What is DNS spoofing?
DNS spoofers know websites rely on trust to serve customers and ensure security. These malicious attackers seek to divert legitimate traffic to fake destinations, where they can harvest data and spread malware. Learn how spoofing operates and take action to secure your website.
DNS spoofing definition
DNS spoofing or DNS cache poisoning attacks redirect users to malicious websites by altering Domain Name System (DNS) caches. Attackers insert fake DNS records into a system’s cache, making it resolve domain names incorrectly. This lets them redirect users without detection, bypassing standard security defenses.
Manipulating DNS information allows attackers to direct traffic to malicious websites that seem identical to genuine versions. However, when users interact with fake sites, criminals can extract sensitive data or deliver malware to their devices.
How DNS spoofing works
DNS acts like an online version of street address directories, allowing traffic to flow between sites and enabling web users to move between servers located across the world.
DNS servers convert text-based web addresses into IP addresses that the user device and web server can understand. This process relies on a DNS resolver (generally maintained by the user's Internet Service Provider).
If the resolver's cache already holds the destination IP address, the DNS resolver directs traffic to the correct destination. If not, the resolver refers to a Top Level Domain server (TLD) to obtain a legitimate IP address from the destination nameserver.
DNS cache poisoning or "spoofing" targets DNS resolvers by swapping fake IP addresses for legitimate versions.
DNS poisoning works because resolvers generally cannot verify DNS address data. DNS requests are also vulnerable because they rely on User Datagram Protocol (UDP) transactions. UDP does not feature robust verification of DNS requests and headers.
Instead, they rely on timeouts to delete obsolete information. This system creates a vulnerability for attackers to exploit.
Attackers pose as legitimate DNS nameservers (servers that store website DNS records and convert them into IP addresses). IP spoofing sends requests to the target DNS server. When asked for identification, criminals use forged UDP headers to fool the DNS resolver into approving their request.
If the DNS server approves the request, attackers can redirect site users to wherever they choose until the DNS request times out.
Criminals must be very fast to pull off DNS cache poisoning attacks. The authentic nameserver will also respond milliseconds after the initial request. However, skilled threat actors leverage tiny windows of opportunity to achieve their objectives.
Risks linked to DNS spoofing attacks
DNS poisoning is a serious cybersecurity threat. Companies need measures to prevent spoofing attacks wherever possible.
Malware infection often results from DNS poisoning attacks. When users visit fake websites, attackers can implant Trojans or worms via malicious website code, download requests, or corrupted data entry forms. These agents can access network devices, leading to data breaches.
Malware infection often leads to secondary ransomware attacks, taking systems offline and putting data at risk.
In other cases, businesses risk losing traffic due to DNS poisoning attacks. Criminals can use DNS spoofing techniques to "steal" legitimate traffic. Attackers use spoofing to boost the ranking of malicious sites and make them more effective weapons in future projects.
Methods of DNS cache poisoning
DNS cache poisoning always manipulates DNS address data to redirect web traffic. The process above is the most common way to achieve this. However, several ways exist to access DNS resolvers and launch DNS spoofing attacks.
- Direct manipulation of DNS server records - Attackers use false nameservers to send DNS requests and respond before the genuine nameserver (as detailed above).
- DNS server hijacking - DNS poisoning attackers hijack the website's Domain Name System server and configure the DNS server to send false IP addresses.
- Extending Time-to-Live periods - Hijackers can also extend DNS timeouts, allowing fake DNS requests to survive longer. This makes attacks longer and enlarges the target community.
- Man-in-the-middle attacks on DNS nameservers - A DNS spoofing attack can intercept traffic between DNS servers and users. Attackers can then alter DNS responses to direct traffic to a malicious website.
- Brute forcing transaction IDs - DNS queries include limited space for transaction IDs. If servers rely on the same port for each response, DNS attacks can flood the DNS resolver with requests until they obtain a matching ID.
DNS poisoning attack example
Let's consider a case study to show how DNS poisoning works in the real world. In our example, a user wants to communicate with the web server of the eCommerce company retailer.com. The user IP address is (192.168.194.43) and the website address is (192.168.131.153).
Unknown to the user, a cyber attacker with the IP address (192.168.23.67) is waiting to intercept this communication channel.
- The attacker starts by fooling the retailer.com web server into thinking their IP address belongs to the genuine user.
- Next, the attacker works on the user side. They use spoofing tools to fool the user's device into thinking they are the retailer.com server.
- This creates a man-in-the-middle situation. The attacker can now divert all IP packets sent between the user and the web server to their device. This device becomes a server for a completely fake version of the retailer.com website.
- The final step involves diverting DNS requests to the attacker's host file and the fake website. Criminals can use publicly available tools like DNSspoof to complete the DNS poisoning process.
Tips to prevent DNS spoofing attacks
DNS spoofing is a significant network security threat to website owners and visitors. From the perspective of website owners, ways to prevent DNS poisoning include:
Use Domain Name System Security Extensions (DNSSEC)
The DNSSEC protocol is an updated set of DNS specifications that adds extra verification layers for each access request. Signatures based on public key cryptography verify the source and integrity of DNS records.
This helps prevent DNS poisoning by checking for tampering and creating a chain of trust within the domain name system. However, DNSSEC transactions are not fully encrypted and is not yet fully supported - although its use is rapidly spreading.
Enhance protection with trusted DNS servers
A trusted DNS server validates all DNS requests, checking the identity of the originating server. Trusted servers limit timeout durations, implement DNSSEC, and may include monitoring tools to detect suspicious DNS requests. Unlike basic DNS server designs, they also randomize ports and transaction IDs to make hijacking harder.
Encrypt connections between DNS resolvers and servers
Tools like DNSCrypt allow you to create encrypted connections between resolvers and servers. This dramatically cuts the likelihood of man-in-the-middle interceptions and ensures all DNS requests originate from trusted sources.
Implement robust network monitoring and security tools
Strong network defenses help identify cache poisoning attacks and limit their effects. Web Application Firewalls (WAF) analyze traffic to detect patterns associated with DNS spoofing attacks. Intrusion Detection Systems (IDS) monitor for attack signatures and deviations from baseline behavior.
Regularly update DNS software
Ensure DNS server firmware is updated and hardened against active DNS spoofing techniques.
The above measures will help you avoid malware infections and data breaches linked to malicious websites. Safeguard your web assets and prevent secondary attacks with robust DNS spoofing protection.