Rule:

--
Sid:
1893

--
Summary:
This event is generated when SNMP communications do not contain a 
community name.

--
Impact:
Medium to Serious. Depending on if the community string was for 
read-only, read-create or read-write an attacker could gain a varying 
level of access to a system.

--
Detailed Information:
An SNMP community string is the authentication process that a host 
running SNMP uses to grant access. By supplying a blank community string
and attacker may be attempting to gain access to SNMP functionality for
a device that has not been configured correctly.

--
Affected Systems:
Numerous. Routers, switches, servers, NAS systems, many others.

--
Attack Scenarios:
An attacker can launch a scan of all network attached devices looking 
for port 161 (UDP) and then attempt to gain access using SNMP.

--
Ease of Attack:
Simple. There are many free SNMP "tree walking" programs, an example of 
such is getIF.

--
False Positives:
None Known

--
False Negatives:
None Known

--
Corrective Action:
Ensure that all devices using SNMP have a community string assigned.

Make sure that all devices that have SNMP turned on have complex 
passwords assigned.

Disable unneeded WRITE / CREATE community strings.

Since SNMP traffic is not encrypted, use a packet filtering firewall to 
restrict SNMP communications to the protected network.

--
Contributors:
Sourcefire Research Team
Brian Caswell <bmc@sourcefire.com>
Nigel Houghton <nigel.houghton@sourcefire.com>
Snort documentation contributed by  Mike Rivett ebiz@rivett.org

-- 
Additional References:

GetIF:
http://www.wtcs.org/snmp4tpc/getif.htm

CVE:
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-1999-0517

--
