CVE-2021-28363

@@ -490,6 +490,10 @@ def _connect_tls_proxy(self, hostname, conn):
             self.ca_cert_dir,
             self.ca_cert_data,
         )
+        # By default urllib3's SSLContext disables `check_hostname` and uses
+        # a custom check. For proxies we're good with relying on the default
+        # verification.
+        ssl_context.check_hostname = True
 
         # If no cert was provided, use only the default options for server
         # certificate validation

@@ -64,6 +64,17 @@ def no_san_server(tmp_path_factory):
         yield cfg
 
 
+@pytest.fixture
+def no_localhost_san_server(tmp_path_factory):
+    tmpdir = tmp_path_factory.mktemp("certs")
+    ca = trustme.CA()
+    # non localhost common name
+    server_cert = ca.issue_cert(u"example.com")
+
+    with run_server_in_thread("https", "localhost", tmpdir, ca, server_cert) as cfg:
+        yield cfg
+
+
 @pytest.fixture
 def ip_san_server(tmp_path_factory):
     tmpdir = tmp_path_factory.mktemp("certs")

@@ -543,3 +543,25 @@ def test_basic_ipv6_proxy(self):
 
             r = http.request("GET", "%s/" % self.https_url)
             assert r.status == 200
+
+
+class TestHTTPSProxyVerification:
+    @onlyPy3
+    def test_https_proxy_hostname_verification(self, no_localhost_san_server):
+        bad_server = no_localhost_san_server
+        bad_proxy_url = "https://%s:%s" % (bad_server.host, bad_server.port)
+
+        # An exception will be raised before we contact the destination domain.
+        test_url = "testing.com"
+        with proxy_from_url(bad_proxy_url, ca_certs=bad_server.ca_certs) as https:
+            with pytest.raises(MaxRetryError) as e:
+                https.request("GET", "http://%s/" % test_url)
+            assert isinstance(e.value.reason, SSLError)
+            assert "hostname 'localhost' doesn't match" in str(e.value.reason)
+
+            with pytest.raises(MaxRetryError) as e:
+                https.request("GET", "https://%s/" % test_url)
+            assert isinstance(e.value.reason, SSLError)
+            assert "hostname 'localhost' doesn't match" in str(
+                e.value.reason
+            ) or "Hostname mismatch" in str(e.value.reason)