What is DNS Filtering?

DNS filtering is a widely popular network security solution, particularly among home users and small and medium-sized businesses. While it is a low-cost, easy-to-manage technology that provides good protection against some kinds of cyber assaults without needing specific hardware, it is not a comprehensive security solution. It offers just a basic degree of protection and should be supplemented with other security measures like anti-virus, intrusion detection and prevention (IDS/IPS), application control, logging, reporting, and analytics.

This article will address the following questions. What is DNS filtering and how it works? Is it safe to use a DNS filtering solution exclusively in your home or business network? What are the DNS filtering method's flaws? How are attackers able to damage or get access to your important assets that are secured by a DNS filter?

What is DNS?

Before delving into the DNS filtering solution in detail, it's necessary to understand the Domain Name System, one of the essential technologies upon which the Internet is built. The Domain Name System, or DNS, is used to map domain names such as sample.com to IP addresses such as 155.176.198.234. DNS is required to enable people to visit websites without remembering complicated sets of numbers, much as a person may save the phone numbers of his friends in his mobile phone contacts list rather than memorizing each phone number.

This means that before your device can access information on a website or an online application, it must first get the IP address via a process known as DNS resolution. DNS resolution is the process by which your device receives the IP address of the server to which it is attempting to connect.

It begins by submitting a DNS query to the DNS resolver, a service that converts domain names to IP addresses. The DNS resolver either searches up the domain name and returns the IP address associated with it, or it queries other DNS servers.

DNS resolvers maintain a cache of queries and IP addresses to expedite domain resolution.

The domain gets resolved after your device obtains the right IP address.

When a user enters a website or a web application, the process of loading the content begins only when the user's device determines the right IP address. DNS is a necessary component of web content access. No material can be loaded until the DNS process completes. As a result, DNS filtering is an efficient method of exerting control over the material that users may access.

What is DNS Filtering?

DNS filtering is a method that enables you to restrict particular websites from being accessed for a specific reason, most typically based on their content. Initially, the technique was intended to assist in defending against spam and phishing attempts by blocking known suspect IP addresses. Today, it is used for a number of purposes: some individuals use it to protect against piracy, while others use it to block workplace access to contaminated or addictive websites (such as gambling). If a site, or group of sites, is regarded to be a danger, its IP address and access to it are restricted using a DNS filter.

A DNS filtering solution may enhance your cybersecurity capabilities by defending against most of the malware, ransomware, and phishing attacks at the DNS layer. It prevents your users from seeing objectionable or improper material, such as pornographic websites and time-wasting streaming videos. This protects corporate data and enables businesses to maintain control over what their workers may access through corporate networks. DNS filtering is often used in conjunction with a broader access control strategy.

Features of DNS Filtering Systems

All DNS filtering systems have the following two main functionalities:

• Blacklisting: A blacklist, also known as a blocklist, is a list of known malicious domains or IP addresses. DNS filtering systems may use publicly available blocklists, develop their own blocklists, or do both. There are several DNS blocklists, each with a distinct purpose. For instance, several blocklists are devoted to hazardous websites, phishing websites, and even botnets. Certain DNS filters will even automatically assess websites and add them to a blocklist. For example, if malicious code is discovered running on useful.com, the domain will be put on the blocklist.

  DNS filtering may also blacklist domains that are not used for malware or phishing attempts but do contain prohibited or unsuitable material. For instance, a business may seek to include adult-content-hosting websites in its DNS filtering blocklist.

• Whitelisting: Whitelist, also known as an allowlist, is the inverse of a blocklist; it is a list of DNS requests that are known to be safe. The whitelisting feature gives you more control over the list of sites that workers are permitted to view. It provides a list of permitted domains or IP addresses. Ascertain that workers have access to the websites they need for their jobs.

DNS filtering solutions available in the market may offer the following features too:

• Block sites that are considered suspicious, spam, spyware, malware, phishing, botnet
• Blocks annoying and spammy ads
• Browsing protection
• Privacy protection
• Parental control
• Banking security
• Identity protection
• Limits internet time
• Ability to monitor browsing habits
• Review what user has been browsing throughout the day
• Tracks browsing behavior
• Tracks device location
• Ability to turn the internet off during bedtime or when studying

How Does DNS Filtering Work?

DNS filtering system's basic function is straightforward: It acts as a gateway between the web server and you, ensuring that your browser does not recognize the blocked IP address and thus is unable to access the website. Let's deep dive into the DNS filtering mechanism.

All DNS requests are routed via a DNS resolver. DNS resolvers configured specifically for filtering may also operate as filters by refusing to resolve requests for specified domains listed in a blocklist, preventing users from accessing such sites. Additionally, DNS filtering services may use an allowlist rather than a blocklist.

The DNS filter will typically employ one of two setups to permit or restrict access:

• Blacklist: Also known as a "Block list," this system operates on the principle of "allow all except". Unless it is included in the list, every website is accessible. This list may be updated in the future based on internal or external threat information.

• Whitelist: Also known as an "Allow list", this method works on the idea of allowing access to only websites that have been expressly recognized as acceptable. The list may be generated manually or as a result of a mix of automatic and human inputs.

When the right DNS filters are in place, whenever a user requests a domain name, the DNS filter converts the entry to its IP address and compares it to the established rules.

DNS filtering may be used to blacklist or whitelist online sites based on their domain name or IP address:

• IP address: DNS filtering can also be implemented at the network level by blocking access to IP addresses that are associated with malicious websites. This is done by configuring the DNS server not to resolve the DNS queries for those IP addresses. This method may prevent access to a malicious website even if the DNS query is not conducted via a DNS resolver. However, it may be more difficult to maintain since IP addresses vary over time.

• Domain: The DNS resolver does not attempt to resolve or seek up IP addresses for specific domains. It will provide an error message informing the user that the website has been banned.

Assume one of your employees gets a phishing email and is duped into clicking a link to a malicious website, such as harmfulsite.com. Before loading the page, the user's computer makes a query to your DNS resolving service, which employs DNS filtering. If the harmful website is included on your blocklist, the DNS resolver will deny the request, preventing harmfulsite.com from loading and thereby defeating the phishing attack.

Figure 1. How DNS Filtering Works

Why Do You Need DNS Filtering?

Mistakes may happen, no matter how many cybersecurity protections you implement and how much awareness training you provide your workers. A company's default level of cybersecurity may be improved via effective filtering. Although it's impossible to prevent every dangerous website from being accessed since bad actors are continually generating new websites that haven't been examined and tagged, the great majority of risks may be prevented by deploying a DNS filtering solution.

DNS filtering may also be used to prevent unauthorized users from accessing particular types of websites on your network, whether this is for regulatory or productivity reasons. When you set up an acceptable use policy (AUP), you may prohibit your network users from accessing everything from gaming sites to social networking and adult content websites.

Your firm may be subject to cybersecurity requirements if it creates, stores, processes, or otherwise comes into touch with sensitive data. Regulatory agencies may demand comprehensive DNS content filtering directly, or it may be considered a recommended practice for compliance.

For instance, if your organization deals with HIPAA-covered protected health information (PHI), you'll need to install firewalls and filters to prevent unauthorized use and disclosure of PHI. Alternatively, if your business processes credit card transactions or cardholder data (CHD), you must set firewalls and web filters following the PCI DSS standard. Also, in the United States, schools and libraries must comply with the Children's Internet Protection Act (CIPA) to qualify for E-rate savings and government subsidies.

What are the Advantages of DNS Filtering?

There are numerous benefits of adopting DNS filtering on your network:

The primary advantage of DNS filtering is its simplicity. It does not require advanced security knowledge to install and manage. A DNS filter may be set up by even novice home users on their devices in just a few minutes.

Another reason why people prefer DNS filtering solutions is that they are one of the cheapest security products on the market. There is also an open-source variety of DNS filtering software that provides effective protection for free, such as AdGuard or pfBlockerNG.

You do not need to purchase an expensive and powerful appliance to operate one because the DNS filtering system is not resource-intensive. Using a DNS filter, you can quickly and affordably deploy a content filtering system for your home or workplace.

Additionally, higher employee productivity is an advantage of DNS filtering for companies. In addition to being a guaranteed source of infection, destinations such as peer-to-peer streaming sites may exhaust bandwidth and distract employees. When DNS filtering rules are configured to block time-wasting websites, company owners regain control of their networks.

Another advantage of the DNS filtering service is that it has low latency. DNS filtering does not degrade internet speed since all filtering occurs at the DNS lookup step of a web request before any content is downloaded. Filtering happens in the same amount of time as a typical DNS lookup, ensuring that there is no delay. With low latency DNS filtering, you may enjoy all of the advantages mentioned above without any delay in visiting secure websites.

In summary, by implementing a DNS-based web filtering service, you can:

• Create a safe and secure surfing environment for your users

• Block access to fraudulent and potentially dangerous websites

• Detect and prevent malware downloads

• Increase productivity by preventing users from connecting to the internet productivity drains

• Prevent users from accessing improper websites

• Ensure that compliance violations are minimized.

What are the Weaknesses of DNS Filtering?

DNS blocking may be a simple and cost-effective method of preventing employees from accessing harmful or undesired websites, with no overhead and no physical hardware required.

Cybercriminals, on the other hand, are always creating new and innovative strategies and techniques for gaining access to valuable assets and sensitive information on the Internet. In fact, this should keep you up at night if you rely just on DNS filtering for your cybersecurity, without other layers of protection like application control, IDS/IPS, and so on. In this section, we will explain the weaknesses of DNS filtering listed below:

• Recent Website-based Attacks

• DNS Evasion

• Poor or Lack of Manageability, Portability, and Flexibility

• DNS Vulnerabilities

• Poor or Lack of Reporting and Analytics

Recent Website-based Attacks

DNS filtering may assist in preventing malware, or malicious software, from invading company networks and user devices. Additionally, it may aid in the prevention of some types of phishing attacks. These capabilities, however, are contingent upon the DNS filtering system correctly classifying rogue IP addresses or domains as harmful. While DNS filtering may help prevent this malicious behavior, attackers create new domains at a breakneck pace, making it impossible to blocklist them all.

DNS Evasion

DNS filtering restrictions can be bypassed by clever users or because of an administrative error. Admins may temporarily remove the block in certain situations or even forget to re-enable blocking. Also, a curious employee may, however, create a proxy server or even alter DNS settings on a local level in order to get access. Proxy servers and anonymizer websites may be used to conceal traffic and circumvent the DNS filter. The second critical method of evading a DNS filtering service is to modify the DNS settings locally. Individuals with enough determination may be able to circumvent DNS filtering.

Manageability, Portability, and Flexibility

Even though installing and managing a DNS filtering system for a home user seems to be straightforward, this is not the case when network infrastructure grows in size and complexity by distinguishing the kinds of devices with varying needs, such as in business networks.

If your firm is still in the early phases of cybersecurity development, one of the smaller-scale techniques for DNS filtering may be sufficient for your present requirements. However, with time, you're likely to confront quickly expanding hazards that make maintaining DNS content filtering excessively difficult for your staff.

Furthermore, most DNS filtering solutions either lack integrations with third-party security systems or have weak integrations, which results in their failure to meet a business need.

DNS Vulnerabilities

One of the most serious assaults that DNS filtering cannot prevent is DNS spoofing, which provides an IP address that is not that of the intended website but a hostile website. DNS spoofing attack happens when DNS request information is altered to drive end users to a bogus website meant to deceive them into entering their login credentials. Numerous websites also download malware on the user's device, allowing hackers to get long-term access.

Additionally, DNS services are vulnerable to DNS tunneling and DNS hijacking attacks. DNS tunneling hides and transmits malware through SSH, TCP, or HTTP. DNS hijacking redirects DNS traffic to a separate domain name server that contains erroneous information designed to drive clients to malicious websites.

Poor or Lack of Reporting and Analytics

Because they rely on DNS services, almost all DNS filtering systems can only give limited network visibility due to the nature of their solutions. DNS filtering solutions can only show you what is going on in your network from a single point of view, which is limited. It is unable to give you thorough and overall visibility.

Conclusion

The simplicity, efficiency, and cost-effectiveness of DNS filtering solutions make them very popular in the IT security world, especially for home networks. Although they block the vast majority of harmful websites, none of the DNS filtering systems can block all harmful websites, since this requires determining if a webpage is dangerous. When a malicious actor launches a brand-new phishing website, verification and inclusion on a blacklist take time. As a result, a DNS filter may help mitigate danger, but can not eliminate it.

Most importantly DNS Filtering method has critical vulnerabilities and may be easily evaded by bad guys. Your curious users may bypass the filtering process by putting your network at risk. Also, cybercriminals have the ability to monitor a user's DNS requests and redirect them to malicious websites. DNS hijacking. DNS tunneling, DNS poisoning, DNS over HTTPS, or DNS over TLS are a few of the cyber threats that you'll have to deal with if you're using DNS filtering, and you'll have to use extra security measures to cope with them.

As a result, DNS filtering solutions cannot offer full network security on their own, they should be used in conjunction with next-generation firewalls as an extra layer of protection following the defense-in-depth strategy. It should never be regarded as an Enterprise-Grade Security Mechanism. Rather it's regarded as a complementary mechanism as an additional layer of security, which in reality you can find embedded in all modern NGFWs.

If you are looking for an alternative solution for DNS filtering systems or an additional security solution behind your DNS filtering mechanism, we strongly recommend Zenarmor next-generation firewall. It is a fast, powerful, cost-effective solution and easy to install. It provides not only the security level offered by DNS filtering systems but also rich reporting and analysis capabilities, a massive real-time cyber threat intelligence database, better manageability, and flexibility. It employs its technology to continuously improve its threat detection skills and to respond quickly to new cyber attacks. You can try Zenarmor Free Edition for free forever in a non-commercial environment.