How to secure DNS server?

dns-security-best-practices-oMost internet applications run on the basis of DNS then it may be emails, website browsing, messengers, etc. But very few detect the presence of this extensively used service. And this is the reason why the vulnerabilities in DNS service are ignored by server administrators resulting in easy exploitation by hackers.

Usually, securing a server involves server software plus application software security, file system security, physical and network security.

Below are steps to secure your DNS server –

Secure Your Server Information

Every server software has a defined version number. It’s quite easy for the attackers to identify the DNS server version from simple DNS lookup information, detect the vulnerabilities and attack the server.

If the software version information is hidden, the hacker would need to struggle to find it and attack the DNS server. This would surely make the attack impossible, preventing the DNS server.

Restrict Limitation on Recursive Queries

A DNS server handling the recursive queries forwards the DNS queries  to another DNS server in case there aren’t any records available. Excessive recursive queries can hamper the memory of your server.

Queries are accepted from all by an open DNS server and those can even contain malicious users that query the server.  DOS attacks and Cache poisoning are the results of accepting such queries.

Network traffic is possible to be restricted if too many requests are sent to the DNS server, further making it unresponsive.  Cache poisoning involves sending of specific queries to DNS server and controlling server traffic forcefully by attackers.

When a closed DNS server is configured, recursive queries can be limited as the server accepts queries only from the trusted clients. Restricting the client numbers served concurrently by the DNs server or turning off recursive queries can also be done.

Run the server as non-privileged user

If the DNS server is run as a privileged user like root, the attackers gaining access to it can easily track other processes too by misusing the privileges of the super-user account.

In order to avoid such a misuse, DNS server is mostly run as a non-privileged user. Now, even if the DNS server gets hacked, the hacker will get an access to DNS processes only and won’t be able to enter into other services.

Limit Zone Transfers

It is possible to transfer the DNS zones from the DNS server to other hosts by default. But this practice is considered to be highly insecure as it renders the zones that are public as well as vulnerable to attacks by hackers.

Therefore, there should be a limitation on DNS zone transfers to only certain trusted slave DNS servers and all other hosts need to be prevented from performing bulk transfers.

DNS Security Extensions (DNSSEC) Need to be Used

If an attackers takeovers the DNS lookup process, the user traffic can be redirected to their malicious site and it would be possible to save confidential information from users or display fraud results to them. In order to avoid such attacks, DNSSEC technology is used.

The DNS data validity is assured by digitally signing it in the DNSSEC technology. The DNS zones can be validated only by third-party signing authorities, like ICANN for the users to confirm its validity.

For the confirmation that users are connecting to the right DNS server and prevent DNS Spoofing, DNSSEC security extension deployment is essential.

Keep Your Server Always Updated

If any outdated software is running on your server, it is vulnerable to attacks. For example, the versions 4 and 8 of the BIND DNS software ate highly insecure and prone to attacks. This indicates that you should always keep your software updated.

New software versions that offer better security in comparison to previous versions need to be found and installed on the server for wading off the attackers. To get prompt updates, subscribing to software security updates and other security mailing lists would prove helpful.

Conclusion

Every month thousands of servers are been hacked or attacked due to software vulnerabilities. But if you protect your DNS server with these six practices mentioned here, the server will be strong enough to prevent any attacks.

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