LuminousMoth APT: Sweeping attacks for the chosen few

[harlan4096]

APT actors are known for the frequently targeted nature of their attacks. Typically, they will handpick a set of targets that in turn are handled with almost surgical precision, with infection vectors, malicious implants and payloads being tailored to the victims’ identities or environment. It’s not often we observe a large-scale attack conducted by actors fitting this profile, usually due to such attacks being noisy, and thus putting the underlying operation at risk of being compromised by security products or researchers.

We recently came across unusual APT activity that exhibits the latter trait – it was detected in high volumes, albeit most likely aimed at a few targets of interest. This large-scale and highly active campaign was observed in South East Asia and dates back to at least October 2020, with the most recent attacks seen around the time of writing. Most of the early sightings were in Myanmar, but it now appears the attackers are much more active in the Philippines, where there are more than 10 times as many known targets.

Further analysis revealed that the underlying actor, which we dubbed LuminousMoth, shows an affinity to the HoneyMyte group, otherwise known as Mustang Panda. This is evident in both network infrastructure connections, and the usage of similar TTPs to deploy the Cobalt Strike Beacon as a payload. In fact, our colleagues at ESET and Avast recently assessed that HoneyMyte was active in the same region. The proximity in time and common occurrence in Myanmar of both campaigns could suggest that various TTPs of HoneyMyte may have been borrowed for the activity of LuminousMoth.

Most notably though, we observed the capability of the culprit to spread to other hosts through the use of USB drives. In some cases, this was followed by deployment of a signed, but fake version of the popular application Zoom, which was in fact malware enabling the attackers to exfiltrate files from the compromised systems. The sheer volume of the attacks raises the question of whether this is caused by a rapid replication through removable devices or by an unknown infection vector, such as a watering hole or a supply chain attack.

In this publication we aim to profile LuminousMoth as a separate entity, outlining the infection chain and unique toolset it leverages, the scale and targeting in its campaigns as well as its connections to HoneyMyte through common TTPs and shared resources.

What were the origins of the infections?

We identified two infection vectors used by LuminousMoth: the first one provides the attackers with initial access to a system. It consists of sending a spear-phishing email to the victim containing a Dropbox download link. The link leads to a RAR archive that masquerades as a Word document by setting the “file_subpath” parameter to point to a filename with a .DOCX extension.

hxxps://www.dropbox[.]com/s/esh1ywo9irbexvd/COVID-19%20Case%2012-11-
2020.rar?dl=0&file_subpath=%2FCOVID-19+Case+12-11-2020%2FCOVID-19+Case+12-11-2020(2).docx12hxxps://www.dropbox[.]com/s/esh1ywo9irbexvd/COVID-19%20Case%2012-11-2020.rar?dl=0&file_subpath=%2FCOVID-19+Case+12-11-2020%2FCOVID-19+Case+12-11-2020(2).docx

The archive contains two malicious DLL libraries as well as two legitimate executables that sideload the DLL files. We found multiple archives like this with file names of government entities in Myanmar, for example “COVID-19 Case 12-11-2020(MOTC).rar” or “DACU Projects.r01” (MOTC is Myanmar’s Ministry of Transport and Communications, and DACU refers to the Development Assistance Coordination Unit of the Foreign Economic Relations Department (FERD) in Myanmar).

The second infection vector comes into play after the first one has successfully finished, whereby the malware tries to spread by infecting removable USB drives. This is made possible through the use of two components: the first is a malicious library called “version.dll” that gets sideloaded by “igfxem.exe”, a Microsoft Silverlight executable originally named “sllauncher.exe”. The second is “wwlib.dll”, another malicious library sideloaded by the legitimate binary of “winword.exe”. The purpose of “version.dll” is to spread to removable devices, while the purpose of “wwlib.dll” is to download a Cobalt Strike beacon.

The first malicious library “version.dll” has three execution branches, chosen depending on the provided arguments, which are: “assist”, “system” or no argument. If the provided argument is “assist”, the malware creates an event called “nfvlqfnlqwnlf” to avoid multiple executions and runs “winword.exe” in order to sideload the next stage (“wwlib.dll”). Afterwards, it modifies the registry by adding an “Opera Browser Assistant” entry as a run key, thus achieving persistence and executing the malware with the “assist” parameter upon system startup.
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