diff --git a/lib/markdown_renderer.rb b/lib/markdown_renderer.rb
index 97c49685..042b3a2c 100644
--- a/lib/markdown_renderer.rb
+++ b/lib/markdown_renderer.rb
@@ -20,6 +20,7 @@ def header(text, header_level)
   end
 
   def image(url, title, alt_text)
+    url, title, alt_text = [ url, title, alt_text ].map { ERB::Util.html_escape_once(it) }
     %(<a title="#{title}" data-action="lightbox#open:prevent" data-lightbox-target="image" data-lightbox-url-value="#{url}?disposition=attachment" href="#{url}"><img src="#{url}" alt="#{alt_text}"></a>)
   end
 
diff --git a/test/lib/markdown_renderer_test.rb b/test/lib/markdown_renderer_test.rb
index c3ad2119..ca5315cc 100644
--- a/test/lib/markdown_renderer_test.rb
+++ b/test/lib/markdown_renderer_test.rb
@@ -8,4 +8,14 @@ class MarkdownRendererTest < ActiveSupport::TestCase
     assert_includes content, "id='duplicated-header'"
     assert_includes content, "id='duplicated-header-2'"
   end
+
+  test "it escapes image attributes" do
+    markdown = MarkdownRenderer.build
+    content = markdown.render(%(![a "b" &amp; c](/image.png?a=1&b=2 "x" data-x="y")))
+
+    assert_includes content, %(title="x&quot; data-x=&quot;y")
+    assert_includes content, %(alt="a &quot;b&quot; &amp; c")
+    assert_includes content, %(href="/image.png?a=1&amp;b=2")
+    assert_empty Nokogiri::HTML5.fragment(content).css("[data-x]")
+  end
 end