What is DNS Cache Poisoning aka DNS Spoofing?

What is DNS Cache Poisoning?

DNS cache poisoning occurs when misleading information is entered into a DNS cache, causing DNS queries to return an inaccurate answer and users to be led to the wrong domains. DNS spoofing is another term for DNS cache poisoning.

  • IP addresses are the Internet's "room numbers" allowing web traffic to reach the correct destinations. DNS resolver caches serve as the "campus directory," and when they store incorrect information, traffic is routed to the incorrect location until the cached information is updated.

  • DNS spoofing is a threat that imitates real server destinations in order to redirect traffic to a domain. The purpose of many techniques of DNS spoofing attacks is to direct unsuspecting users to malicious websites.

  • DNS cache poisoning is a kind of DNS spoofing that involves your system storing the forged I.P. address in your local memory cache. This causes the DNS to remember the faulty site for you, even if the problem is rectified or never occurred on the server's end.

An assault against DNS spoofing can be carried out in a number of methods, including −

  • MITM attacks − Man-in-the-middle attacks include intercepting communications between users and a DNS server in order to redirect consumers to a different/malicious IP address.

  • DNS server compromise − A DNS server is directly hijacked when it is configured to return a malicious IP address.

How Does DNS Cache Poisoning Work?

For a set period of time, a DNS resolver will record the results to IP address inquiries. As a result, the resolver can answer subsequent inquiries significantly faster without having to negotiate with the several servers required in traditional DNS resolution. DNS resolvers keep responses in their cache for as long as the IP address's set Time to Live (TTL) permits them to.

By impersonating the DNS nameservers, sending a request to a DNS resolver, then faking the response when the DNS resolver asks a nameserver, attackers can poison the DNS caches.

DNS queries and answers employ User Datagram Protocol (UDP), instead of TCP, which needs both communicating parties to execute a 'handshake' to commence communication and authenticate the identity of the devices. In UDP, there's no way to know if a connection is open, if the recipient is ready to receive, or if the sender is who they claim they are. For this reason, UDP is subject to forging; an attacker may send a message through UDP and forge the header data to make it appear to be a response from a valid server.

To carry out DNS spoofing attacks, attackers must additionally know or predict a number of factors −

  • Which DNS requests aren't cached by the targeted DNS resolver, forcing it to ask the authoritative nameserver?

  • Which port does the DNS resolver use? Previously, they used the same port for every query, but now they use a different, random port each time.

  • The number assigned to the request.

  • To which authoritative nameserver will the inquiry be directed?

Because there is no way to check if the information is true and originates from a valid source, a DNS resolver accepts and caches fraudulent responses without question.

How You Can Protect Your DNS Server from Poisoning?

You may adjust the settings of your DNS server in addition to monitoring and analytics.

  • To avoid being poisoned by repetitive searches, keep them to a minimum.

  • Only save information about the requested domain.

  • Limit the answers to those that pertain to the specified domain.

  • Clients must be forced to utilize HTTPS.

In addition, you can use the following tools and methods to protect the DNS Server −

  • DNS spoofing detection tools − These tools, which are similar to endpoint user security solutions, scan every data received before sending it out.

  • DNSSEC (Domain Name System Security Extensions) − The DNSSEC system, which is essentially a DNS "confirmed genuine" mark, helps make DNS lookups valid and spoof-free.

  • End-to-end encryption − Encrypted data transferred for DNS queries and responses keeps thieves out since they can't duplicate the legal website's unique security certificate.