DNS is a critical component of any network infrastructure. It is responsible for translating domain names into IP addresses, making it a prime target for attackers. A compromised DNS server can lead to traffic redirection, data interception, service downtime, and severe reputation damage.

The main objective of securing DNS includes ensuring the secure exchange of data between DNS servers, protecting DNS queries, securing zone transfers, and controlling DNS updates. Strengthening DNS security is a foundational step in overall website and server protection, as discussed in SupportPro’s guide on improving website security

In this article, we explain one of the most effective DNS-hardening methods: securing DNS using chroot, along with essential configuration considerations. Before proceeding, ensure that you have taken a full backup of your existing named.conf file.

Why Securing DNS Matters

Unsecured DNS servers are vulnerable to:

• Cache poisoning attacks

• Unauthorized zone transfers

• DNS amplification and DDoS attacks

• Data leakage and service disruption

Proper DNS hardening helps mitigate these risks and plays an important role in overcoming broader cloud and infrastructure management challenges

Securing DNS Through Chroot

Chroot is a powerful mechanism that limits the DNS service to a restricted directory, commonly known as a chroot jail. Even if the DNS service is compromised, the attacker’s access remains confined, significantly reducing the potential damage.

The chroot() function uses a system call that changes the apparent root directory for the running process, isolating it from the rest of the system.

a) Configuring the chroot Directory

While configuring the chroot environment, ensure that most of the directory structure is not writable by the named process. This prevents unauthorized changes.

Restricting write permissions is a fundamental step in server hardening, regardless of whether you are running Debian or CentOS-based systems

b) Copy Required Configuration Files and Zone Files

Existing named.conf and zone files must be moved into the chroot jail so that BIND can access them.

• named.conf→ /chroot/named/etc

• Zone files → /chroot/named/etc/namedb

Example:

cp -p /home/abc/bind/etc/named.conf /chroot/named/etc/ cp -a /home/abc/bind/var/named/* /chroot/named/etc/namedb/

For tighter security, BIND should not have write access to the main namedb directory. However, if your DNS server acts as a slave, it must be able to update zone files. In that case, create a separate directory with controlled write access.

chown -R named:named /chroot/named/etc/namedb/slave

c) Copy Shared Libraries

In addition to the named and named-xfer binaries, all required shared libraries must be copied into the chroot environment.

Use the ldd command to identify required libraries:

ldd /usr/sbin/named

Copy each listed library into the corresponding directories inside the chroot jail. Missing libraries can cause the DNS service to fail at startup.

d) Create Required Device Files

Some device files are required for normal DNS operation. For example, /dev/null must exist inside the chroot environment.

cd /var/named mkdir dev chown root:daemon dev chmod 111 dev mknod dev/null c 2 2 chown root:wheel dev/null chmod 666 dev/null

This ensures that DNS processes function correctly without exposing the entire system.

e) Copy Other Configuration Files and Restart Service

Create the /var/named/conf directory and copy the named.conf file from /etc into it. Once all files are in place, restart the named service to apply the changes.

systemctl restart named

Always verify DNS functionality using tools like dig or nslookup after restarting.

Long-Term DNS Security Best Practices

Chroot alone is not enough. For long-term DNS security:

• Restrict zone transfers using ACLs

• Enable DNSSEC where possible

• Monitor logs for unusual query patterns

• Automate configuration checks using deployment automation

• Conduct regular audits with experienced administrators or a reliable dedicated support team

Conclusion

Securing DNS is not optional it is a core requirement for a stable and trustworthy network. Implementing chroot significantly reduces attack surface by isolating the DNS service from the rest of the system. When combined with access controls, monitoring, and automation, it forms a strong foundation for DNS security.

If you require assistance implementing or auditing DNS security, contact SupportPRO Server Admin for expert support and proactive server management.