If you access a website directly by entering its domain name, a malicious DNS resolution process could redirect you to a carefully crafted, phishing website, even if the URL is entered correctly. This type of attack is called DNS spoofing or DNS hijacking, a silent "digital kidnapping" that leaves users and businesses unaware of data breaches or financial losses. Understanding its principles and building effective defenses is crucial for anyone who values ​​cybersecurity.

DNS spoofing succeeds because of a design flaw in the traditional DNS protocol—the lack of mandatory authentication and encryption. When your device needs to access a website, it first sends a query to a pre-configured DNS server (usually your internet service provider or a public DNS like 8.8.8.8). This query and response process is in plaintext by default and relies on a simple match of the query ID and port to verify the legitimacy of the response. By sniffing or predicting this information on the network, an attacker can send a forged response packet pointing to a malicious IP address to your device before the real DNS server does. Once your device accepts this preemptively arrived false answer, all access to that domain name before the cache expires will be redirected to a server controlled by the attacker. This fake website might look exactly like your target bank's login page, its purpose being to steal your account password.

DNS spoofing can be carried out in several ways. The most common is a combination of ARP spoofing and DNS spoofing within a local area network (LAN). The attacker first broadcasts fake ARP packets on the local network (such as public Wi-Fi), impersonating the network gateway. Subsequently, network traffic from all devices on the LAN flows through the attacker's machine, allowing them to easily intercept and tamper with DNS queries. Another method is direct router hijacking. Many home or small office routers have weak management passwords or have never been changed. Once an attacker compromises the router, they can directly modify its built-in DNS server settings, pointing them to a malicious DNS server, thus affecting all devices connected to that router. More covert and widespread is the man-in-the-middle attack, where attackers eavesdrop and tamper with any node in the communication path between your device and the DNS server. This can occur on insecure public networks or on compromised network devices. Furthermore, directly compromising or polluting a carrier's recursive DNS servers is a more upstream and far-reaching attack, potentially affecting a large number of users in a region.

Faced with these threats, deploying effective technical defenses is the first line of defense. The core solution is to use encrypted DNS protocols, which ensures that the query process is not eavesdropped on or tampered with. DNS-over-HTTPS and DNS-over-TLS are currently the mainstream standards.

DNS-over-HTTPS wraps DNS queries in an encrypted HTTPS connection, making it indistinguishable from ordinary web browsing traffic and effectively preventing interference along the path. Mainstream browsers such as Firefox and Chrome already support DoH. You can enable it by entering `about:config` (Firefox) in the browser address bar and searching for `network.trr` related configurations, or by enabling the "Use Secure DNS" feature in Chrome's "Security" settings. An example of using `curl` in the Windows command line to query a domain name through Cloudflare's DoH service is as follows:

curl -H "accept: application/dns-json" "https://1.1.1.1/dns-query?name=example.com&type=A"

DNS-over-TLS, on the other hand, uses the TLS encryption standard at the transport layer to protect DNS queries. It's better suited for global configuration at the operating system or router level. For example, on a router that supports DoT, you can set the DNS server to `tls://dns.google` or `tls://1.1.1.1`.

DNSSEC is another crucial security extension. It adds a public-key cryptographic digital signature to DNS responses, allowing your device to verify that the response truly comes from the authoritative administrator of the domain and has not been tampered with during transmission. While DNSSEC deployment relies more on domain owners and recursive DNS servers, you can benefit by choosing a public DNS resolver that supports and verifies DNSSEC, such as Cloudflare or Google's public DNS.

Besides technical measures, good security habits are equally important. The following daily practices can significantly reduce risk:

1. Use public Wi-Fi with caution: Avoid performing highly sensitive operations such as logging into bank accounts in places like cafes and airports. If necessary, always use a reliable DNS server with encryption enabled, or use a reputable service to encrypt all network traffic.

2. Strengthen home network devices: Immediately change the default management password of your home router and ensure its firmware is up-to-date. In the router settings, manually set the DNS server to a reliable public DNS, such as Cloudflare's `1.1.1.1` and `1.0.0.1`.

3. Keep operating system and software updated: Install security patches promptly to fix potential exploitable vulnerabilities in your local network protocol stack.

4. Pay attention to browser security warnings: Modern browsers are very clear about warnings for HTTPS website certificate errors (such as certificate-domain mismatch or certificates issued by untrusted organizations). If you encounter such warnings, stop accessing the site immediately.

For enterprise network administrators, the defense needs to be more layered. In addition to deploying next-generation firewalls that support DNS traffic inspection and filtering at the perimeter, consider enforcing DoH/DoT internally and deploying a dedicated internal DNS resolver to log and analyze all query requests to quickly detect abnormal patterns.

In conclusion, DNS spoofing is a highly dangerous and relatively insidious network attack. The key to addressing this lies in understanding that it exploits a lack of trust in fundamental internet protocols. Therefore, from individual users to enterprise administrators, actively embracing and deploying next-generation encryption and authentication technologies such as DNS-over-HTTPS, DNS-over-TLS, and DNSSEC is the only way to fundamentally strengthen this vulnerable link.