Here at Mandiant we deal with our fair share of malicious code.
Being able to quickly identify specific information about a piece of
malware is imperative. More specifically, knowing which domains a
piece of malware uses for command and control (C2) communication is
important to on-site incident responders.
To aid analysts in
DNS identification, I have written href="/content/fireeye-www/en_US/services/freeware/apatedns.html">ApateDNS.
It is a simple tool that acts as a phony DNS server that can log or
manipulate DNS requests being made to it. Malware analysts typically
use this to redirect beacon traffic from a guest virtual machine to
the host system (or another virtual machine) to monitor beacon
and/or communication channels using Netcat or a custom written C2
script. Forensic analysts typically use this tool to quickly extract
DNS names from malware samples.
ApateDNS automatically sets
up your Windows network configurations by attempting to determine
the default route or current DNS settings. This is most useful when
in a guest virtual machine since the default route is typically the
host machine. As shown in the figure below, ApateDNS has found the
default route in my virtual machine (192.168.239.1) and uses this IP
address for any DNS request on my virtual host. The user may
override this by specifying an IP address for DNS Reply IP.
Malware often uses multiple C2 domains. To catch this, ApateDNS
allows a user to specify a number of non-existent DNS (NXDOMAIN)
replies for any possible DNS lookup. As seen in the figure below,
the malware returns a single, non-existent domain for each DNS
request (since a "1" is entered for "# of
NXDOMAIN's"). The example malware beacons and detects if a
valid IP address has been resolved from a DNS request, if not, it
will continue to walk down its C2 domain list. By using the NXDOMAIN
functionality, we see three different DNS requests made by the
malware: evil1.example.com, evil2.example.com and
evil3.example.com.
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ApateDNS
gives malware analysts an easy way to control DNS on their machine
and forensic analysts a way to monitor DNS requests made by malware.
Of course, not all malware utilizes DNS and some may not beacon
without a specific set of conditions being satisfied. ApateDNS's use
cases are not limited just to malware. It can be used for any
purpose where a user may want to monitor outbound DNS requests or
traffic.
Feel free to check out ApateDNS href="/content/fireeye-www/en_US/services/freeware/apatedns.html">here.