zeek/scripts/policy/protocols/dns/detect-external-names.zeek
2021-10-20 09:57:09 -07:00

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##! This script detects names which are not within zones considered to be
##! local but resolving to addresses considered local.
##! The :zeek:id:`Site::local_zones` variable **must** be set appropriately for
##! this detection.
@load base/frameworks/notice
@load base/utils/site
module DNS;
export {
redef enum Notice::Type += {
## Raised when a non-local name is found to be pointing at a
## local host. The :zeek:id:`Site::local_zones` variable
## **must** be set appropriately for this detection.
External_Name,
};
}
event dns_A_reply(c: connection, msg: dns_msg, ans: dns_answer, a: addr) &priority=-3
{
if ( |Site::local_zones| == 0 )
return;
# Check for responses from remote hosts that point at local hosts
# but the name is not considered to be within a "local" zone.
if ( Site::is_local_addr(a) && # referring to a local host
! Site::is_local_name(ans$query) ) # name isn't in a local zone.
{
NOTICE([$note=External_Name,
$msg=fmt("%s is pointing to a local host - %s.", ans$query, a),
$conn=c,
$identifier=cat(a,ans$query)]);
}
}