diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 627275891fb3b2..5220891cbb2ac5 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -385,6 +385,46 @@ def test_env(self):
         self.addCleanup(p.stdout.close)
         self.assertEqual(p.stdout.read(), "orange")
 
+    def test_invalid_cmd(self):
+        # null character in the command name
+        cmd = sys.executable + '\0'
+        with self.assertRaises(TypeError):
+            subprocess.Popen([cmd, "-c", "pass"])
+
+        # null character in the command argument
+        with self.assertRaises(TypeError):
+            subprocess.Popen([sys.executable, "-c", "pass#\0"])
+
+    def test_invalid_env(self):
+        # null character in the enviroment variable name
+        newenv = os.environ.copy()
+        newenv["FRUIT\0VEGETABLE"] = "cabbage"
+        with self.assertRaises(TypeError):
+            subprocess.Popen([sys.executable, "-c", "pass"], env=newenv)
+
+        # null character in the enviroment variable value
+        newenv = os.environ.copy()
+        newenv["FRUIT"] = "orange\0VEGETABLE=cabbage"
+        with self.assertRaises(TypeError):
+            subprocess.Popen([sys.executable, "-c", "pass"], env=newenv)
+
+        # equal character in the enviroment variable name
+        newenv = os.environ.copy()
+        newenv["FRUIT=ORANGE"] = "lemon"
+        with self.assertRaises(ValueError):
+            subprocess.Popen([sys.executable, "-c", "pass"], env=newenv)
+
+        # equal character in the enviroment variable value
+        newenv = os.environ.copy()
+        newenv["FRUIT"] = "orange=lemon"
+        p = subprocess.Popen([sys.executable, "-c",
+                              'import sys, os;'
+                              'sys.stdout.write(os.getenv("FRUIT"))'],
+                             stdout=subprocess.PIPE,
+                             env=newenv)
+        stdout, stderr = p.communicate()
+        self.assertEqual(stdout, "orange=lemon")
+
     def test_communicate_stdin(self):
         p = subprocess.Popen([sys.executable, "-c",
                               'import sys;'
diff --git a/Misc/NEWS b/Misc/NEWS
index 30e3877718decc..564c8df9923fc3 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -52,6 +52,9 @@ Extension Modules
 Library
 -------
 
+- [Security] bpo-30730: Prevent environment variables injection in subprocess on
+  Windows.  Prevent passing other environment variables and command arguments.
+
 - [Security] bpo-30694: Upgrade expat copy from 2.2.0 to 2.2.1 to get fixes
   of multiple security vulnerabilities including: CVE-2017-9233 (External
   entity infinite loop DoS), CVE-2016-9063 (Integer overflow, re-fix),
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index ad505364bda9da..ffeb715c9f156e 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -3315,6 +3315,12 @@ posix_execve(PyObject *self, PyObject *args)
         {
             goto fail_2;
         }
+        /* Search from index 1 because on Windows starting '=' is allowed for
+           defining hidden environment variables. */
+        if (*k == '\0' || strchr(k + 1, '=') != NULL) {
+            PyErr_SetString(PyExc_ValueError, "illegal environment variable name");
+            goto fail_2;
+        }
 
 #if defined(PYOS_OS2)
         /* Omit Pseudo-Env Vars that Would Confuse Programs if Passed On */
diff --git a/PC/_subprocess.c b/PC/_subprocess.c
index ffe8f41d573df0..f73d14f57930f2 100644
--- a/PC/_subprocess.c
+++ b/PC/_subprocess.c
@@ -352,7 +352,7 @@ getenvironment(PyObject* environment)
     p = PyString_AS_STRING(out);
 
     for (i = 0; i < envsize; i++) {
-        int ksize, vsize, totalsize;
+        size_t ksize, vsize, totalsize;
         PyObject* key = PyList_GET_ITEM(keys, i);
         PyObject* value = PyList_GET_ITEM(values, i);
 
@@ -363,10 +363,22 @@ getenvironment(PyObject* environment)
         }
         ksize = PyString_GET_SIZE(key);
         vsize = PyString_GET_SIZE(value);
+        if (strlen(PyString_AS_STRING(key)) != ksize ||
+            strlen(PyString_AS_STRING(value)) != vsize)
+        {
+            PyErr_SetString(PyExc_TypeError, "embedded null character");
+            goto error;
+        }
+        /* Search from index 1 because on Windows starting '=' is allowed for
+           defining hidden environment variables. */
+        if (ksize == 0 || strchr(PyString_AS_STRING(key) + 1, '=') != NULL) {
+            PyErr_SetString(PyExc_ValueError, "illegal environment variable name");
+            goto error;
+        }
         totalsize = (p - PyString_AS_STRING(out)) + ksize + 1 +
                                                      vsize + 1 + 1;
         if (totalsize > PyString_GET_SIZE(out)) {
-            int offset = p - PyString_AS_STRING(out);
+            size_t offset = p - PyString_AS_STRING(out);
             if (_PyString_Resize(&out, totalsize + 1024))
                 goto exit;
             p = PyString_AS_STRING(out) + offset;