commit fe3c49c9baeeab58304ede915b7edd18ecf360fc
Author: usa <usa@b2dd03c8-39d4-4d8f-98ff-823fe69b080e>
Date:   Sat Jul 3 17:10:28 2021 +0000

    merge revision(s) b1c73f23,c9ab8fe2: [Backport #17877]
    
            [ruby/rdoc] Use File.open to fix the OS Command Injection vulnerability in CVE-2021-31799
    
            https://github.com/ruby/rdoc/commit/a7f5d6ab88
    
            The test for command injection on Unix platforms should be omitted on Windows
    
    
    git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_6@67947 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

diff --git a/lib/rdoc/rdoc.rb b/lib/rdoc/rdoc.rb
index ca2c1abefd..46aace7839 100644
--- a/lib/rdoc/rdoc.rb
+++ b/lib/rdoc/rdoc.rb
@@ -436,7 +436,7 @@ def remove_unparseable files
     files.reject do |file|
       file =~ /\.(?:class|eps|erb|scpt\.txt|svg|ttf|yml)$/i or
         (file =~ /tags$/i and
-         open(file, 'rb') { |io|
+         File.open(file, 'rb') { |io|
            io.read(100) =~ /\A(\f\n[^,]+,\d+$|!_TAG_)/
          })
     end
diff --git a/test/rdoc/test_rdoc_rdoc.rb b/test/rdoc/test_rdoc_rdoc.rb
index 3bce54b243..123b1a4f87 100644
--- a/test/rdoc/test_rdoc_rdoc.rb
+++ b/test/rdoc/test_rdoc_rdoc.rb
@@ -366,6 +366,18 @@ def test_remove_unparseable_tags_vim
     end
   end
 
+  def test_remove_unparseable_CVE_2021_31799
+    skip 'for Un*x platforms' if Gem.win_platform?
+    temp_dir do
+      file_list = ['| touch evil.txt && echo tags']
+      file_list.each do |f|
+        FileUtils.touch f
+      end
+      assert_equal file_list, @rdoc.remove_unparseable(file_list)
+      assert_equal file_list, Dir.children('.')
+    end
+  end
+
   def test_setup_output_dir
     Dir.mktmpdir {|d|
       path = File.join d, 'testdir'