[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.

2 files changed, 20 insertions, 0 deletions

diff --git a/Doc/howto/urllib2.rst b/Doc/howto/urllib2.rst
index 24a415604f..d2c799196b 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 6c1bfb8b1f..1291aebcd2 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()