A newly identified remote access Trojan (RAT) that has been written entirely in Python is being used in highly targeted attacks, Cisco Talos researchers say.
Dubbed CannibalRAT, the malware lacks sophistication but exhibits signs of code cannibalization. At least two variants (versions 3.0 and 4.0) have been already used in attacks, both with the usual RAT capabilities, but the latter lacking features to fit a campaign targeting users of a Brazilian public sector management school.
The malicious activity associated with the RAT has increased after the second variant (4.0) emerged on February 5, 2018 (the first variant was spotted on Jan. 8). The newer iteration also uses obfuscation to avoid detection: it was packed with UPX and has a function to generate random strings in memory.
Both variants use base16 encoding scheme to obfuscate command and control (C&C) hostnames and data exchanged with the server. Also, both use the “CurrentVersionRun” registry key for persistence, along with the service name “Java_Update“, Cisco reveals.
Once executed on the infected machine, version 4.0 creates a PDF file with HTML code embedded, designed to load an image hosted at imgur.com, and launches Chrome to open the PDF.
Both versions connect to the same C&C infrastructure, but the older one uses standard web requests, while the newer version uses a REST-based API. The latter method would send username, hostname, and capability related information to the server as part of the initial request.
The credential-stealer modules are copied from the Radium-Keylogger’s source code (available on Github), while the VM detection function was copied from a different Github repository.
This, the researchers say, shows the large amount of code that adversaries share among them, which makes attribution even more difficult.
The malware’s modules have self-explanatory names: runcmd, persistence, download, upload, screenshot, miner, DDoS, driverfind, unzip, ehidden, credentials, file, zip, python, update, and vm. All are present in version 3.0, while version 4.0 lacks the distributed denial of service, miner, Python and update modules, as well as the ability to steal credentials from Firefox (it only works with Chrome).
The latest version also drops the module approach and includes all code in the main script. Furthermore, it includes four possible C&C hostnames (version 3.0 only had two), and randomly chooses one upon execution.
The attackers use the fast flux technique to hide the infrastructure and change name servers with high frequency (120 seconds), but the end points tend to be the same, belonging to a telecom provider in Brazil, the researchers say.
One of the domains associated with the campaign (the malware was hosted on it) is inesapconcurso.webredirect.org, apparently specifically created for these attacks. The actor used social engineering for the name as well: inesapconcurso is the aggregation of inesap and concurso, representing the school name and the Portuguese word for “competition”.
“While the objective of this campaign is unclear, the adversaries went through some work in order to keep their RAT as unnoticed as possible. Both the campaign target and the command-and-control visibility show this campaign is active in Brazil, which our DNS data confirms, reflecting the highly targeted approach of this campaign,” Cisco concludes.
