diff --git a/Doc/howto/urllib2.rst b/Doc/howto/urllib2.rst
index 6bb06d4..9fb577d 100644
--- a/Doc/howto/urllib2.rst
+++ b/Doc/howto/urllib2.rst
@@ -525,6 +525,15 @@ setting up a `Basic Authentication`_ handler: ::
     through a proxy.  However, this can be enabled by extending urllib2 as
     shown in the recipe [#]_.
 
+.. note::
+
+    If the environment variable ``REQUEST_METHOD`` is set, which usually
+    indicates your script is running in a CGI environment, the environment
+    variable ``HTTP_PROXY`` will be ignored. This is because that variable can
+    be injected by a client using the "Proxy:" HTTP header. If you need to use
+    an HTTP proxy in a CGI environment, either use ``ProxyHandler`` explicitly,
+    or make sure the variable name is in lowercase (``http_proxy``).
+
 
 Sockets and Layers
 ==================
diff --git a/Doc/library/urllib.rst b/Doc/library/urllib.rst
index 3b5dc16..38aa2ff 100644
--- a/Doc/library/urllib.rst
+++ b/Doc/library/urllib.rst
@@ -295,6 +295,14 @@ Utility functions
    If both lowercase and uppercase environment variables exist (and disagree),
    lowercase is preferred.
 
+   Note that if the environment variable ``REQUEST_METHOD`` is set, which
+   usually indicates your script is running in a CGI environment, the
+   environment variable ``HTTP_PROXY`` (uppercase) will be ignored. This is
+   because that variable can be injected by a client using the "Proxy:" HTTP
+   header. If you need to use an HTTP proxy in a CGI environment, either use
+   ``ProxyHandler`` explicitly, or make sure the variable name is in lowercase
+   (``http_proxy``)
+
 .. note::
     urllib also exposes certain utility functions like splittype, splithost and
     others parsing URL into various components. But it is recommended to use
diff --git a/Doc/library/urllib2.rst b/Doc/library/urllib2.rst
index 8a4c80e..5262aea 100644
--- a/Doc/library/urllib2.rst
+++ b/Doc/library/urllib2.rst
@@ -229,6 +229,14 @@ The following classes are provided:
 
    To disable autodetected proxy pass an empty dictionary.
 
+    Note that if the environment variable ``REQUEST_METHOD`` is set, which
+    usually indicates your script is running in a CGI environment, the
+    environment variable ``HTTP_PROXY`` (uppercase) will be ignored. This is
+    because that variable can be injected by a client using the "Proxy:" HTTP
+    header. If you need to use an HTTP proxy in a CGI environment, either use
+    ``ProxyHandler`` explicitly, or make sure the variable name is in lowercase
+    (``http_proxy``).
+
 
 .. class:: HTTPPasswordMgr()
 
diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index 434d533..27a1d38 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -170,6 +170,18 @@ class ProxyTests(unittest.TestCase):
         self.assertTrue(urllib.proxy_bypass_environment('anotherdomain.com:8888'))
         self.assertTrue(urllib.proxy_bypass_environment('newdomain.com:1234'))
 
+    def test_proxy_cgi_ignore(self):
+        try:
+            self.env.set('HTTP_PROXY', 'http://somewhere:3128')
+            proxies = urllib.getproxies_environment()
+            self.assertEqual('http://somewhere:3128', proxies['http'])
+            self.env.set('REQUEST_METHOD', 'GET')
+            proxies = urllib.getproxies_environment()
+            self.assertNotIn('http', proxies)
+        finally:
+            self.env.unset('REQUEST_METHOD')
+            self.env.unset('HTTP_PROXY')
+
     def test_proxy_bypass_environment_host_match(self):
         bypass = urllib.proxy_bypass_environment
         self.env.set('NO_PROXY',
diff --git a/Lib/urllib.py b/Lib/urllib.py
index 139fab9..b159523 100644
--- a/Lib/urllib.py
+++ b/Lib/urllib.py
@@ -1380,12 +1380,20 @@ def getproxies_environment():
     If you need a different way, you can pass a proxies dictionary to the
     [Fancy]URLopener constructor.
     """
+    # Get all variables
     proxies = {}
     for name, value in os.environ.items():
         name = name.lower()
         if value and name[-6:] == '_proxy':
             proxies[name[:-6]] = value
 
+    # If we are running as CGI script, forget HTTP_PROXY (uppercase) as it
+    # may be set from the web server by a "Proxy:" header from the client
+    # If lowercase, it will still be used thanks to the next block
+    if 'REQUEST_METHOD' in os.environ:
+        proxies.pop('http', None)
+
+    # Get lowercase variables
     for name, value in os.environ.items():
         if name[-6:] == '_proxy':
             name = name.lower()