53-DNS

The Domain Name System (DNS) is essential for the Internet. It translates domain names, like example.com, into IP addresses used by web servers. DNS resolves computer names to IP addresses and does not have a central database.

Default Port: 53

Different DNS servers

Server Type	Description
DNS Root Server	Handles top-level domains (TLDs) and links domain names to IP addresses. There are 13 root servers worldwide, managed by ICANN.
Authoritative Nameserver	Manages a specific zone and provides definitive answers for its area. If it can’t answer, the root server steps in.
Non-authoritative Nameserver	Gathers DNS information from other servers but isn’t responsible for a specific zone.
Caching DNS Server	Stores information from other servers temporarily based on the authoritative server’s settings.
Forwarding Server	Forwards DNS queries to another server.
Resolver	Resolves domain names locally on a computer or router, not an authoritative server.

DNS records

DNS Record	Description
A	Provides the IPv4 address for the domain.
AAAA	Provides the IPv6 address for the domain.
MX	Lists the mail servers for the domain.
NS	Lists the DNS servers (nameservers) for the domain.
TXT	Contains various information, such as validation for Google Search Console, SSL certificates, and SPF/DMARC records for email security.
CNAME	Acts as an alias for another domain. For example, www.example.com can point to the same IP as example.com.
PTR	Performs reverse lookups by converting IP addresses to domain names.
SOA	Provides details about the DNS zone and the administrative contact’s email address.

WHOIS

WHOIS is a client for the whois directory service.

whois example.com

Each WHOIS record typically contains the following information:

Field	Description
Domain Name	The registered domain. (e.g., example.com)
Registrar	The company where the domain was registered. (e.g., GoDaddy, Namecheap)
Registrant Contact	The person or organization that owns the domain.
Administrative Contact	The person responsible for managing the domain.
Technical Contact	The person handling technical issues for the domain.
Creation Date	When the domain was registered.
Expiration Date	When the domain is set to expire.
Name Servers	Servers that translate the domain name into an IP address.

Dig

Dig (domain information groper) is a flexible tool for interrogating DNS name servers. It performs DNS lookups and displays the answers that are returned from the name server(s) that were queried.

# DNS zone / email
dig soa example.com
 
# Nameserver
dig ns example.com
 
# DNS server version
dig CH TXT version.bind $IP
 
# All the records
dig any example.com @$IP
 
# Zone transfer
dig axfr example.com @$IP
 
# Bash oneliner subdomain bruteforce
for sub in $(cat /wordlists/subdomains.txt);do dig $sub.example.com @$IP | grep -v ';\|SOA' | sed -r '/^\s*$/d' | grep $sub | tee -a subdomains.txt;done

DNSrecon

Dnsrecon is a python script for DNS enumeration.

# Enumerate general DNS records for a given domain such as MX,SOA,NS,A, etc
dnsrecon -d example.com

DNSenum

Dnsenum is a perl script that enumerates DNS information.

# Subdomain bruteforce
dnsenum --dnsserver $IP --enum -p 0 -s 0 -o subdomains.txt -f /wordlists/subdomains.txt example.com

ZoneTransfer

Description

The zone transfer is how a secondary DNS server receives information from the primary DNS server and updates it. There’s web based tool that can performing the zone transfer automatically or doing it manually using nslookup.

# Identifying nameservers
nslookup -type=NS example.com
 
# Performing the zone transfer
nslookup -type=any -query=AXFR example.com ns.example.com

Config files

named.conf.local     # contains local DNS zone config and custom settings
named.conf.options   # includes global options and server-wide settings
named.conf.log       # logging options for BIND to manage and record DNS activity

Dangerous settings

DNS servers can be attacked in various ways. For example, a list of vulnerabilities targeting the BIND9 server can be found at CVEdetails, and SecurityTrails highlights common DNS server attacks.

Certain settings mentioned below can contribute to these vulnerabilities.

Option	Description
allow-query	Specifies which hosts can send requests to the DNS server.
allow-recursion	Specifies which hosts can make recursive requests to the DNS server.
allow-transfer	Specifies which hosts can receive zone transfers from the DNS server.
zone-statistic	Collects statistics about DNS zones.