Introduction To Malware Infrastructure Analysis With Passive DNS

We recently became aware of an awesome DNS Analysis tool called Validin which can be used to analyse malicious domains and show related infrastructure using DNS records.

This has been super useful as existing infrastructure analysis tools are primarily focused on analysis and pivoting from IPs, which functions very differently to pivoting from domains.

The primary concept of DNS pivots is simple, use the DNS history and domain names to identify patterns and related indicators which threat actors have re-used when deploying infrastructure.

Since we're having a lot of fun with the tool and the techniques, we wanted to share some cool and useful examples that we have encountered so far.

You can follow along with the free community version available here.

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Practical Use Cases

Identifying the history of a domain (Current and Previous IP's)
Finding lookalike domains with similar names
Identifying domains that resolve to the same IP
Identifying domains with a similar parent domain (.duckdns.org, .ddns etc)

LokiBot - Identifying IP History

As an initial example using Validin, we can take this domain which was reported as Lokibot on ThreatFox.

By searching for this domain sempersim[.]su , we can obtain a full history of IP infrastructure related to this domain.

(A link to this search can be found here and followed with a free account)

There are a large number of IPs associated with this domain. The first is from 2022 and has constantly changed since then.

This is an indicator that the actor is regularly changing up their infrastructure, possibly in response to intel sharing or takedowns.

This can be better visualized in the timeline feature demonstrated below. Many of the IPs are short-lived, and some have lasted longer than others.

In the initial search on our sempersim[.]su domain, the most recently added result was an IP address of 104.237.252[.]28.

We can do a pivot on this IP address and view the history of related domains, this allows us to identify additional domains which have resolved to the same server as sempersim[.]su

By searching or clicking on 104.237.252[.]28, we can pivot on this IP and see if there are any recent domains pointing to the same location.

In this case, there are 6 domains that have been pointing at this address in the 2 weeks prior to this analysis.

Four of these results seem to be impersonating Icloud services (Using L instead of I).

The resulting domains can be investigated and validated with other tooling, here is one such example of the first related domain lcloud.com[.]de in Virustotal.

The remaining results are highly suspicious and are likely related to the same actor as the initial sempersim[.]su domain.

Identifying LookAlike Domains

The previous analysis pivoted from sempersim[.]su to identify a new domain of lcloud.com[.]de (L instead of I).

This new indicator is highly suspicious as it appears to be impersonating an Apple icloud service.

If an actor is utilising one fake ICloud domain, they potentially have more using the same technique. We can validate this theory using the lookalike domain feature on the lcloud.com[.]de domain.

This search returns 1033 total results for domains with the same mispelling, but for the purposes of demonstration, we will use the first new result of lcloud.com[.]se.

Pivoting on this new .se domain reveals a history of 15 IP addresses ranging from 2019 to 2023.

The most recent (based on first seen) of these ip addresses is 194.295.220[.]41, initial analysis of this IP with Virustotal reveals 9 related detections.

Review of the communicating files for this IP reveals multiple files related to the "Bagle Worm"

We are not particularly familiar with Bagle, but at first glance it seems wildly different to the initial indicator which was based on LokiBot.

This could be an indicator that the actors behind Lokibot and Bagle are sharing the same infrastructure, or could be an indicator that they are the same actor.

Exact attribution is beyond the scope of this post, but it's an interesting note that the two are potentially sharing infrastructure or at least leveraging extremely similar domains.

Returning to our pivot on sempersim[.]su, we identified an IP address of 104.237.252[.]28 which is also related to www.icloud-find-online[.]me.

By pivoting to this new domain www.icloud-find-online[.]me, we can see the full history of IPs related to the domain.

By observing the ASN numbers and the presence of the "cloud" symbol next to the ASN, we can see that the actor behind this domain began to use CloudFlare as of 2024-03-19

This isn't particularly useful to me, but seeing it visualized like this is cool. More experienced intel analysts may have plenty of use for this information.

Here we have another highly suspicious domain name marxrwo9090.duckdns[.]org which was reported as Xworm on ThreatFox.

By analysing this domain, we can see that only a single IP of 194.147.140[.]138 has been associated.

By pivoting on this IP address, we can identify a number of suspicious .duckdns.org domains pointing to the same location.

One of these results specifically calls out Xworm as febxworm39090.duckdns[.]org

There are 25 domains associated with the address 194.147.140[.]138, and we can again visualise these with the timeline feature.

Here, we can see the actor has regularly updated their domains and has primarily relied on dynamic DNS services such as ddns and duckdns.

Xworm - Pivoting Across CIDR Ranges

In the previous section, we identified that the actor was regularly using dynamic DNS services to mask the IP at 194.147.140[.]138

If we consider that the same actor may be using the same ASN or hosting provider to host similar infrastructure, we can craft a query to identify additional related domains.

Consider that the initial IP 194.147.140[.]138 belongs to an AS with a CIDR range 194.147.140.0/24

(This section is similar to that published by Gi7w0rm on his DDGroup Analysis, so be sure to check that out too)

We can expand the search to query this range, which reveals 1468 domains with IP addresses resolving to the ASN. Many of these domains also rely on dynamic dns services such as ddns and duckdns.

A total of 464 domains are leveraging duckdns and resolving to the same ASN. Many of these have highly suspicious names and are very recent.

The first of such results is elastolut.duckdns[.]org , which has 11 detections on Virustotal and multiple malicious (and very recent) communicating files.