diff --git a/lib/rdoc/rdoc.rb b/lib/rdoc/rdoc.rb
index c60e0176090563..f356c368ffa04b 100644
--- a/lib/rdoc/rdoc.rb
+++ b/lib/rdoc/rdoc.rb
@@ -430,7 +430,7 @@ 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 f2cc901283556f..f3228c31e0aed7 100644
--- a/test/rdoc/test_rdoc_rdoc.rb
+++ b/test/rdoc/test_rdoc_rdoc.rb
@@ -426,6 +426,19 @@ def test_remove_unparseable_tags_vim
     end
   end
 
+  def test_remove_unparseable_CVE_2021_31799
+    omit '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'
diff --git a/version.h b/version.h
index 4e5e6f393b4b00..e825e598823ff7 100644
--- a/version.h
+++ b/version.h
@@ -2,7 +2,7 @@
 # define RUBY_VERSION_MINOR RUBY_API_VERSION_MINOR
 #define RUBY_VERSION_TEENY 4
 #define RUBY_RELEASE_DATE RUBY_RELEASE_YEAR_STR"-"RUBY_RELEASE_MONTH_STR"-"RUBY_RELEASE_DAY_STR
-#define RUBY_PATCHLEVEL 187
+#define RUBY_PATCHLEVEL 188
 
 #define RUBY_RELEASE_YEAR 2021
 #define RUBY_RELEASE_MONTH 5