Out-of-Band DNS Bind Server Setup (Manual Guide)

Note: Be sure to replace all instances of example.com with your actual domain and <Your Server IP> with your server IP address during configuration.

Overview

Out-Of-Band (OOB) techniques offer attackers a strategic approach to confirm and exploit vulnerabilities that might be otherwise classified as "blind." In scenarios where direct responses to requests are not available, OOB methods leverage the capability of vulnerable systems to generate outbound traffic, such as TCP, UDP, or ICMP requests. This allows an attacker to exfiltrate data discreetly, utilizing the inherent behavior of the target to bypass conventional security measures.

In the context of DNS, setting up an OOB server can facilitate data exfiltration by encoding sensitive information within DNS queries. Since DNS traffic often escapes scrutiny from firewalls and intrusion detection systems, this approach presents a unique opportunity for attackers. The effectiveness of an OOB attack largely hinges on the egress firewall rules that dictate which outbound requests are permitted from the vulnerable system, alongside the configurations of perimeter firewalls.

1. Installing BIND on DNS Servers

Ensure your server is updated and install BIND using the following commands:

apt-get update
apt-get install bind9 bind9utils bind9-doc

2. Configuring the `named.conf.options` File

In the file /etc/bind/named.conf.options, configure the basic DNS settings:

options {
        directory "/var/cache/bind";
        recursion yes;               # Enable recursion for internal DNS lookups
        auth-nxdomain no;             # Prevent DNS poisoning by disallowing domain redirects
        forwarders {                  # Specify Google's DNS for external queries
                8.8.8.8;
        };
        forward only;
        dnssec-validation yes;        # Enable DNSSEC for added security
        querylog yes;                 # Log DNS queries for auditing
        listen-on-v6 { any; };        # Support IPv6 queries
};

3. Creating a DNS Zone File

Create the necessary directories and files for your DNS zone configuration. Replace example.com with your actual domain.

mkdir /etc/bind/zones
touch /etc/bind/zones/example.com

4. Configuring the Zone File for Your Domain

In the file /etc/bind/zones/example.com, define your DNS records. Replace <Your Server IP> with your actual server IP address and example.com with your domain name:

;
; BIND data file for example.com
;
$TTL    3h
@       IN      SOA     ns1.example.com. admin.example.com. (
                          1        ; Serial number, increment on every update
                          3h       ; Refresh interval
                          1h       ; Retry interval
                          1w       ; Expiration time
                          1h )     ; Minimum TTL
;
@       IN      NS      ns1.example.com.
@       IN      NS      ns2.example.com.
example.com.    IN      MX      10      example.com.
example.com.    IN      A       <Your Server IP>
ns1                    IN      A       <Your Server IP>
ns2                    IN      A       <Your Server IP>
www                    IN      CNAME   example.com.
mail                   IN      A       <Your Server IP>
ftp                    IN      CNAME   example.com.

5. Configuring the `named.conf.local` File

In the file /etc/bind/named.conf.local, link your zone file:

zone "example.com" {
       type master;
       file "/etc/bind/zones/example.com";
};

6. Checking the BIND Configuration Syntax

Validate your configuration before restarting the BIND service:

named-checkconf                      # Check named configuration syntax
named-checkzone example.com /etc/bind/zones/example.com   # Validate zone file
systemctl restart bind9              # Restart the BIND service

7. Creating & Configuring the Logging File

Ensure logs are stored for auditing and troubleshooting:

mkdir /var/log/named
touch /var/log/named/named.log
chown root:bind /var/log/named/named.log
chmod 777 /var/log/named/named.log

In the file /etc/bind/named.conf.options, add the logging configuration:

logging {
        channel default_log {
                file "/var/log/named/named.log";
                print-time yes;
                print-category yes;
                print-severity yes;
                severity info;
        };
        category default { default_log; };
        category queries { default_log; };
};

8. Final Steps

Restart the BIND service and monitor its status:

systemctl restart bind9
systemctl status bind9

9. Reading Logs in Real-Time

Monitor live logs to ensure everything is functioning as expected:

tail -f /var/log/named/named.log

Conclusion

Out-Of-Band techniques, especially when paired with DNS, illustrate a crucial aspect of cybersecurity: the need to understand both offensive strategies and defensive measures. This guide not only highlights the exploitation potential of OOB techniques but also emphasizes the importance of robust security practices to counteract such sophisticated attacks.

Spix0r/out-of-band-dns-bind-setup.md