DNS Security: Prevent Hijacking and Spoofing Attacks

About 9 min read

DNS (Domain Name System) is the backbone of the internet, functioning as the "phone book of the internet" that translates domain names into IP addresses. However, DNS was not designed with sufficient security in mind when it was created in 1983, making it a prime target for attackers. According to Akamai's 2024 report, approximately 92% of malware communications pass through DNS, and attacks exploiting DNS continue to increase as of 2025. In particular, with the spread of DNS over HTTPS (DoH), DNS tunneling attacks that are difficult to detect with traditional network monitoring have emerged as a new threat. This article explains the major threats to DNS, how to choose a secure DNS service, and how to leverage filtering features.

How DNS Works and Its Vulnerabilities

When you enter a URL in your browser, a query is first sent to a DNS resolver, which returns the IP address corresponding to the domain name. This name resolution process is typically carried out over unencrypted plaintext UDP communication (port 53), creating a risk of interception and tampering by third parties along the communication path - a type of man-in-the-middle attack. A single web page load generates an average of 20 to 30 DNS queries, and the fact that each one is sent in plaintext is often overlooked.

The default DNS provided by your ISP (Internet Service Provider) is in a position to know every site you visit. From a privacy perspective, protecting DNS communication is important. It is worth noting that even when accessing HTTPS-encrypted sites, if the DNS query itself is in plaintext, "which sites you visited" is fully visible to third parties.

DNS Hijacking

DNS hijacking is an attack that tampers with DNS responses to redirect users to fake sites. It is carried out by attackers rewriting the DNS settings on routers or changing local DNS settings through malware. Despite entering a legitimate URL, users are redirected to phishing sites, risking theft of passwords and credit card information. Many home routers still have their admin panel passwords set to factory defaults, which is one of the main entry points for DNS hijacking. Change your router admin password to a strong one generated with passtsuku.com.

DNS Spoofing - Cache Poisoning

DNS cache poisoning is an attack that injects forged DNS records into a DNS resolver's cache. Once the resolver caches a forged record, all users relying on that resolver are redirected to fake sites. The Kaminsky attack discovered in 2008 exploited the design weakness that DNS transaction IDs are only 16 bits (65,536 possibilities), demonstrating the severity of this vulnerability to the world. Although mitigations such as source port randomization have been implemented, a fundamental solution requires the adoption of DNSSEC.

To deeply understand the technical background of DNS cache poisoning,DNS protocol and cache poisoning defense books (Amazon) is a helpful reference.

What Should You Actually Do?

Strengthening DNS security can yield significant results with just configuration changes. For beginners, simply changing the DNS settings on your router or device to Cloudflare (1.1.1.2) can block access to malware sites at the DNS level. For intermediate users, enable DNS over HTTPS (DoH) in your browser and change your router admin password to a strong one generated with passtsuku.com. For households with children, setting the router DNS to Cloudflare's 1.1.1.3 (malware + adult content blocking) protects all devices in the home without additional software.

How to Choose a Secure DNS Service

Support for Encrypted DNS Protocols

To protect DNS communication, choose a DNS service that supports DNS over HTTPS (DoH) or DNS over TLS (DoT). DoH encrypts DNS queries over HTTPS (port 443), making them indistinguishable from regular web traffic and thus difficult to intercept or censor. See the glossary entry on DoH for more details on how it works. DoT uses a dedicated port (853) to encrypt DNS communication with TLS. Which one to choose depends on your environment, but DoT is easier to manage in corporate networks, while DoH is less likely to be blocked by firewalls for personal use.

DNSSEC Validation

DNSSEC (DNS Security Extensions) is a mechanism that detects tampering with DNS responses by attaching digital signatures to them. Using a DNS resolver that supports DNSSEC validation can significantly reduce the risk of DNS spoofing. Cloudflare (1.1.1.1) and Google Public DNS (8.8.8.8) support DNSSEC validation. However, DNSSEC guarantees the authenticity of DNS responses but does not encrypt the communication itself. Privacy protection requires combining it with DoH or DoT. According to APNIC's survey (2024), the DNSSEC validation rate worldwide is only about 30%, and adoption is still in progress.

Checking the Privacy Policy

When choosing a DNS service, check the query log retention period and how the data is used. Cloudflare deletes DNS query logs within 24 hours and explicitly states that they are not used for advertising purposes. On the other hand, some free DNS services may use query data for advertising or marketing. A common misconception is that "free DNS is slow," but Cloudflare's 1.1.1.1 has an average response time of about 11ms according to DNSPerf measurements, which is faster than many ISP-provided DNS services.

Leveraging DNS Filtering

Blocking Malware Sites

DNS filtering is a technology that blocks domains of known malware distribution sites and phishing sites at the DNS level. When a browser attempts to access these domains, the DNS resolver returns the IP address of a block page or refuses name resolution. Cloudflare's 1.1.1.2 (malware blocking) and 1.1.1.3 (malware + adult content blocking) allow you to use DNS filtering without additional software. According to Cloudflare's published data, 1.1.1.2 blocks billions of requests to malicious domains per day.

Use in Home Networks

By changing the DNS settings on your router to a filtering-capable DNS service, you can apply filtering to all devices in your home at once. DNS filtering is a simple and effective way to enhance the safety of devices used by children. There is no need to install security software on each individual device, and all communications including IoT devices can be protected. Note that DNS filtering blocks at the domain level, so it cannot detect malicious content hosted on legitimate domains (e.g., malware placed on legitimate cloud storage). We recommend combining it with browser security features, firewall protection, and endpoint protection. When using devices outside the home, such as on public Wi-Fi, consider using a VPN to maintain DNS-level protection.

The Relationship Between DNS Security and Password Protection

The ultimate goal of DNS hijacking and spoofing is, in many cases, to steal user credentials. When users redirected to a fake login page enter their passwords, that information falls into the hands of attackers. By combining phishing protection with DNS security, you can significantly increase resistance to this type of attack. According to the Anti-Phishing Working Group (APWG) 2024 report, approximately 36% of phishing attacks target financial institutions, with DNS-based redirection being a primary technique.

As a defense-in-depth approach against this threat, combine the following measures. First, use a secure DNS service to prevent redirection to fake sites. Next, generate unique passwords for each service with passtsuku.com so that even if one password is compromised, the damage does not spread to other services. Additionally, set up two-factor authentication for important accounts to add a layer of defense that cannot be breached with passwords alone.

For design and practical methods of defense in depth,defense-in-depth and anti-phishing strategy books (Amazon) is also a helpful reference.

DNS security is a foundation for safe internet use, alongside password protection and phishing countermeasures. Start by checking the DNS settings on your router and devices, and consider switching to a service that supports encrypted DNS and filtering. On top of that, strengthening passwords for each service with passtsuku.com allows you to build a robust defense against both DNS attacks and password attacks.

What You Can Do Right Now

1. Change your router's DNS settings to Cloudflare's 1.1.1.2 (malware blocking) to protect all devices in your home
2. Change your router admin panel password to a strong one of 16 or more characters generated with passtsuku.com (leaving the default is dangerous)
3. Enable DNS over HTTPS (DoH) in your browser (Firefox: Settings → Privacy & Security → Enable DNS over HTTPS)
4. Set unique passwords for each service with passtsuku.com to prepare for phishing via DNS hijacking

Frequently Asked Questions

What types of attacks exploit DNS?

Common examples include DNS cache poisoning (injecting fake responses to redirect to malicious sites), DNS hijacking (altering DNS settings to intercept traffic), and DNS tunneling (hiding data in DNS traffic to bypass firewalls).

What is DNS filtering? Can individuals use it?

DNS filtering blocks access to dangerous domains at the DNS level. Individuals can use it for free by simply changing the DNS settings on their router or device to Cloudflare (1.1.1.2) or Quad9 (9.9.9.9).

What are the benefits of using DNS over HTTPS (DoH)?

DNS queries are encrypted, greatly reducing the risk of ISPs or third parties snooping on which domains you visit. It can be easily enabled in major browser settings and is especially effective for privacy protection on public Wi-Fi.