Fix DOS when rendering issue/MR comments

3 files changed, 12 insertions, 1 deletions

diff --git a/changelogs/unreleased/security-DOS_issue_comments_banzai.yml b/changelogs/unreleased/security-DOS_issue_comments_banzai.yml
new file mode 100644
index 00000000000..2405b1a4f5f
--- /dev/null
+++ b/changelogs/unreleased/security-DOS_issue_comments_banzai.yml
@@ -0,0 +1,5 @@
+---
+title: Fix Denial of Service for comments when rendering issues/MR comments
+merge_request:
+author:
+type: security
diff --git a/lib/banzai/filter/relative_link_filter.rb b/lib/banzai/filter/relative_link_filter.rb
index 199b3533cf4..cdf97e75491 100644
--- a/lib/banzai/filter/relative_link_filter.rb
+++ b/lib/banzai/filter/relative_link_filter.rb
@@ -100,7 +100,7 @@ module Banzai
       end
 
       def relative_file_path(uri)
-        path = Addressable::URI.unescape(uri.path)
+        path = Addressable::URI.unescape(uri.path).delete("\0")
         request_path = Addressable::URI.unescape(context[:requested_path])
         nested_path = build_relative_path(path, request_path)
         file_exists?(nested_path) ? nested_path : path
diff --git a/spec/lib/banzai/filter/relative_link_filter_spec.rb b/spec/lib/banzai/filter/relative_link_filter_spec.rb
index dad0a5535c0..f49c4e3586c 100644
--- a/spec/lib/banzai/filter/relative_link_filter_spec.rb
+++ b/spec/lib/banzai/filter/relative_link_filter_spec.rb
@@ -83,6 +83,12 @@ describe Banzai::Filter::RelativeLinkFilter do
     expect { filter(act) }.not_to raise_error
   end
 
+
+  it 'does not explode with an escaped null byte' do	
+    act = link("/%00")
+    expect { filter(act) }.not_to raise_error
+  end
+
   it 'does not raise an exception with a space in the path' do
     act = link("/uploads/d18213acd3732630991986120e167e3d/Landscape_8.jpg  \nBut here's some more unexpected text :smile:)")
     expect { filter(act) }.not_to raise_error