DNS (Domain Name System) is a fundamental protocol of the internet that translates human-readable domain names (like example.com) into machine-readable IP addresses (like 192.0.2.1).
It acts as the internet’s directory, translating domain names into IP addresses, making it essential for the web’s efficient operation. Unfortunately, this essential function also makes DNS an attractive vector for cybercriminals.
A DNS firewall is a vital defence mechanism that adds an extra layer of security by protecting against DNS-based attacks. This blog will explore what a DNS firewall is, how it works, and the benefits it offers to organizations.
What is a DNS Firewall?
A DNS firewall is a security solution that monitors and filters DNS queries, blocking malicious domains and preventing users from connecting to dangerous sites. By inspecting outgoing DNS requests, it ensures that attempts to access malicious or unauthorized domains are stopped before any damage can occur.
DNS firewalls act as the first line of defence by identifying and neutralizing threats that use DNS as an attack vector, such as phishing, malware, ransomware, and data exfiltration.
Key DNS-Based Threats
DNS-based threats exploit the inherent weaknesses of the system to disrupt services, steal data, or hijack connections.
DNS firewalls protect against various DNS-based attacks, including:
DNS Cache Poisoning
DNS cache poisoning, occurs when attackers inject malicious data into the DNS cache of a resolver. This malicious data alters the IP address associated with a legitimate domain, redirecting users to fraudulent websites or malicious servers.
DNS Tunnelling
DNS tunnelling is a sophisticated method used to exfiltrate data or control malware on a compromised system by encapsulating other types of traffic (e.g., HTTP or SSH) within DNS queries and responses. Since DNS traffic is often trusted and overlooked by firewalls, attackers can use it to sneak data through the network.
DNS Amplification (DDoS Attack)
DNS amplification is a type of Distributed Denial of Service (DDoS) attack in which attackers exploit the open nature of DNS to overwhelm a target with a large volume of traffic. Attackers use small DNS queries that result in much larger DNS responses, magnifying the impact of their attack.
DNS Hijacking
In a DNS hijacking attack, attackers alter DNS settings to reroute traffic from legitimate websites to malicious or fraudulent ones. This can be done by gaining control over a DNS server, router, or modifying a user’s local DNS settings.
DNS hijacking occurs when attackers alter DNS settings to redirect traffic from legitimate websites to malicious ones, often by gaining control over a DNS server, router, or modifying local DNS settings. This tactic can facilitate phishing attacks, where users are manipulated into revealing sensitive information by being redirected to fake websites that mimic legitimate ones.
Additionally, attackers may engage in malware distribution by using DNS requests to deliver malicious software, either through seemingly harmless requests or by redirecting users to sites that host harmful payloads.
DNS Flood Attack
A DNS flood is another type of DDoS attack targeting DNS servers specifically by flooding them with an overwhelming volume of requests. Unlike DNS amplification, which involves large response sizes, a DNS flood relies on sheer volume to overload the server’s ability to process requests.
DNS Rebinding Attack
In a DNS rebinding attack, attackers manipulate DNS responses to bypass a browser’s same-origin policy and access internal network resources, effectively using the victim’s browser as a proxy to send malicious traffic.
How Does a DNS Firewall Work?
At a high level, a Domain Name System firewall operates by intercepting DNS queries from users and determining whether they are safe, blocked, or redirected. Here’s a step-by-step breakdown of how it works:
DNS Query Monitoring: A key DNS firewall feature is query monitoring. When a user attempts to visit a website, their device sends a DNS request to resolve the domain name into an IP address. The DNS firewall inspects this request before it is forwarded to the DNS resolver.
Threat Intelligence: The DNS firewall is integrated with threat intelligence feeds that contain information about known malicious domains, IP addresses, and DNS abuse patterns. It cross-checks the domain being queried against these lists.
Filtering and Blocking: If the domain is flagged as unsafe (e.g., a phishing or malware site), the DNS firewall blocks the request. Instead of allowing the user to connect, the firewall either drops the query or redirects it to a safe page explaining the block.
Logging and Reporting: DNS firewalls maintain logs of blocked queries and generate reports that help administrators understand the nature of threats targeting the network.
Rate Limiting: To mitigate attacks that involve sending large numbers of DNS requests in a short time—such as DDoS attacks—DNS firewalls include rate limiting. This feature restricts the number of DNS requests a single source can send within a certain timeframe. When the limit is exceeded, the source’s traffic is blocked or throttled, preventing the attack from overwhelming the DNS infrastructure.
Domain Reputation Analysis: Some DNS firewalls incorporate reputation-based analysis. This DNS firewall feature dynamically evaluates the safety of domains before allowing access, providing an extra layer of security against emerging threats.
Benefits of Implementing a DNS Firewall
Organizations of all sizes can benefit from deploying a DNS firewall as part of their security architecture. Below are some notable advantages:
Proactive Threat Prevention: DNS firewalls stop threats at the earliest stage—before the connection to malicious domains is established, preventing further exploitation of vulnerabilities or data breaches.
Mitigation of Malware and Phishing Attacks: By preventing users from accessing harmful sites, DNS firewalls significantly reduce the risk of infection from malware, ransomware, and phishing.
Reduced Attack Surface: By filtering out unwanted traffic, such as attempts to connect to command-and-control servers, Domain Name Server firewalls limit the ways in which attackers can compromise an organization’s network. Explore the best practices to reduce attack surface.
Compliance Support: DNS firewalls can help organizations meet compliance requirements by blocking access to sites or services that may violate data privacy laws (e.g., GDPR) or internal policies.
Under GDPR Article 32, organizations must implement appropriate security measures to address risks. By preventing access to known malicious sites, DNS firewalls provide an essential layer of security that reinforces compliance with data protection standards. Check out the application security requirements in compliance standards here.
Attack Mitigation via Rate Limiting: By restricting the rate at which DNS queries are processed from any given source, rate limiting prevents volumetric attacks like DDoS from overwhelming the system, ensuring that legitimate traffic can continue to flow without disruption. Explore other best practices to prevent DDoS attacks.
DNS Firewall vs. Network Firewall: Key Differences
While both DNS firewalls and traditional firewalls aim to protect networks, they operate at different layers of the OSI model and address different types of threats.
DNS Firewall: Operates at the application layer (Layer 7), focusing on filtering DNS requests to block access to harmful domains before they are resolved. It is highly effective against DNS-based threats and malicious domains.
Network Firewall: Operates at the network and transport layers (Layer 3 and 4), inspecting traffic flows, protocols, and ports. While effective against broad types of attacks (e.g., port scanning, IP spoofing), traditional firewalls are not specifically designed to handle DNS threats.
Best Practices for Implementing DNS Firewalls
To maximize the effectiveness of a DNS firewall, organizations should follow these best practices:
Regularly Update Threat Intelligence: Ensure that your DNS firewall is using up-to-date threat intelligence feeds to stay current with the latest threats and trends in the cyber landscape.
Monitor DNS Traffic: Regularly review DNS firewall logs to identify patterns of attempted attacks and adjust filtering policies as needed.
Integrate with Broader Security Infrastructure: DNS firewalls should be part of a multi-layered security approach, integrated with endpoint protection, web application firewalls, and security information and event management (SIEM) systems.
Educate Users: Train employees on the importance of DNS security and how DNS firewalls work. This can reduce the likelihood of users attempting to bypass security policies or fall for phishing attempts.
Limitations of DNS Firewalls
While DNS firewalls offer significant benefits, they are not a silver bullet for all cyber threats. Some limitations include:
False Positives: DNS firewalls may occasionally block legitimate sites if they are erroneously flagged as malicious, which could disrupt business operations if not properly managed.
Bypass Techniques: Some sophisticated attackers may use techniques such as DNS over HTTPS (DoH) to bypass DNS firewall protections.
Limited Visibility: DNS firewalls only inspect DNS traffic, meaning other types of network traffic are not directly monitored. Therefore, organizations need additional layers of security to handle threats from other attack vectors.
The combination of DNS firewall and application-layer protection ensures that both network and application traffic are thoroughly monitored and filtered.
With AppTrana WAAP You can manage DNS, and application security from a single platform. AppTrana provides robust DNS management capabilities, including blocking DNS queries to known malicious domains and offering fine-grained control over DNS traffic.
