Not a dream job: Hunting for malicious job offers from an APT

Tldr: A recent Mandiant’s blog described a series of targeted attacks over Whatsapp by an APT cluster named UNC4034. We found several additional cases in VirusTotal which we believe with high confidence are related to the same activity set.

According to the original publication, this activity is most likely related to North Korean actor and could be an extension of Operation “Dream Job”, leveraging targeted distribution of malicious ISO files. Based on Mandiant’s research, in the first stage the attacker sends a job offer at Amazon to the victim by email, followed by a WhatsApp web message where the attacker shares a malicious ISO file, pretending to be part of the selection process.

The original publication provides 2 hashes of ISO files named amazon_test.iso and amazon_assessment.isorespectively. Unfortunately, only the first one was found in VirusTotal:

8cc60b628bded497b11dbc04facc7b5d7160294cbe521764df1a9ccb219bba6b
e03da0530a961a784fbba93154e9258776160e1394555d0752ac787f0182d3c0

Hunting for more samples

We started by trying to find the ISO we were missing in VirusTotal by searching for files with the same name:

name:”amazon_assessment.iso”

The search results provided us with one sample (dc20873b80f5cd3cf221ad5738f411323198fb83a608a8232504fd2567b14031). In Mandiant’s publication both samples share the same configuration which can be found in an embedded Readme.txt file. The new sample seems to be the new variant with a different configuration, also in a Readme.txt file, as shown below:

New sample’s Readme.txt content

Both ISO files contain two files inside them – a Windows executable (apparently a poisoned version of Putty) and Readme.txt. We decided to search for all the ISO samples bundling only two specific files – Readme.txt and an *.exe file. Additionally, we filtered out all samples over 10Mb or submitted to VirusTotal before 2020. We obtained the following 6 samples, including the ones already discussed:

Volume name (included in the ISO file metadata) can also be used as a pivoting point, as an alternative to the previous query, to find more samples in VirusTotal by clicking on them:

Example of ISO metadata

We could use the following query based on metadata that also filters out results based on the previous criteria:

metadata:ASSESSMENT tag:isoimage size:10mb-

Not only PuTTY 

Although we didn’t deeply analyze the found samples, we spotted two more remote client tools in addition to Putty inside the ISO files – a weaponized versions of TightVNC Viewer and KiTTY (PuTTY’s fork). 

Interestingly, a couple of samples reveal forgotten pdb paths that could point to the attacker’s environment:

PDB path reveals “Work” folder

A TightVNC sample also included the following pdb path:

Also, in some cases attackers reused the same ISO details for different campaigns. For instance, they didn’t change the volume name (Amazon related) with the ISO name they distributed (SA_Assessment or IT_Assessment).

Infrastructure

We extracted all the IP addresses from the Readme.txt files, as well as the contacted hosts during sandbox execution.

Please note these IPs are subject to double checking before adding them to any blocking list. By checking the VirusTotal IP report  for any of them, you can find in the “Relations” tab  the “Files Referring” section to obtain which files hardcode the IP address, and “Communicating Files” to get which files contacted the IP during sandbox execution:

Files with hardcoded 143.244.186[.]68

Conclusions

As a result of this quick research we identified additional samples that seem to be part of the same campaign described by Mandiant, in this case expanding the scheme behind its distribution to, apparently, Dell and IBM in addition to Amazon. Submissions of the identified samples are observed between June and September 2022. 

In this post we described some ideas we used to identify these samples, but we encourage security researchers to both monitor additional activity and to dig into the newly found samples found to reveal further stage payloads. We created a VirusTotal Collection including the indicators associated with this malicious activity. As always, we are happy to hear any additional ideas to hunt for malicious campaigns.

原文始发于微信公众号 VirusTotal Blog：Not a dream job: Hunting for malicious job offers from an APT