DNS hijacking interferes with or tampers with the domain name resolution process, redirecting users to unexpected network addresses. The core function of the DNS system is to translate human-readable domain names into computer-readable IP addresses. This process involves multiple layers: when a user enters a domain name into a browser, the operating system first queries the local DNS cache; if no record is found, it sends a request to a pre-defined recursive DNS server; the recursive server then iteratively queries the root name server, top-level domain server, and authoritative name server to finally obtain the target IP address. Every link in this query chain is vulnerable to attack, and attackers can hijack traffic by interfering with this process.

DNS hijacking primarily manifests in four technical forms. Local DNS hijacking occurs at the user device level, where malware modifies the system's hosts file or tamperes with the DNS server address in the TCP/IP configuration, redirecting the resolution of a specific domain name to a server controlled by the attacker. Router DNS hijacking targets network devices; attackers exploit weak passwords or vulnerabilities to infiltrate the router's management interface, modifying its DNS settings and affecting all devices connected to the network through that router. Man-in-the-middle attacks occur on the communication link between the user and the recursive DNS server. Attackers deploy fake Wi-Fi hotspots on public networks or conduct traffic monitoring and tampering on carrier networks. DNS cache poisoning attacks target recursive DNS servers, injecting fake domain name resolution records into the recursive server by forging response data from authoritative servers, causing a large number of users to be redirected.

The technical principle of DNS hijacking is based on the historical limitations of the protocol design. Traditional DNS queries use the connectionless UDP protocol, lacking encryption and authentication mechanisms. Attackers can easily forge source IP addresses and ports, sending a large number of forged response packets to the recursive server. Because early DNS protocols used a simple 16-bit transaction ID as the query matching identifier, attackers could brute-force guess or predict this ID value to make the recursive server accept forged responses. After receiving the forged responses, the recursive server caches them and distributes them to subsequent querying users, causing widespread and continuous impact. The following code simulates a simple DNS query process, demonstrating the transaction ID matching mechanism:

import socket
import struct
def send_dns_query(domain):
transaction_id = 0x1234
header = struct.pack('>HHHHHH', transaction_id, 0x0100, 1, 0, 0, 0)
question = b''.join([len(p).to_bytes(1, 'big') + p.encode() for p in domain.split('.')]) + b'\x00'
query_type = struct.pack('>H', 1)
query_class = struct.pack('>H', 1)
return header + question + query_type + query_class

DNS hijacking can be detected through technical means. Use the `nslookup` or `dig` command to query the same domain name but specify different public DNS servers (e.g., 8.8.8.8 and 114.114.114.114), and compare the returned IP addresses to see if they match. Visit known secure websites such as banks or government agencies to check if their SSL certificates are issued by trusted organizations; hijacking sites often use self-signed or invalid certificates. Deploy network monitoring tools to regularly test the resolution results of critical domains, establish a benchmark database of resolution results, and promptly detect abnormal changes. For enterprise users, detection capabilities can be enhanced by comparing internal and external network resolution results and monitoring non-standard port communication.

Addressing DNS hijacking requires deploying a multi-layered defense strategy. DNSSEC uses public-key cryptography to provide source verification and data integrity protection for DNS data, ensuring that resolution results have not been tampered with. Here is a basic example of configuring DNSSEC in BIND9:

zone "example.com" { type master;
file "/etc/bind/db.example.com";
key-directory "/etc/bind/keys";
auto-dnssec maintain;
inline-signing yes;
};

DNS-over-HTTPS and DNS-over-TLS protocols encrypt DNS queries during transmission, preventing man-in-the-middle eavesdropping and tampering. Enterprises should deploy dedicated DNS firewalls to filter malicious domains and abnormal resolution requests in real time. At the client level, ensure that operating systems and applications are updated promptly, install reliable security software, and avoid connecting to insecure public Wi-Fi. At the network device level, change the default management password of routers, disable unnecessary remote management functions, and update firmware regularly. For critical business systems, it is recommended to use hard-coded IP addresses or establish a local DNS resolution whitelist mechanism.

From an operations and maintenance management perspective, establishing a complete DNS security protection system requires comprehensive measures. Regularly audit the configuration and logs of all DNS servers and monitor abnormal query patterns. Redundant deployment of DNS infrastructure should be implemented to avoid single points of failure. Develop detailed emergency response plans for DNS security incidents, clearly defining the procedures for handling hijacking incidents. Strengthen employee cybersecurity awareness training and maintain open communication channels with ISPs to ensure rapid coordination and handling in the event of suspected large-scale hijacking.

With the widespread adoption of IoT devices and mobile internet, the attack surface for DNS hijacking continues to expand. Future defense technologies will focus more on end-to-end security, such as blockchain-based distributed DNS systems and anomaly detection algorithms incorporating artificial intelligence. While the deployment rate of DNSSEC is gradually increasing, its global coverage is still less than 30%, requiring collaborative efforts from the industry. For ordinary users, choosing a reputable DNS service provider, keeping software updated, and cultivating basic security awareness are the first lines of defense against DNS hijacking. Enterprise users, on the other hand, need to invest in building a layered DNS security architecture based on business importance, organically combining technologies such as DNSSEC, DoH/DoT, and threat intelligence to construct a reliable domain name resolution environment.