Bitdefender security researchers discovered a new malware strain spiking in their telemetry. The malware, which Bitdefender named MosaicLoader, is a downloader that can deliver any payload to the infected system. During their investigation, Bitdefender found that MosaicLoader threat actors used the following tactics to hinder researchers' malware analysis efforts and to increase their attacks' rate of success:

  • Mimicking file information that is similar to legitimate software
  • Code obfuscation with small chunks and shuffled execution order
  • Payload delivery mechanism infecting the victim with several malware strains

What caught the attention of researchers were processes that add local exclusions in Windows Defender for specific file names that all reside in the same folder. Bitdefender named it MosaicLoader because of the intricate internal structure that aims to confuse malware analysts and prevent reverse-engineering. MosaicLoader is seemingly delivered through paid ads in search results designed to lure users looking for cracked software to infect their devices. Once planted on the system, the malware creates a complex chain of processes and tries to download a variety of threats, from single cookie stealers to cryptocurrency miners or more complex ones, such as the Glupteba Backdoor.

Researchers at Fortinet noticed similar processes that used the same C2 as MosaicLoader investigated by Bitdefender. In that case, attackers asked them to remove detection on the file net-helper.exe. The trick used by the malicious actors was to create seemingly executable files including manifest information such as company name and description that was related to the files name. The attackers stuck to this approach with the newer droppers, mimicking executable files that belong to legitimate software. While the execution flow of the malware is somewhat similar to Warzone RAT, the C2 servers and the delivered payloads do not seem related to the actors behind Warzone. 

Erkang Zheng, Founder and CEO at JupiterOne, says, "The line between personal and business devices will continue to blur. It is a reality we have to acknowledge and accept. Users will always find ways to get around the "gates" to make things easier for themselves. Organizations should absolutely have a clear endpoint device management / BYOD policy and the corresponding awareness training. In addition to the policy and training, consider the following technical control in two implementation steps: 

1) Define what critical access means (e.g. access to production or environments/systems with confidential data)

2) Implement device trust so that users can only use certified devices meeting certain corporate security for critical access

"This provides a balanced approach to protect the "crown jewels" while allowing certain flexibility to employee's device usage."

"Productivity and gaming software have been a target for many years disguised as a fun or helpful application. Unfortunately, lurking in the background of those apps is a malicious attacker looking to gain remote access or harvest off credentials used by the unsuspecting victim," explains Joseph Carson, chief security scientist and Advisory CISO at ThycoticCentrify. "This is not really a new technique, however, it is becoming more successful now that employees are working remotely on unprotected networks where they are continuously switching between personal and corporate devices.  In fact, our recent research found that employees are willing to take a risk because they don’t believe they are a target of cybercriminals and that they have an IT security team that is protecting them."

Carson adds, "The average employee isn’t proficient in cyber hygiene and best practices, making them easy targets for cybercriminals looking to access an organization's networks quickly and easily. By ensuring that employees at every level are given sufficient training can be a major step forward in helping decrease the success rate of an attack. By normalizing training within the workplace culture, organizations can help maintain attentiveness for the long term."