[merge from 3.4] - Prevent HTTPoxy attack (CVE-2016-1000110)

Ignore the HTTP_PROXY variable when REQUEST_METHOD environment is set, which
indicates that the script is in CGI mode.

Issue #27568 Reported and patch contributed by Rémi Rampin.

5 files changed, 42 insertions, 0 deletions

diff --git a/Doc/howto/urllib2.rst b/Doc/howto/urllib2.rst
index 24a4156..d2c7991 100644
--- a/Doc/howto/urllib2.rst
+++ b/Doc/howto/urllib2.rst
@@ -538,6 +538,11 @@ setting up a `Basic Authentication`_ handler: ::
     through a proxy.  However, this can be enabled by extending urllib.request as
     shown in the recipe [#]_.
 
+.. note::
+
+    ``HTTP_PROXY`` will be ignored if a variable ``REQUEST_METHOD`` is set; see
+    the documentation on :func:`~urllib.request.getproxies`.
+
 
 Sockets and Layers
 ==================
diff --git a/Doc/library/urllib.request.rst b/Doc/library/urllib.request.rst
index 6c1bfb8..1291aeb 100644
--- a/Doc/library/urllib.request.rst
+++ b/Doc/library/urllib.request.rst
@@ -173,6 +173,16 @@ The :mod:`urllib.request` module defines the following functions:
    If both lowercase and uppercase environment variables exist (and disagree),
    lowercase is preferred.
 
+    .. 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`` (uppercase ``_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 (or at least the ``_proxy`` suffix).
+
 
 The following classes are provided:
 
@@ -280,6 +290,11 @@ The following classes are provided:
    list of hostname suffixes, optionally with ``:port`` appended, for example
    ``cern.ch,ncsa.uiuc.edu,some.host:8080``.
 
+    .. note::
+
+       ``HTTP_PROXY`` will be ignored if a variable ``REQUEST_METHOD`` is set;
+       see the documentation on :func:`~urllib.request.getproxies`.
+
 
 .. class:: HTTPPasswordMgr()
 
diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index 5d05f8d..c26c52a 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -232,6 +232,18 @@ class ProxyTests(unittest.TestCase):
         self.assertTrue(urllib.request.proxy_bypass_environment('anotherdomain.com:8888'))
         self.assertTrue(urllib.request.proxy_bypass_environment('newdomain.com:1234'))
 
+    def test_proxy_cgi_ignore(self):
+        try:
+            self.env.set('HTTP_PROXY', 'http://somewhere:3128')
+            proxies = urllib.request.getproxies_environment()
+            self.assertEqual('http://somewhere:3128', proxies['http'])
+            self.env.set('REQUEST_METHOD', 'GET')
+            proxies = urllib.request.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.request.proxy_bypass_environment
         self.env.set('NO_PROXY',
diff --git a/Lib/urllib/request.py b/Lib/urllib/request.py
index 1731fe3..3be327d 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -2412,6 +2412,12 @@ def getproxies_environment():
         name = name.lower()
         if value and name[-6:] == '_proxy':
             proxies[name[:-6]] = value
+    # CVE-2016-1000110 - If we are running as CGI script, forget HTTP_PROXY
+    # (non-all-lowercase) as it may be set from the web server by a "Proxy:"
+    # header from the client
+    # If "proxy" is lowercase, it will still be used thanks to the next block
+    if 'REQUEST_METHOD' in os.environ:
+        proxies.pop('http', None)
     for name, value in os.environ.items():
         if name[-6:] == '_proxy':
             name = name.lower()
diff --git a/Misc/NEWS b/Misc/NEWS
index 6b2b419..efe9b28 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -34,6 +34,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #27568: Prevent HTTPoxy attack (CVE-2016-1000110). Ignore the
+  HTTP_PROXY variable when REQUEST_METHOD environment is set, which indicates
+  that the script is in CGI mode.
+
 - Issue #27130: In the "zlib" module, fix handling of large buffers
   (typically 4 GiB) when compressing and decompressing.  Previously, inputs
   were limited to 4 GiB, and compression and decompression operations did not