The Domain Name System (DNS) is the invisible workhorse that powers finding and accessing websites and other internet services. When you type a website URL into your browser, DNS is what translates the domain name into an IP address behind the scenes. Without DNS mapping domain names to IPs, the internet as we know it wouldn‘t function.
But like any critical technology infrastructure, DNS comes with its fair share of security vulnerabilities that attackers are eager to exploit. Given the foundational nature of DNS, a successful attack can wreak havoc on an organization. That‘s why it‘s so important for security teams to thoroughly test their DNS environments for risks and be ready to fix any weaknesses discovered.
In this comprehensive guide, I‘ll walk you through different methods to test the security of your DNS servers and configurations. I‘ll also explore proven fixes and best practices to harden your DNS security posture. Implementing DNS security checks and controls is essential to avoid becoming the next victim of cyber attacks abusing the vital DNS system.
Why Should You Care About DNS Security?
As an infrastructure technology that runs behind the scenes, it‘s easy to overlook DNS when considering potential security risks. But make no mistake – DNS vulnerabilities open doors for attackers to cause major damage. Flaws in DNS can be leveraged in many ways:
Traffic hijacking – Hackers redirect your traffic to fake, malicious websites to steal data.
Distributed denial-of-service (DDoS) – Your DNS servers are used to amplify DDoS attacks targeting others.
Domain hijacking – A hacker takes over your domain and directs it elsewhere.
Data exfiltration – DNS tunneling leaks your sensitive internal data.
These threats above are just a few ways attackers abuse vulnerable DNS servers. A 2022 survey conducted by the Cloud Security Alliance found that over 63% of organizations experienced a DNS attack within the prior two years. Clearly, DNS attacks are common and increasing.
Some real-world examples further demonstrate the damage of DNS hacks:
In 2022, threat actors redirected MyCrypto‘s DNS to phishing sites to steal crypto wallet funds from users.
The Russian hacking group CoomingProject hijacked multiple flight company domains in 2022 to conduct cyber espionage.
The 2021 Codecov software supply-chain attack utilized DNS manipulation to steal data from hundreds of tech firms.
Suffice to say, DNS is a prime target for modern hackers. Later in this article, I‘ll overview tools and techniques you can use to proactively test and secure your DNS before attackers get the chance. But first, let‘s explore how DNS works under the hood…
A Quick DNS Refresher
Before diving into DNS security testing, let‘s recap how DNS operates to provide name resolution that connects domain names to servers on the internet:
DNS uses a hierarchical distributed database to store domain records. This includes name servers (NS), IP addresses (A), and more.
When a client queries DNS to resolve a domain like example.com, the DNS resolver asks the root name server for the .com top level domain‘s (TLD) name servers.
The TLD name servers then respond with the example.com name servers. The resolver asks one of those name servers for the A record to get the destination IP address.
The DNS server responds with the IP address mapping for example.com to complete the name resolution.
This process relies on chain of trust. Each DNS server trusts that the servers above it in the hierarchy provided authentic data. But what if this chain of trust breaks? That‘s where DNS security vulnerabilities open the door to malicious misdirections and hijacking by attackers.
Now that we‘ve covered the importance of DNS security and basics of how DNS works, let‘s explore tools and techniques you can use to thoroughly test the security of your DNS…
Tools to Test DNS Security
Multiple open source and commercial tools are available to analyze your DNS infrastructure for risks. I recommend using a combination for the most comprehensive results. Here are some top options:
The dig command comes standard with many UNIX/Linux distributions and can check for some DNS security best practices like DNSSEC. Some useful tests:
$ dig example.com +dnssec # Checks if DNSSEC enabled $ dig ns example.com # Lists name servers for a domain $ dig axfr @ns1.example.com example.com # Tests for zone transfer allowed
Dnsrecon from Kali Linux performs DNS enumeration via zone transfers and other techniques. Look for any unauthorized info disclosure.
Nmap network scanner can find open recursive DNS resolvers using the dns-recursion NSE script. Hackers abuse these for DDoS.
DNSViz provides in-depth analysis and visualization of DNSSEC and other DNS features. It can detect configuration issues that impact security.
ImmuniWeb® DNS Audit
Commercial tools like High-Tech Bridge‘s ImmuniWeb® offer comprehensive DNS testing for security risks and compliance. ImmuniWeb® scans for 100+ DNS vulnerabilities across 10 key categories, prioritizes fixes, and provides detailed reporting.
Where to Check for Weaknesses
When testing DNS security, make sure to check these key areas for potential vulnerabilities:
Zone transfers – Should be restricted to prevent DNS data disclosure to unauthorized parties.
DNSSEC – Enables authentication of DNS data origin and integrity. Vulnerable if misconfigured or not implemented.
Open resolvers – Recursive resolvers open to the public are vectors for DDoS amplification attacks.
Subdomain hijacking – Stale subdomains can be taken over by attackers to compromise or impersonate.
Recursive resolvers – Improperly configured recursive resolvers are also prime DDoS targets.
Use a combination of manual spot checks and automated scanning tools to thoroughly inspect each of these critical areas for your DNS infrastructure – on both internal and external DNS servers.
Remediating Discovered Flaws
Once your comprehensive DNS security testing identifies areas needing improvement, you‘ll need to roll up your sleeves and get to fixing. Here are smart ways to address common vulnerabilities discovered:
Implement DNSSEC – Digitally sign records and enable validation to prevent spoofing and manipulation.
Restrict zone transfers – Only allow authorized slave name servers, not public access.
Close open resolvers – Disable recursion for externals. Use ACLs to limit access.
Monitor certificate transparency – Watch for unauthorized certificate issuance that may indicate domain hijacking.
Use registry/registrar locks – Protect domain ownership transfer and modification without approval.
Reassess DNS server placement – Don‘t expose resolvers to external networks unless absolutely needed.
Add DNS filtering – Inspect and filter DNS traffic to detect anomalies and block attacks.
Regularly testing your DNS infrastructure and promptly addressing any weaknesses found is crucial for keeping your organization‘s DNS secure. Don‘t give attackers the opportunity to hijack or weaponize your DNS servers!
The Takeaway on DNS Security
We covered a lot of ground looking at why DNS security matters, how to comprehensively test for risks, and the steps to fix issues discovered. The key takeaways for securing your organization‘s Domain Name System are:
DNS is highly vulnerable to multiple dangerous attack types like hijacking and DDoS amplification.
You need to regularly test your internal and external DNS servers for security flaws before hackers find them.
Use a combination of automated scanning and manual checks for the most complete results.
Quickly fix any weaknesses found by implementing DNSSEC, closing resolvers, monitoring certs, and more.
Keep testing and hardening DNS security to detect and stop threats before they cause serious business disruption.
By adopting proactive DNS security testing and remediation, you can identify and fix chinks in the DNS armor before cyber criminals exploit them to infiltrate networks, steal data, disrupt operations and tarnish reputations. DNS is too important to overlook when it comes to strengthening enterprise security defenses.
Hopefully this guide gave you tools and techniques to improve the security posture of your organization‘s Domain Name System against constantly evolving threats in cyberspace. Please share any other DNS security tips and tools I may have missed in the comments below!