LoFP LoFP / exclude dns servers from this rule as this is expected behavior. endpoints usually query local dns servers defined in their dhcp scopes, but this may be overridden if a user configures their endpoint to use a remote dns server. this is uncommon in managed enterprise networks because it could break intranet name resolution when split horizon dns is utilized. some consumer vpn services and browser plug-ins may send dns traffic to remote internet destinations. in that case, such devices or networks can be excluded from this rule when this is expected behavior.

Techniques

Sample rules

DNS Activity to the Internet

Description

This rule detects when an internal network client sends DNS traffic directly to the Internet. This is atypical behavior for a managed network and can be indicative of malware, exfiltration, command and control, or simply misconfiguration. This DNS activity also impacts your organization’s ability to provide enterprise monitoring and logging of DNS, and it opens your network to a variety of abuses and malicious communications.

Detection logic

event.category:(network or network_traffic) and (event.type:connection or type:dns) and (destination.port:53 or event.dataset:zeek.dns)
  and source.ip:(
    10.0.0.0/8 or
    172.16.0.0/12 or
    192.168.0.0/16
  ) and
  not destination.ip:(
    10.0.0.0/8 or
    127.0.0.0/8 or
    169.254.0.0/16 or
    172.16.0.0/12 or
    192.0.0.0/24 or
    192.0.0.0/29 or
    192.0.0.8/32 or
    192.0.0.9/32 or
    192.0.0.10/32 or
    192.0.0.170/32 or
    192.0.0.171/32 or
    192.0.2.0/24 or
    192.31.196.0/24 or
    192.52.193.0/24 or
    192.168.0.0/16 or
    192.88.99.0/24 or
    224.0.0.0/4 or
    100.64.0.0/10 or
    192.175.48.0/24 or
    198.18.0.0/15 or
    198.51.100.0/24 or
    203.0.113.0/24 or
    240.0.0.0/4 or
    "::1" or
    "FE80::/10" or
    "FF00::/8"
  )