diff --git a/ChangeLog b/ChangeLog
index c2c0d5dfa9..0e2c8b342a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Wed Sep 10 11:39:54 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* hash.c (env_aset, env_has_key, env_assoc, env_has_value),
+	  (env_rassoc, env_key): prohibit tainted strings if $SAFE is
+	  non-zero.  [Bug #9976]
+
 Sat Sep  6 09:10:45 2014  Zachary Scott  <e@zzak.io>
 
 	* lib/rdoc/generator/template/darkfish/js/jquery.js: Backport
diff --git a/hash.c b/hash.c
index 1ca87de1ec..0cb3379236 100644
--- a/hash.c
+++ b/hash.c
@@ -2547,8 +2547,8 @@ env_aset(VALUE obj, VALUE nm, VALUE val)
 	env_delete(obj, nm);
 	return Qnil;
     }
-    StringValue(nm);
-    StringValue(val);
+    SafeStringValue(nm);
+    SafeStringValue(val);
     name = RSTRING_PTR(nm);
     value = RSTRING_PTR(val);
     if (memchr(name, '\0', RSTRING_LEN(nm)))
@@ -3048,7 +3048,8 @@ env_has_key(VALUE env, VALUE key)
     char *s;
 
     rb_secure(4);
-    s = StringValuePtr(key);
+    SafeStringValue(key);
+    s = RSTRING_PTR(key);
     if (memchr(s, '\0', RSTRING_LEN(key)))
 	rb_raise(rb_eArgError, "bad environment variable name");
     if (getenv(s)) return Qtrue;
@@ -3068,7 +3069,8 @@ env_assoc(VALUE env, VALUE key)
     char *s, *e;
 
     rb_secure(4);
-    s = StringValuePtr(key);
+    SafeStringValue(key);
+    s = RSTRING_PTR(key);
     if (memchr(s, '\0', RSTRING_LEN(key)))
 	rb_raise(rb_eArgError, "bad environment variable name");
     e = getenv(s);
@@ -3091,6 +3093,7 @@ env_has_value(VALUE dmy, VALUE obj)
     rb_secure(4);
     obj = rb_check_string_type(obj);
     if (NIL_P(obj)) return Qnil;
+    rb_check_safe_obj(obj);
     env = GET_ENVIRON(environ);
     while (*env) {
 	char *s = strchr(*env, '=');
@@ -3122,6 +3125,7 @@ env_rassoc(VALUE dmy, VALUE obj)
     rb_secure(4);
     obj = rb_check_string_type(obj);
     if (NIL_P(obj)) return Qnil;
+    rb_check_safe_obj(obj);
     env = GET_ENVIRON(environ);
     while (*env) {
 	char *s = strchr(*env, '=');
@@ -3153,7 +3157,7 @@ env_key(VALUE dmy, VALUE value)
     VALUE str;
 
     rb_secure(4);
-    StringValue(value);
+    SafeStringValue(value);
     env = GET_ENVIRON(environ);
     while (*env) {
 	char *s = strchr(*env, '=');
diff --git a/test/ruby/test_env.rb b/test/ruby/test_env.rb
index 98357ba201..9c97adeb82 100644
--- a/test/ruby/test_env.rb
+++ b/test/ruby/test_env.rb
@@ -448,4 +448,85 @@ class TestEnv < Test::Unit::TestCase
       end;
     end
   end
+
+  def test_taint_aref
+    assert_raise(SecurityError) do
+      proc do
+        $SAFE = 2
+        ENV["FOO".taint]
+      end.call
+    end
+  end
+
+  def test_taint_fetch
+    assert_raise(SecurityError) do
+      proc do
+        $SAFE = 2
+        ENV.fetch("FOO".taint)
+      end.call
+    end
+  end
+
+  def test_taint_assoc
+    assert_raise(SecurityError) do
+      proc do
+        $SAFE = 2
+        ENV.assoc("FOO".taint)
+      end.call
+    end
+  end
+
+  def test_taint_rassoc
+    assert_raise(SecurityError) do
+      proc do
+        $SAFE = 2
+        ENV.rassoc("FOO".taint)
+      end.call
+    end
+  end
+
+  def test_taint_key
+    assert_raise(SecurityError) do
+      proc do
+        $SAFE = 2
+        ENV.key("FOO".taint)
+      end.call
+    end
+  end
+
+  def test_taint_key_p
+    assert_raise(SecurityError) do
+      proc do
+        $SAFE = 2
+        ENV.key?("FOO".taint)
+      end.call
+    end
+  end
+
+  def test_taint_value_p
+    assert_raise(SecurityError) do
+      proc do
+        $SAFE = 2
+        ENV.value?("FOO".taint)
+      end.call
+    end
+  end
+
+  def test_taint_aset_value
+    assert_raise(SecurityError) do
+      proc do
+        $SAFE = 2
+        ENV["FOO"] = "BAR".taint
+      end.call
+    end
+  end
+
+  def test_taint_aset_key
+    assert_raise(SecurityError) do
+      proc do
+        $SAFE = 2
+        ENV["FOO".taint] = "BAR"
+      end.call
+    end
+  end
 end
diff --git a/version.h b/version.h
index 7f06df1d59..49d79e07a1 100644
--- a/version.h
+++ b/version.h
@@ -1,10 +1,10 @@
 #define RUBY_VERSION "2.0.0"
-#define RUBY_RELEASE_DATE "2014-09-06"
-#define RUBY_PATCHLEVEL 556
+#define RUBY_RELEASE_DATE "2014-09-10"
+#define RUBY_PATCHLEVEL 557
 
 #define RUBY_RELEASE_YEAR 2014
 #define RUBY_RELEASE_MONTH 9
-#define RUBY_RELEASE_DAY 6
+#define RUBY_RELEASE_DAY 10
 
 #include "ruby/version.h"