DNS hijacking is a type of cyberattack. This common method involves intercepting DNS query responses and returning incorrect IP addresses when a user attempts to access a specific domain name, redirecting the user to an unexpected website. DNS hijacking not only impacts user experience but can also lead to sensitive information leakage, financial losses, and malware infection.

How DNS Hijacking Works and Types

DNS (Domain Name System), a fundamental internet service, converts human-readable domain names into machine-readable IP addresses. The standard DNS resolution process consists of two phases: recursive and iterative queries. The user's device first sends a query to a local DNS server. If the local server doesn't have a cached record, it queries the root, top-level, and authoritative DNS servers, ultimately obtaining the correct IP address.

DNS hijacking can be categorized into the following types: local DNS hijacking involves infecting the user's hosts file or modifying DNS settings to implement redirection; router DNS hijacking exploits router vulnerabilities or weak passwords to change DNS configurations; man-in-the-middle attacks intercept and tamper with DNS responses during network transmission; and malicious DNS servers completely control the entire resolution process. Furthermore, there are DNS cache poisoning attacks, in which attackers inject forged resolution records into DNS servers, affecting all users of the server.

The Dangers and Impacts of DNS Hijacking

DNS hijacking poses a serious security risk. Attackers can create phishing pages that closely resemble the target website, tricking users into entering sensitive information such as login credentials and bank account details, leading to identity theft and financial fraud. Hijacking can also be used to push malicious ads or force specific content, disrupting the user experience and potentially spreading malware. Even more dangerously, attackers could redirect software update requests to malicious servers, distributing malware-bundled software update packages.

For enterprises, DNS hijacking can lead to the leakage of trade secrets, service disruptions, and damage to brand reputation. Some advanced persistent threat (APT) attacks even use DNS hijacking as an initial intrusion vector to gradually infiltrate the enterprise intranet and obtain critical data.

Technical Methods for Detecting DNS Hijacking

DNS hijacking can be detected through a variety of technical means. Comparing the resolution results from different DNS servers using the nslookup or dig command is the most basic method:

nslookup example.com
nslookup example.com 8.8.8.8

If a public DNS (such as 8.8.8.8) returns different results than your local DNS, it's likely a hijack. Online DNS testing tools, such as Google's DNS Diagnostic Tool, can also help identify anomalies. Network traffic analysis tools, such as Wireshark, can capture DNS requests and responses to check for abnormal TTL values ​​or non-authoritative responses.

For enterprise environments, deploying DNSSEC (DNS Security Extensions) validation is an effective detection method. DNSSEC ensures the authenticity and integrity of DNS responses through digital signatures:

dig example.com +dnssec

The "ad" flag in the returned result indicates successful validation. Regularly monitoring DNS query logs can also identify unusual patterns, such as a sudden increase in resolution failures or queries for uncommon domains.

Protection and Solutions

Personal user protection begins with using a trusted public DNS service. We recommend using services with security features, such as Google DNS (8.8.8.8, 8.8.4.4), Cloudflare DNS (1.1.1.1), or Quad9 (9.9.9.9). The method for modifying DNS settings varies depending on your operating system:

Windows:

Set-DnsClientServerAddress -InterfaceIndex <index> -ServerAddresses 8.8.8.8,8.8.4.4

Linux (NetworkManager):

nmcli con mod <connection name> ipv4.dns "8.8.8.8 8.8.4.4"

It's also crucial to ensure your router's administrator password is strong and to regularly update its firmware. Installing reliable security software can detect and block most local DNS hijacking attempts. Browser extensions like DNSSEC Validator can provide real-time protection.

Enterprise-level protection requires a more comprehensive strategy. Deploy DNSSEC on all authoritative DNS servers to provide cryptographic signature verification for domain name resolution. Implement DNS over HTTPS (DoH) or DNS over TLS (DoT) to encrypt DNS traffic and prevent man-in-the-middle attacks:

DoH configuration example (Unbound recursive server):

yaml
server:
tls-cert-bundle: "/etc/ssl/certs/ca-certificates.crt"
forward-zone:
name: "."
forward-tls-upstream: yes
forward-addr: 8.8.8.8@853dns.google

Network segmentation and firewall rules should restrict DNS traffic to only those originating from authoritative servers. Real-time monitoring systems should detect unusual DNS patterns, such as a high number of NXDOMAIN responses or queries for unknown domains. Regular security audits and penetration testing can help identify potential vulnerabilities.

Emergency Response and Recovery

Implement containment measures immediately upon confirmation of DNS hijacking. Isolate the affected device or network segment to prevent lateral movement. Reset the DNS settings of all relevant systems and clear the DNS cache:

Windows:

batch
ipconfig /flushdns

Linux:

systemd-resolve --flush-caches

Check and repair the hosts file, removing any abnormal entries. Change the router administrator password and perform a factory reset. Perform a full system scan to remove malware. For enterprise environments, rotate all potentially compromised credentials and keys, check system integrity, and update security policies.

Afterward, conduct a thorough forensic analysis to determine the attack entry point and scope of impact, and refine monitoring strategies to prevent recurrence. Keep all systems and applications up to date and patch known vulnerabilities promptly.

Protecting against DNS hijacking requires a multi-layered approach and continuous monitoring. By combining technical solutions, security awareness education, and a robust security policy, users can significantly reduce the risk of DNS hijacking and ensure secure and reliable network connections. As attack techniques continue to evolve, protective measures must be regularly evaluated and updated to address new threats.