Pierluigi Paganini
July 19, 2022
Researchers from ESET discovered a previously undetected macOS backdoor, tracked as CloudMensis, that targets macOS systems and exclusively uses public cloud storage services as C2.
The malware was designed to spy on the target systems, exfiltrate documents, acquire keystrokes, and screen captures.
CloudMensis was developed in Objective-C, the samples analyzed by ESET are compiled for both Intel and Apple architectures.
Experts have yet to determine how the victims are initially compromised by this spyware.
“However, we understand that when code execution and administrative privileges are gained, what follows is a two-stage process, where the first stage downloads and executes the more featureful second stage.” reads the report published by ESET. “Interestingly, this first-stage malware retrieves its next stage from a cloud storage provider. It doesn’t use a publicly accessible link; it includes an access token to download the MyExecute file from the drive. In the sample we analyzed, pCloud was used to store and deliver the second stage.
Experts pointed out that the malware was employed in highly targeted operations because of its very limited distribution.
The attack chain detailed by ESET is composed of two phases, in the first stage, the malware retrieves its next stage from a cloud storage provider. The malicious code includes an access token to download the MyExecute file from the drive. In the sample analyzed by ESET, the malicious code was using pCloud provider as a storage for the second stage malware that implements the spyware capabilities.
The analysis of the artifacts in both components suggests they are called “execute” and “Client” by the authors of the threat.
“The first-stage malware downloads and installs the second-stage malware as a system-wide daemon.” continues the post. “At this stage, the attackers must already have administrative privileges because both directories can only be modified by the root user.”
The “execute” component includes a method called removeRegistration that cleans up after a successful Safari sandbox escape exploit. The exploit chain uses four flaws that were disclosed in 2017, a circumstance that suggests that CloudMensis may has been active since at least 2017 evading the detection.
The malware is also able to bypass the Transparency, Consent, and Control (TCC) security feature, which prevents that any app could access files in Documents, Downloads, Desktop, iCloud Drive, and network volumes without obtaining the explicit user consent.
Experts noticed that the malware communicates with C2 infrastructure using authentication tokens to multiple cloud service providers (Dropbox, pCloud, and Yandex Disk) that were stored into the CloudMensis configuration.
The backdoor supports 39 commands, including:
“From what we have seen, operators of this malware family deploy CloudMensis to specific targets that are of interest to them. Usage of vulnerabilities to work around macOS mitigations shows that the malware operators are actively trying to maximize the success of their spying operations. At the same time, no undisclosed vulnerabilities (zero-days) were found to be used by this group during our research.” concludes the report. “Thus, running an up-to-date Mac is recommended to avoid, at least, the mitigation bypasses.”
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(SecurityAffairs – hacking, CloudMensis)
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