Cisco SNMP ACL Bypass Script

Author: Martin Voelk
February 2, 2016

We all know that Cisco is one of the key players in the Routing & Switching market. Often Perimeter Routers are made up of Cisco models of all kind. We also know that SNMP is one of the most popular Network Management protocols.

In many Penetration Tests we come across scenarios where customers try to protect SNMP polling with Access Lists. This is a good way of thinking but then leaving RO communities to “public” and RW communities to “private” is not a good idea. IP spoofing and bypassing ACLs is a very very simple task to perform.

We still see that the majority of clients (especially in the Small and Medium sized arena) still use SNMPv2 instead of the much more secure authenticated and encrypted v3. We also see that Anti Spoofing features like Unicast RPF are rarely configured outside Enterprise networks (and even there they are often not).

A very smart tool has been developed and put on Github which enables ACL bypass. We advice to check your Cisco perimeter routers and test it out with that little neat tool. And please change your community strings to something better 🙂