DNS

What is DNS?

The abbreviation DNS stands for Domain Name System. The technology converts human-readable domain names into IP addresses, which in turn can be processed by clients and DNS servers. The DNS thus serves as the "telephone book of the web", as it is a directory that enables users to access the corresponding IP address of the associated web server via a specific URL using a browser.

The basic concept of the DNS dates back to the early days of the internet, when there was no cybercrime, tracking or digital censorship. This is why encryption methods were not used for the transmission of DNS queries back then. By default, the transmission was unsecured and in plain text. Today, cyber criminals exploit this vulnerability for DNS attacks. Specially hardened DNS servers, DNS extensions and encrypted DNS protocols provide a remedy.

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DNS: A Definition

The DNS is a globally distributed hierarchical directory service that is used to assign domains to the corresponding IP addresses on the Internet. DNS services can be used to assign domain names such as myrasecurity.com to a specific IP address of the web server. Before the introduction of DNS, domain information had to be stored and managed in the hosts file on each individual client. In favour of better scalability, Paul Mockapetris designed the DNS in 1983 with the standards RFC 882 and RFC 883.

The delegation of queries via the UDP protocol (User Datagram Protocol) is performed unencrypted in plain text in the DNS; the DNS entries are not verified. This makes the name assignment fundamentally vulnerable to external attacks, manipulation, monitoring or censorship. Both clients and DNS infrastructures accessing the DNS and organisations that become the target of a DNS-based overload attack are affected by these risks.

02 – What Types of DNS Servers Are There?

Various servers are used at different points for the Domain Name System. They are organised hierarchically and regulate the delegation of requests and responses.

DNS Root Server

The root servers of the DNS are responsible for the top level domains (TLD). As the highest authority in the hierarchy, they refer queries to the correct TLD name server. ICANN (Internet Corporation for Assigned Names and Numbers) coordinates the work of the root name servers. There are 13 such root servers around the world, which are made up of more than 1,600 server instances in anycast operation.

Authoritative DNS Server

Authoritative DNS servers access the domain name space of a specific zone in their database. Each zone has at least one authoritative name server that manages the zone data – the information emanating from it is considered valid.

Non-Authoritative DNS Server

Non-authoritative DNS servers pass on DNS information from external sources and are not responsible for a specific zone. Instead, they retrieve the required domain information from an authoritative DNS server when a request is made and store it in the cache.

DNS Caching Server

DNS caching servers temporarily store the information from other name servers for a certain period of time in order to answer incoming queries more quickly. The duration of this storage is determined by the authoritative name server.

DNS Forwarding Server

DNS forwarding servers are generally used in larger company networks and by internet service providers (ISPs). They receive DNS queries from clients and forward them specifically to other DNS servers in order to better distribute the network load and speed up the response.

Resolver

Resolvers are usually responsible for name resolution in a local network or on the client PC/router itself. Resolvers send requests to the DNS to resolve domain names to IP addresses.

How Does a DNS Request Work?

A DNS request is always necessary if the computer does not have the address information required to access a website in its cache and the pre-configured DNS service of the Internet service provider is also unable to resolve the name. In detail, a DNS request runs according to the following pattern:

Enter the URL of a website in the browser (e.g. www.myrasecurity.com). The operating system checks the DNS cache based on the request. If the address is not in the cache, the request is forwarded to the DNS resolver.
The DNS resolver then contacts the DNS root server.
The root server tells the resolver under which top-level domain the information for the website can be found. In the case of www.myrasecurity.com, this is the top level domain (TLD) .com
The resolver sends a request to the corresponding TLD server.
The TLD server specifies the IP address of the corresponding authoritative DNS server of the domain being searched for.
The DNS resolver asks the authoritative DNS server for the IP address of the origin server on which the website is hosted.
The name server forwards the address of the origin server to the DNS resolver.
The resolver forwards the IP address to the client's browser.
The browser now calls up the website by sending an HTTP request to the IP address.
The server contacted sends the website files to the browser so that the content is displayed.

Criticism of DNS

The concept of the DNS as the telephone directory of the web dates back to the early days of the internet, when there was no cybercrime, tracking or digital censorship. This is why encryption methods were not used for the transmission of DNS queries back then. By default, the transmission takes place unsecured in plain text. This vulnerability makes the technology a powerful tool for cybercrime, tracking or censorship.

DNS attacks

As DNS does not validate communication by default, the technology is extremely susceptible to malicious manipulation. Using DNS spoofing, cyber criminals can redirect data traffic to malicious websites in order to spread malware or steal user data.

Espionage

The DNS is largely unencrypted. There is therefore a risk that the connection between the client and DNS server can be spied on. DNS extensions such as DNSSEC provide a remedy here by being used to validate DNS queries.

Censorship

Both associations and commercial providers criticize the fact that domains can be censored via the DNS. There is also a risk that the technology could be misused for censorship via Geoblocking is misused. Authoritarian regimes use DNS blocks for political censorship, for example.

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05 – DNS Extensions and Encryption Technologies

Over the years, several standards, extensions and encrypted protocols have been developed to eliminate functional weaknesses and security gaps in name resolution. Depending on the DNS provider or DNS service, different standards and extensions are supported for name resolution.

Dyn DNS

Dyn DNS stands for "dynamic domain name system". Such services enable the user to assign a fixed host name to dynamic IP addresses. One of the areas of application is the operation of a web server despite a dynamic IP address.

Extended DNS

Extended DNS (EDNS) enables the transport of DNS data in UDP packets. Such an extension of the DNS packet format proved to be necessary in the 1990s, as the restrictions in the previous DNS packets no longer met modern requirements.

DNSSEC

DNSSEC describes a series of security extensions for the DNS that guarantee the authenticity and integrity of the data transmitted via the system. By encrypting data transmissions in the DNS, the privacy and data security of users is ensured.

DNS over HTTPS

DNS over HTTPS (DoH) is currently one of the most common solutions for DNS encryption alongside DoT. With DoH, DNS queries and responses are sent in the secure HTTPS website protocol via port 443. This means that the transmissions can no longer be distinguished from conventional website traffic, which prevents targeted blocking. Compared to conventional DNS name resolution, DoH is less performant. DoH was standardized by the IETF in 2018 as RFC 8484.

DNS over TLS

DoT is a standard proposed by the Internet Engineering Task Force (IETF) (RFC 7858) for securing DNS connections. In contrast to conventional DNS queries, DoT establishes a secure TCP connection (Transmission Control Protocol) between the client and DNS server, which is authenticated and encrypted using TLS. Technically, name resolution using DoT takes place via TCP port 853.

DNSCrypt

DNSCrypt is a protocol that is used to encrypt, authenticate and optionally anonymize communication between the DNS client and DNS resolver. Data traffic to the DNS resolver is secured using asymmetric encryption. By default, DNSCrypt uses port 443. To anonymize DNS queries, DNSCrypt can be extended with Anonymized DNS technology, which is also compatible with the other encrypted protocols.

DNS over QUIC

DNS over QUIC (DoQ) is a new protocol that is being standardized by the IETF. DoQ aims to combine the advantages of encrypted name resolution with short latency times. For high-performance data transfer, DoQ uses the new QUIC protocol, which is also used in HTTP/3 and relies on TLS 1.3 for security.

What Are the Dangers of DNS?

Due to the existing vulnerabilities, cyber criminals can abuse the domain name system as a powerful weapon. For example, changes to the DNS delegation structure can be used to redirect traffic to malicious websites. It is also possible to spy on established connections or use DNS servers as a DDoS attack tool. The most common DNS attacks include:

DNS Attacks Overview
DDoS Attack
In addition, name servers themselves are a popular target for overload attacks. A prominent example of this is the attack on Dyn's DNS infrastructure in October 2016, when several globally recognised websites such as Twitter and PayPal were unavailable for several hours.
DNS Attacks Overview
DNS Spoofing
This is a collective term for malicious DNS manipulations aimed at redirecting Internet users to a specific resource. DNS spoofing includes attacks using DNS cache poisoning, in which manipulated entries are smuggled into the DNS cache of name servers, or DNS hijacking, in which cybercriminals aim to take control of DNS settings on clints, servers and DNS infrastructure using malware or by exploiting security vulnerabilities.
DNS Attacks Overview
DNS Cache Poisoning
In cache poisoning, cyber criminals abuse the functionality of the Domain Name System (DNS) to lure internet users to fake websites without them noticing and steal their access data and other sensitive information. If attackers succeed in corrupting a name server via security vulnerabilities and injecting fake entries into the delegation structure, the manipulated entries also end up in the cache of requesting servers, routers and end devices that request the affected domain on the name server. The DNS cache is now "poisoned" and redirects users to the website specified by the attackers.
DNS Attacks Overview
DNS Hijacking
DNS hijacking describes an attack technique in which attackers manipulate DNS records to redirect queries to fraudulent websites. This can be done by compromising client PCs, routers, DNS servers or by intercepting DNS queries. Depending on the system affected, IT security distinguishes between "local hijacking", "router hijacking", "rogue DNS server attacks" and "man-in-the-middle attacks".
DNS Attacks Overview
DNS Reflection & Amplification
Cyber criminals can use IP spoofing to abuse DNS servers as a powerful tool for distributed denial-of-service attacks (DDoS). They exploit weaknesses in the DNS to increase the power of the attack many times over.
DNS Attacks Overview
DDoS Attack
In addition, name servers themselves are a popular target for overload attacks. A prominent example of this is the attack on Dyn's DNS infrastructure in October 2016, when several globally recognised websites such as Twitter and PayPal were unavailable for several hours.
DNS Attacks Overview
DNS Spoofing
This is a collective term for malicious DNS manipulations aimed at redirecting Internet users to a specific resource. DNS spoofing includes attacks using DNS cache poisoning, in which manipulated entries are smuggled into the DNS cache of name servers, or DNS hijacking, in which cybercriminals aim to take control of DNS settings on clints, servers and DNS infrastructure using malware or by exploiting security vulnerabilities.

DNS: What You Need To Know

The Domain Name System is the basis for enabling users to access websites on the Internet via their domain. The technology determines which IP address is to be used for the respective domain. As an essential service on the internet, the DNS is an attractive target for cyber criminals – especially as the technology itself does not have any extensive security functions. Communication between the client and DNS server is usually unencrypted and in plain text. This provides a large attack surface for manipulation, sabotage and espionage. This makes it all the more important for organizations with critical online business processes to rely on a secure DNS infrastructure that is protected against malicious access from outside.

Myra Secure DNS secures the name resolution of your company domain against attacks and ensures the accessibility of your systems and services. Secure DNS relies on high-performance anycast routing and is operated on specially hardened server instances and secured by the same BSI-certified protection technology used by the German government, among others, to defend its domains against cyber attacks.

As a Security-as-a-Service solution, Secure DNS from Myra is implemented and ready for use in a short space of time. No additional software or hardware is required for operation. Myra is a long-standing service partner of various federal, state and local authorities, well-known banks and insurance companies as well as operators of critical infrastructures (KRITIS).