Index: lib/rubygems.rb
===================================================================
--- lib/rubygems.rb	(revision 32241)
+++ lib/rubygems.rb	(working copy)
@@ -452,11 +452,15 @@
   def self.ensure_gem_subdirectories dir = Gem.dir
     require 'fileutils'
 
+    old_umask = File.umask
+    File.umask(old_umask | 022)
     %w[cache doc gems specifications].each do |name|
       subdir = File.join dir, name
       next if File.exist? subdir
       FileUtils.mkdir_p subdir rescue nil # in case of perms issues -- lame
     end
+  ensure
+    File.umask(old_umask)
   end
 
   ##
Index: test/rubygems/test_gem.rb
===================================================================
--- test/rubygems/test_gem.rb	(revision 32241)
+++ test/rubygems/test_gem.rb	(working copy)
@@ -604,6 +604,20 @@
     assert File.directory? File.join(@gemhome, "cache")
   end
 
+  def test_self_ensure_gem_directories_safe_permissions
+    FileUtils.rm_r @gemhome
+    Gem.use_paths @gemhome
+
+    old_umask = File.umask
+    File.umask(0)
+    Gem.ensure_gem_subdirectories @gemhome
+
+    assert_equal 0, File::Stat.new(@gemhome).mode & 022
+    assert_equal 0, File::Stat.new(File.join(@gemhome, "cache")).mode & 022
+  ensure
+    File.umask(old_umask)
+  end
+
   def test_self_ensure_gem_directories_missing_parents
     gemdir = File.join @tempdir, 'a/b/c/gemdir'
     FileUtils.rm_rf File.join(@tempdir, 'a') rescue nil