
+
+    include_examples "XSS prevention", "gnuplot"
   end
 
-  context "when Rouge formatting fails" do
+  context "languages that should be passed through" do
+    %w(math mermaid plantuml).each do |lang|
+      context "when #{lang} is specified" do
+        it "highlights as plaintext but with the correct language attribute and class" do
+          result = filter(%{<pre><code lang="#{lang}">This is a test</code></pre>})
+
+          expect(result.to_html).to eq(%{<pre class="code highlight js-syntax-highlight #{lang}" lang="#{lang}" v-pre="true"><code><span id="LC1" class="line" lang="#{lang}">This is a test</span></code></pre>})
+        end
+
+        include_examples "XSS prevention", lang
+      end
+    end
+  end
+
+  context "when Rouge lexing fails" do
     before do
-      allow_any_instance_of(Rouge::Formatter).to receive(:format).and_raise(StandardError)
+      allow_any_instance_of(Rouge::Lexers::Ruby).to receive(:stream_tokens).and_raise(StandardError)
     end
 
     it "highlights as plaintext" do
       result = filter('<pre><code lang="ruby">This is a test</code></pre>')
-      expect(result.to_html).to eq('<pre class="code highlight js-syntax-highlight" lang="" v-pre="true"><code>This is a test</code></pre>')
+
+      expect(result.to_html).to eq('<pre class="code highlight js-syntax-highlight" lang="" v-pre="true"><code><span id="LC1" class="line" lang="">This is a test</span></code></pre>')
+    end
+
+    include_examples "XSS prevention", "ruby"
+  end
+
+  context "when Rouge lexing fails after a retry" do
+    before do
+      allow_any_instance_of(Rouge::Lexers::PlainText).to receive(:stream_tokens).and_raise(StandardError)
+    end
+
+    it "does not add highlighting classes" do
+      result = filter('<pre><code>This is a test</code></pre>')
+
+      expect(result.to_html).to eq('<pre><code>This is a test</code></pre>')
     end
+
+    include_examples "XSS prevention", "ruby"
   end
 end