ICMP information such as (1) netmask and (2) timestamp is allowed from arbitrary hosts.
https://exchange.xforce.ibmcloud.com/vulnerabilities/322
https://exchange.xforce.ibmcloud.com/vulnerabilities/306
http://kb.vmware.com/selfservice/microsites/search.do?cmd=displayKC&externalId=1434
http://kb.juniper.net/InfoCenter/index?page=content&id=JSA10705