Cisco IOS 12.0(5)XU through 12.1(2) allows remote attackers to read system administration and topology information via an "snmp-server host" command, which creates a readable "community" community string if one has not been previously created.
https://exchange.xforce.ibmcloud.com/vulnerabilities/6178
http://www.kb.cert.org/vuls/id/848944
http://www.cisco.com/warp/public/707/ios-snmp-community-vulns-pub.shtml