[merge from 3.5] - 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, 18 insertions, 0 deletions

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 67e73f9..dc436bc 100644
--- a/Lib/urllib/request.py
+++ b/Lib/urllib/request.py
@@ -2477,6 +2477,12 @@ 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()