# 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 @<DNS_IP> #Try zone transfer without domain
dig axfr @<DNS_IP> <DOMAIN> #Try zone transfer guessing the domain
fierce --domain <DOMAIN> --dns-servers <DNS_IP> #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 @<DNS_IP> <DOMAIN>     #Any information
dig A @<DNS_IP> <DOMAIN>       #Regular DNS request
dig AAAA @<DNS_IP> <DOMAIN>    #IPv6 DNS request
dig TXT @<DNS_IP> <DOMAIN>     #Information
dig MX @<DNS_IP> <DOMAIN>      #Emails related
dig NS @<DNS_IP> <DOMAIN>      #DNS that resolves that name
dig -x 192.168.0.2 @<DNS_IP>   #Reverse lookup
dig -x 2a00:1450:400c:c06::93 @<DNS_IP> #reverse IPv6 lookup

#Use [-p PORT]  or  -6 (to use ivp6 address of dns)
```

#### Using nslookup

```bash
nslookup
> SERVER <IP_DNS> #Select dns server
> 127.0.0.1 #Reverse lookup of 127.0.0.1, maybe...
> <IP_MACHINE> #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" <IP>
```

### DNS - Reverse BF

```bash
dnsrecon -r 127.0.0.0/24 -n <IP_DNS>  #DNS reverse of all of the addresses
dnsrecon -r 127.0.1.0/24 -n <IP_DNS>  #DNS reverse of all of the addresses
dnsrecon -r <IP_DNS>/24 -n <IP_DNS>   #DNS reverse of all of the addresses
dnsrecon -d active.htb -a -n <IP_DNS> #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 <DOMAIN> -n <IP_DNS>
dnscan -d <domain> -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 <domain>
```

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 @<IP>
```

**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 <blah@nintendo.com>; 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
```

## HackTricks Automatic Commands

```text
Protocol_Name: DNS    #Protocol Abbreviation if there is one.
Port_Number:  53     #Comma separated if there is more than one.
Protocol_Description: Domain Name Service        #Protocol Abbreviation Spelled out

Name: Notes
Description: Notes for DNS
Note: """
#These are the commands I run every time I see an open DNS port

dnsrecon -r 127.0.0.0/24 -n {IP} -d {Domain_Name}
dnsrecon -r 127.0.1.0/24 -n {IP} -d {Domain_Name}
dnsrecon -r {Network}{CIDR} -n {IP} -d {Domain_Name}
dig axfr @{IP}
dig axfr {Domain_Name} @{IP}
nslookup
    SERVER {IP}
    127.0.0.1
    {IP}
    Domain_Name
    exit

https://book.hacktricks.xyz/pentesting/pentesting-dns
"""

Name: Banner Grab
Description: Grab DNS Banner
Command: """dig version.bind CHAOS TXT @DNS"""

Name: Nmap Vuln Scan
Description: Scan for Vulnerabilities with Nmap
Command: """nmap -n --script "(default and *dns*) or fcrdns or dns-srv-enum or dns-random-txid or dns-random-srcport" {IP}"""

Name: Zone Transfer
Description: Three attempts at forcing a zone transfer
Command: dig axfr @{IP} && dix axfr @{IP} {Domain_Name} && fierce -dns {Domain_Name}

Name: Active Directory
Description: Eunuerate a DC via DNS
Command: dig -t _gc._{Domain_Name} && dig -t _ldap._{Domain_Name} && dig -t _kerberos._{Domain_Name} && dig -t _kpasswd._{Domain_Name} && nmap --script dns-srv-enum --script-args "dns-srv-enum.domain={Domain_Name}"
```

