# DNS
Domain Name Service (DNS) is used by millions of people daily. Because of this, many organizations have less stringent policies in place to protect against DNS-based threats than they have to protect

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03-17-2023, 04:22 PM
Domain Name Service (DNS) is used by millions of people daily. Because of this, many organizations have less stringent policies in place to protect against DNS-based threats than they have to protect against other types of exploits. Attackers have recognized this and commonly encapsulate different network protocols within DNS to evade security devices. DNS is now used by many types of malware. Some varieties of malware use DNS to communicate with command-and-control (CnC) servers and to exfiltrate data in traffic disguised as normal DNS queries. Various types of encoding, such as Base64, 8-bit binary, and Hex can be used to camouflage the data and evade basic data loss prevention (DLP) measures.
For example, malware could encode stolen data as the subdomain portion of a DNS lookup for a domain where the nameserver is under control of an attacker. A DNS lookup for ‘long-string-of-exfiltrated-data.example.com’ would be forwarded to the nameserver of example.com, which would record ‘long-string-of-exfiltrated-data’ and reply back to the malware with a coded response. This use of the DNS subdomain is shown in the figure. The threat actor collects this encoded data, decodes and combines it, and now has access to an entire data file, such as a username/password database.
It is likely that the subdomain part of such requests would be much longer than usual requests. Cyber analysts can use the distribution of the lengths of subdomains within DNS requests to construct a mathematical model that describes normality. They can then use this to compare their observations and identify an abuse of the DNS query process. For example, it would not be normal to see a host on your network sending a query to aW4gcGxhY2UgdG8gcHJvdGVjdC.example.com.
DNS queries for randomly generated domain names, or extremely long random-appearing subdomains, should be considered suspicious, especially if their occurrence spikes dramatically on the network. DNS proxy logs can be analyzed to detect these conditions.

> Quote:"Potential is only the expression of possibility, something that can be accesed accurately only in retrospect."

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