# 53 - Pentesting DNS ## **Basic Information** The Domain Name Systems \(DNS\) is the phonebook of the Internet. Humans access information online through domain names, like nytimes.com or espn.com. Web browsers interact through Internet Protocol \(IP\) addresses. DN S translates domain names to [IP addresses](https://www.cloudflare.com/learning/dns/glossary/what-is-my-ip-address/) so browsers can load Internet resources. From [here](https://www.cloudflare.com/learning/dns/what-is-dns/). **Default port:** 53 ```text PORT STATE SERVICE REASON 53/tcp open domain Microsoft DNS 6.1.7601 (1DB15D39) (Windows Server 2008 R2 SP1) 5353/udp open zeroconf udp-response 53/udp open domain Microsoft DNS 6.1.7601 (1DB15D39) (Windows Server 2008 R2 SP1) ``` ## Enumeration ### **Banner Grabbing** DNS does not have a "banner" to grab. The closest equivalent is a magic query for `version.bind. CHAOS TXT` which will work on most BIND nameservers. You can perform this query using `dig`: ```bash dig version.bind CHAOS TXT @DNS ``` If that does not work you can use fingerprinting techniques to determine the remote server's version -- the [`fpdns`](https://github.com/kirei/fpdns) tool is one option for that, but there are others. You can grab the banner also with a **nmap** script: ```text --script dns-nsid ``` ### **Zone Transfer** ```bash dig axfr @ #Try zone transfer without domain dig axfr @ #Try zone transfer guessing the domain fierce -dns #Will try toperform a zone transfer against every authoritative name server and if this doesn'twork, will launch a dictionary attack ``` ### More info ```bash dig ANY @ #Any information dig A @ #Regular DNS request dig AAAA @ #IPv6 DNS request dig TXT @ #Information dig MX @ #Emails related dig NS @ #DNS that resolves that name dig -x 192.168.0.2 @ #Reverse lookup dig -x 2a00:1450:400c:c06::93 @ #reverse IPv6 lookup #Use [-p PORT] or -6 (to use ivp6 address of dns) ``` #### Using nslookup ```bash nslookup > SERVER #Select dns server > 127.0.0.1 #Reverse lookup of 127.0.0.1, maybe... > #Reverse lookup of a machine, maybe... ``` ### Useful metasploit modules ```bash auxiliary/gather/enum_dns #Perform enumeration actions ``` ### Useful nmap scripts ```bash #Perform enumeration actions nmap -n --script "(default and *dns*) or fcrdns or dns-srv-enum or dns-random-txid or dns-random-srcport" ``` ### DNS - Reverse BF ```bash dnsrecon -r 127.0.0.0/24 -n #DNS reverse of all of the addresses dnsrecon -r 127.0.1.0/24 -n #DNS reverse of all of the addresses dnsrecon -r /24 -n #DNS reverse of all of the addresses dnsrecon -d active.htb -a -n #Zone transfer ``` {% hint style="info" %} If you are able to find subdomains resolving to internal IP-addresses, you should try to perform a reverse dns BF to the NSs of the domain asking for that IP range. {% endhint %} Another tool to do so: [https://github.com/amine7536/reverse-scan](https://github.com/amine7536/reverse-scan) You can query reverse IP ranges to [https://bgp.he.net/net/205.166.76.0/24\#\_dns](https://bgp.he.net/net/205.166.76.0/24#_dns) \(this tool is also helpful with BGP\). ### DNS - Subdomains BF ```bash dnsrecon -D subdomains-1000.txt -d -n dnscan -d -r -w subdomains-1000.txt #Bruteforce subdomains in recursive way, https://github.com/rbsec/dnscan ``` ### Active Directory servers ```text dig -t _gc._tcp.lab.domain.com dig -t _ldap._tcp.lab.domain.com dig -t _kerberos._tcp.lab.domain.com dig -t _kpasswd._tcp.lab.domain.com nmap --script dns-srv-enum --script-args "dns-srv-enum.domain='domain.com'" ``` ### DNSSec ```bash #Query paypal subdomains to ns3.isc-sns.info nmap -sSU -p53 --script dns-nsec-enum --script-args dns-nsec-enum.domains=paypal.com ns3.isc-sns.info ``` ### IPv6 Brute force using "AAAA" requests to gather IPv6 of the subdomains. ```bash dnsdict6 -s -t ``` Bruteforce reverse DNS in using IPv6 addresses ```bash dnsrevenum6 pri.authdns.ripe.net 2001:67c:2e8::/48 #Will use the dns pri.authdns.ripe.net ``` ### DNS Recursion DDoS If **DNS recursion is enabled**, an attacker could **spoof** the **origin** on the UDP packet in order to make the **DNS send the response to the victim server**. An attacker could abuse **ANY** or **DNSSEC** record types as they use to have the bigger responses. The way to **check** if a DNS supports **recursion** is to query a domain name and **check** if the **flag "ra"** \(_recursion available_\) is in the response: ```bash dig google.com A @ ``` **Non available**: ![](../.gitbook/assets/image%20%28155%29.png) **Available**: ![](../.gitbook/assets/image%20%28139%29.png) ### Mail to nonexistent account From book: Network Security Assessment \(3rd edition\) Simply sending an email message to a nonexistent address at a target domain often reveals useful internal network information through a _nondelivery notification_ \(NDN\). ```text Generating server: noa.nintendo.com blah@nintendo.com #550 5.1.1 RESOLVER.ADR.RecipNotFound; not found ## Original message headers: Received: from ONERDEDGE02.one.nintendo.com (10.13.20.35) by onerdexch08.one.nintendo.com (10.13.30.39) with Microsoft SMTP Server (TLS) id 14.3.174.1; Sat, 26 Apr 2014 16:52:22 -0700 Received: from barracuda.noa.nintendo.com (205.166.76.35) by ONERDEDGE02.one.nintendo.com (10.13.20.35) with Microsoft SMTP Server (TLS) id 14.3.174.1; Sat, 26 Apr 2014 16:51:22 -0700 X-ASG-Debug-ID: 1398556333-0614671716199b0d0001-zOQ9WJ Received: from gateway05.websitewelcome.com (gateway05.websitewelcome.com [69.93.154.37]) by barracuda.noa.nintendo.com with ESMTP id xVNPkwaqGgdyH5Ag for ; Sat, 26 Apr 2014 16:52:13 -0700 (PDT) X-Barracuda-Envelope-From: chris@example.org X-Barracuda-Apparent-Source-IP: 69.93.154.37 ``` The following data in this transcript is useful: * Internal hostnames, IP addresses, and subdomain layout * The mail server is running Microsoft Exchange Server 2010 SP3 * A Barracuda Networks device is used to perform content filtering ## Config files ```text host.conf resolv.conf named.conf ```