Implement a basic SNMP listener

All community strings are logged as they are sent to the server.
This initial implementation only supports SNMPv1 and SNMPv2c.

`pyasn1` is required for this server to function.

servers/SNMP.py

@@ -0,0 +1,50 @@
+#!/usr/bin/env python
+# This file is part of Responder, a network take-over set of tools
+# created and maintained by Laurent Gaffie.
+# email: laurent.gaffie@gmail.com
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+from utils import *
+
+if settings.Config.PY2OR3 == "PY3":
+    from socketserver import BaseRequestHandler
+else:
+    from SocketServer import BaseRequestHandler
+
+from pyasn1.codec.der.decoder import decode
+
+
+class SNMP(BaseRequestHandler):
+    def handle(self):
+        data = self.request[0]
+        received_record, rest_of_substrate = decode(data)
+
+        snmp_version = int(received_record['field-0'])
+
+        if snmp_version > 1:
+            # TODO: Add support for SNMPv3 (which will have a field-0 value of 2)
+            print(text("[SNMP] Unsupported SNMPv3 request received from %s" % self.client_address[0].replace("::ffff:","")))
+            return
+
+        community_string = str(received_record['field-1'])
+
+        SaveToDb(
+            {
+                "module": "SNMP",
+                "type": "Cleartext",
+                "client": self.client_address[0],
+                "user": community_string,
+                "cleartext": community_string,
+                "fullhash": community_string,
+            }
+        )