Zone Transfer Attacks: A Practical Guide to Detection and Prevention
A zone transfer attack is a type of cyber attack that targets Domain Name System (DNS) servers. It involves an attacker requesting and receiving a copy of the entire DNS database, also known as a zone file, from a DNS server. This database contains a list of all the domain names and corresponding IP addresses registered on the server, as well as other important information such as mail server addresses and resource records.
There are two types of zone transfer attacks: full zone transfers (AXFR) and incremental zone transfers (IXFR | partial zone transfer). A full zone transfer involves the attacker requesting and receiving a complete copy of the DNS database from the server. An incremental zone transfer, on the other hand, involves the attacker requesting and receiving only the changes made to the database since the last time it was updated.
AXFR Zone Transfer (Full Zone Transfer):
AXFR (Full Zone Transfer) is a type of DNS zone transfer that replicates the entire DNS zone from the master server to the slave server. This is done when the slave server is being set up or when the master server has been updated with new DNS resource records.
IXFR Zone Transfer (Partial Zone Transfer):
IXFR (Partial Zone Transfer) is a type of DNS zone transfer that replicates only the changes made to the DNS zone on the master server to the slave server. This is done when the master server has been updated with new DNS resource records and the slave server needs to be updated with the changes.
Zone transfers are typically used to synchronize DNS information between servers, such as when a new server is added to a network or when an existing server is updated. However, they can also be exploited by attackers in a process known as a zone transfer attack.
Why Zone Transfer Attacks Occur:
An attacker can conduct a zone transfer attack by finding a DNS server that is vulnerable to such attacks and requesting a copy of the zone file from the server. If the server is configured to allow zone transfers and the attacker is able to bypass any security measures in place, it will respond by sending the complete zone file or a partial version of it.
Once an attacker has a copy of the zone file, they can use it to launch various types of attacks, such as phishing scams, spamming, and domain hijacking. They can also use the information in the file to conduct further reconnaissance on the target organization, gathering information about its infrastructure, network, and employees.
How to Detect and Exploit Zone Transfer Attacks:
To detect and exploit a zone transfer attack using the command line, an attacker would first need to find a DNS server that is vulnerable to such attacks. This could involve using tools and techniques to scan for DNS servers on the internet and identify those that are not properly secured or have known vulnerabilities.
Once the attacker has identified a target DNS server, they can use the “dig” command to request a copy of the zone file from the server. The command might look something like this:
# dig @[server_IP_address] [domain_name] axfrIf the DNS server is configured to allow zone transfers and the attacker is able to bypass any security measures in place, it will respond by sending the complete zone file or a partial version of it. The attacker can then save the file to their local machine and use it to launch further attacks or gather information about the target organization.
Imagine an attacker trying to gather information about a company’s network and infrastructure. They start by finding the company’s DNS server and attempting a zone transfer attack. The attacker sends a request to the DNS server for a copy of the zone file, and the server responds by sending the entire database.
The attacker now has a complete list of all the domain names and corresponding IP addresses registered on the server, as well as other important information such as mail server addresses and resource records. They can use this information to launch various types of attacks, such as phishing scams, spamming, and domain hijacking. They can also use the information to conduct further reconnaissance on the target organization, gathering even more information about its infrastructure and network.
Perform Zone Transfer Attack on ZoneTransfer.me:
I am performing a Zone Transfer Attack on ZoneTransfer.me which always has zone transfer enabled.
Step:1 Resolve the ns Record of the domain “ZoneTransfer.me”. Here I used the dig tool you can also use nslookup and host command.
# dig ns ZoneTransfer.me
# nslookup -type=ns zonetransfer.me
# host -t ns zonetransfer.me
Step:2 Identify the primary DNS server by resolving soa record.
# dig soa ZoneTransfer.me
# nslookup -type=soa example.com 8.8.8.8
# host -t soa example.com 8.8.8.8
Step:3 Exploit Zone Transfer Attack using “nsztm1.digi.ninja” Name Server
# dig axfr @nsztm1.digi.ninja zonetransfer.me
# nslookup -type=axfr zonetransfer.me nsztm1.digi.ninja
# host -t axfr zonetransfer.me nsztm1.digi.ninja
Here is the response we get the all records of the domain “zonetransfer.me” from the primary Name Server. :)
What is a DNS Zone and DNS Zone Files:
A DNS (Domain Name System) zone is a portion of the DNS namespace that is managed by a specific administrator or organization. It includes a set of DNS resource records that provide information about a domain and its subdomains.
A DNS zone file is a text file that contains a list of all the domain names and corresponding IP addresses registered on a DNS server, as well as other important information such as mail server addresses and resource records. The format of a DNS zone file is based on the Resource Record (RR) format specified in the Domain Name System (DNS) protocol.
DNS Zone File Format:
DNS zone files use a specific format to store the DNS resource records. The basic structure of a DNS zone file is as follows:
[domain_name] [TTL] [class] [type] [data]Here is a breakdown of the different parts of this structure:
[domain_name]: This is the domain name that the resource record is associated with.
[TTL]: The Time To Live (TTL) value specifies how long the resource record is valid before it needs to be refreshed.
[class]: The class value specifies the type of network the resource record is associated with. The most common value is “IN” for the Internet.
[type]: The type value specifies the type of resource record being defined. Some common types include “A” for an IP address, “MX” for a mail server, and “CNAME” for a domain name alias.
[data]: The data value contains the actual data associated with the resource record. For example, if the type is “A”, the data value would be an IP address. If the type is “MX”, the data value would be the mail server’s domain name.
Each resource record has a specific type and is written in a specific format. Here is an example of a DNS zone file with multiple resource records:
example.com. 3600 IN A 192.0.2.1
mail.example.com. 3600 IN A 192.0.2.2
www.example.com. 3600 IN CNAME example.com.
mail.example.com. 3600 IN MX 10 mail.example.com.In this example, the first resource record associates the domain “example.com” with the IP address “192.0.2.1”. The second resource record associates the subdomain “mail.example.com” with the IP address “192.0.2.2”. The third resource record creates an alias for “www.example.com" that points to “example.com”, and the fourth resource record specifies that the mail server for “example.com” is “mail.example.com”.
Zone files are simple text files with DNS records. A zone file will contain the whole information for a domain:
SOA record, which indicates the start of authority.
A record for IPv4 addresses.
AAAA record for IPv6 addresses.
CNAME record for canonical records that indicate the canonical domain.
MX record for the receiving email servers for the domain.
TXT record for various verification methods
SRV record for services.
PTR record for a reverse DNS lookup.
And more.
What is a DNS Master Zone:
A DNS master zone is a DNS zone that is configured as the primary source of information for a specific DNS namespace. It is the authoritative source of information for a domain and its subdomains.
The DNS master zone is usually managed by the administrator of the domain and is used to store the DNS resource records for the domain. Any changes to the DNS resource records in the master zone will be replicated to the other DNS servers that are configured as slaves for the zone.
Why Is DNS Zone Transfer Needed:
DNS zone transfer is needed to ensure that all DNS servers have the same information about a domain and its subdomains. This is important because DNS servers are used to resolve domain names to IP addresses, and if the DNS servers have different information about a domain, it can lead to confusion and errors.
By replicating the DNS resource records from the master server to the slave servers, DNS zone transfer ensures that all DNS servers have the same information and can serve DNS queries accurately. This helps to maintain the integrity of the DNS system and ensures that domain names can be resolved correctly.
Recommendations:
To prevent this type of attack, there are several measures that organizations can take:
Implement security measures at the DNS server level: This can include restricting access to the server, configuring firewalls to block unauthorized access, and implementing authentication and encryption protocols to secure data transmissions.
Limit access to trusted IP addresses: Configure the DNS server to only allow zone transfers from trusted IP addresses, such as those belonging to the organization’s own network.
Keep software and hardware up to date: It is also important to keep the DNS software and server hardware up to date with the latest security patches and updates. This will help to protect against vulnerabilities that could be exploited by attackers.
Monitor for suspicious activity: Use monitoring tools to detect and alert on unusual or suspicious activity on the DNS server, such as unauthorized access attempts or a large volume of requests for zone transfers.
By following these recommendations, organizations can significantly reduce the risk of a successful zone transfer attack and protect their sensitive information from being compromised.
In conclusion, zone transfer attacks are a serious threat to organizations, as they can compromise sensitive information and lead to further cyber attacks. Implementing security measures at the DNS server level, limiting access to trusted IP addresses, and regularly updating software and hardware can help to prevent these attacks and protect against the potential damage they can cause.
