supported groups extension with invalid length

prober.py

@@ -194,7 +194,10 @@
     SupportedGroupsNull12PFS(),
     SupportedGroupsOddLen(),
     SupportedGroupsOddLen12(),
-    SupportedGroupsOddLen12PFS()
+    SupportedGroupsOddLen12PFS(),
+    SupportedGroupsOverflow(),
+    SupportedGroupsOverflow12(),
+    SupportedGroupsOverflow12PFS()
 ]
 
 def probe(ipaddress, port, starttls, specified_probe):

probes.py

@@ -1798,3 +1798,24 @@ class SupportedGroupsOddLen12(SupportedGroupsOddLen, NormalHandshake12):
 class SupportedGroupsOddLen12PFS(SupportedGroupsOddLen, NormalHandshake12PFS):
     '''As with SupportedGroupsOddLen but in PFS TLSv1.2 hello'''
     pass
+
+
+class SupportedGroupsOverflow(SupportedGroupsNull):
+    '''Send supported groups extension with length larger than data'''
+
+    def test(self, sock):
+        logging.debug('Sending Client Hello...')
+        # normal extension has a two byte length and two byte elements,
+        # truncate the whole second element
+        sock.write(self.make_supported_groups_hello(b'\x00\x04\x00\x17'))
+
+
+class SupportedGroupsOverflow12(SupportedGroupsOverflow, NormalHandshake12):
+    '''As with SupportedGroupsOverflow but in TLSv1.2 hello'''
+    pass
+
+
+class SupportedGroupsOverflow12PFS(SupportedGroupsOverflow,
+        NormalHandshake12PFS):
+    '''As with SupportedGroupsOverflow but in PFS TLSv1.2 hello'''
+    pass

tests/test_probes.py

@@ -3643,3 +3643,68 @@ def test_test(self):
                           b'\x00\x09'
                           b'\x00\x0a\x00\x05'
                           b'\x00\x03\x00\x17\x00'])
+
+
+class TestSupportedGroupsOverflow(unittest.TestCase):
+    def test_test(self):
+        probe = SupportedGroupsOverflow()
+        sock = MockSock()
+
+        probe.test(sock)
+
+        self.maxDiff = None
+        self.assertEqual(sock.sent_data,
+                         [b'\x16\x03\x01\x00C'
+                          b'\x01\x00\x00?'
+                          b'\x03\x01' +
+                          RANDOM_STR +
+                          b'\x00'
+                          b'\x00\x0e' +
+                          DEFAULT_CIPHERS_STR +
+                          b'\x01\x00'
+                          b'\x00\x08'
+                          b'\x00\x0a\x00\x04'
+                          b'\x00\x04\x00\x17'])
+
+
+class TestSupportedGroupsOverflow12(unittest.TestCase):
+    def test_test(self):
+        probe = SupportedGroupsOverflow12()
+        sock = MockSock()
+
+        probe.test(sock)
+
+        self.assertEqual(sock.sent_data,
+                         [b'\x16\x03\x01\x00['
+                          b'\x01\x00\x00W'
+                          b'\x03\x03' +
+                          RANDOM_STR +
+                          b'\x00'
+                          b'\x00&' +
+                          DEFAULT_12_CIPHERS_STR +
+                          b'\x01\x00'
+                          b'\x00\x08'
+                          b'\x00\x0a\x00\x04'
+                          b'\x00\x04\x00\x17'])
+
+
+class TestSupportedGroupsOverflow12PFS(unittest.TestCase):
+    def test_test(self):
+        probe = SupportedGroupsOverflow12PFS()
+        sock = MockSock()
+
+        probe.test(sock)
+
+        self.maxDiff = None
+        self.assertEqual(sock.sent_data,
+                         [b"\x16\x03\x01\x00\x93"
+                          b"\x01\x00\x00\x8f"
+                          b"\x03\x03" +
+                          RANDOM_STR +
+                          b"\x00"
+                          b"\x00^" +
+                          DEFAULT_PFS_CIPHERS_STR +
+                          b"\x01\x00"
+                          b'\x00\x08'
+                          b'\x00\x0a\x00\x04'
+                          b'\x00\x04\x00\x17'])