We continue monitoring the campaigns using information stealer BazarLoader (detected by Trend Micro as TrojanSpy.Win64.BAZARLOADER, TrojanSpy.Win64.BAZARLOADER, and Backdoor.Win64.BAZARLOADER). While InfoSec forums have noted the spike in detections during the third quarter, we noticed two new arrival mechanisms included in the existing roster of delivery techniques that malicious actors abused for data theft and ransomware.
One of the methods involves the use of compromised software installers as malicious actors bundle BazarLoader with legitimate programs. The second method involves the use of an ISO file with a Windows link (LNK) and dynamic link library (DLL) payload. We observed the Americas as the region with the highest counts of BazarLoader. For more technical analysis and insights into BazarLoader’s infection chains and campaigns, read our technical brief here.
Arrival via compromised installers
During one of our monitoring routines, we found compromised versions of VLC and TeamViewer packages bundled with BazarLoader. While the initial delivery mechanism has yet to be identified, it’s possible that the use of these packages are part of a wider social engineering technique to deceive users into downloading and implementing the compromised installers.
As the installers load, it drops and executes a BazarLoader executable. This is also one of the notable differences from recent BazarLoader arrival mechanisms wherein the malicious actors appeared to favour dynamic link libraries (DLL).
Using Trend Micro Vision One, we tracked the installer creating a process, “vlc-3.0.16-win3..2.tmp,” after executing ste.exe, which copies the latter executable to the disk and executes it. It then connects with the command and control (C&C) server and injects a copy of itself into a new suspended MS Edge process.
Arrival via ISO file
Meanwhile, we also found a delivery mechanism abusing ISO files, wherein DLL and LNK files contained inside execute the BazarLoader DLL in it. The LNK file uses a folder icon to deceive the user into double clicking the icon, enabling the file to run the enclosed BazarLoader DLL file.
It then calls the export function “EnterDLL,” a function that BazarLoader has used recently. Rundll32.exe loads the malicious DLL and communicates with the C&C server, then proceeds to spawn a suspended MS Edge process to inject itself into it.
The number of arrival mechanism variations used in BazarLoader campaigns continue to increase as threat actors diversify their attack patterns to evade detection. However, both techniques are noteworthy and still work despite their lack of novelty due to singular detection technologies’ limitations. For instance, while the use of compromised installers has been observed with other malware, the large file size can still challenge detection solutions — such as sandboxes — which may implement file size limits. On the other hand, LNK files serving as shortcuts will also likely be obfuscated for the additional layers created between the shortcut and the malicious files itself.
In addition, the deployment of BazarLoader malware for initial access is a known technique for modern ransomware such as Conti and Ryuk as service affiliates. Aside from these known ransomware families including more tools for entry into their arsenal, other malware groups and ransomware operators may pick up on the additional means, if they have not already done so.
BazarLoader is an example of a versatile malware delivery mechanism that will likely find more ways to adapt to deceive more users. For details on all the other measures that BazarLoader uses to get into systems, read our technical brief here.
Here are some best practices to defend against this threat:
- Enable security solutions that allow for visibility in tracking processes of files, allowing security teams to detect malicious outgoing and incoming network communication and traffic.
- Download installers and updates only from their respective official websites and platforms.
Trend Micro solutions
BazarLoader will continue to evolve as an information stealer malware on its own, an initial access malware-as-a-service (MaaS) for other malware operators, and as an enabler for secondary payload delivery for even more disruptive attacks like modern ransomware. Security teams must make monitoring and tracking for known threats more visible based on known data and use multilayered solutions capable of pattern recognition and behaviour monitoring for unknown threats.
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Indicators of Compromise (IOCs)
Visit this page to view the full list of IOCs.