Security Experts:

Modular Felismus RAT Emerges

A newly discovered piece of malware features a modular design and has been used in highly targeted campaigns, Forcepoint security researchers reveal.

Dubbed Felismus, the malware is a well-written Remote Access Trojan (RAT) believed to have been created by professional cybercriminals. The threat packs numerous anti-analysis capabilities (including advanced encryption of network communication) and shows good 'operational hygiene' relating to the re-use of email addresses and other traceable artefacts, Forcepoint says.

The first available samples feature filenames mimicking that of Adobe's Content Management System (AdobeCMS.exe) and emerged several weeks ago, but the malware’s attacks can be dated six months before. The attackers behind the malware and their targets remain opaque for the time being, but the RAT’s libraries appear to be actively exploited and the spotted attacks are believed to be part of a larger campaign.

The threat is capable of self-updating, while also being able to identify and evade a large number of anti-virus products, most of which are well-known brands. The malware packs capabilities typical of RATs, such as file upload, file download, file execution, and shell (cmd.exe) command execution. The malware can also create text files on the local machine.

At the time of publishing, 31 of 61 anti-virus products on VirusTotal detected the threat based on the hash provided by ForcePoint.

The security researchers note that the malware’s command and control (C&C) infrastructure is active and appears to be maintained, while also revealing that the RAT uses at least three separate encryption methods for its traffic, depending on the type of message.

A series of domains associated with the threat were found to return a fake page from 2013, and to feature falsified details, such as invalid Hong Kong-based telephone numbers and inexistent street addresses. The email addresses used to register the domains haven’t been used anywhere else online, which confirms the degree of professionalism and good 'operational hygiene' these cybercriminals are using.

“The malware analysed appears to be both modular and well-written, strongly suggesting that skilled attackers are responsible, while its apparent scarcity in the wild implies that it is likely highly targeted. On top of this, the good 'operational hygiene' relating to the re-use of email addresses and other similarly traceable artefacts suggests coordinated, professional actors and, at the time of writing, there is little to link it with any known campaigns (APT-linked or otherwise),” Forcepoint says.

The security researchers say that, while the malware is well-written, the use of a folder name 'datas' and a typo in the function name 'GetCurrtenUserName' suggest that English might not be the authors’ first language. They also discovered that the available malware samples appear to have been compiled using a December 2014 version of the open-source TDM-GCC compiler suite.

The analyzed sample performed a small number of functions and generated only several unique log file entries, which could be indicative of the fact that either the campaign is currently dormant or the malware behaves differently depending on the infected machine. The researchers also noticed that a C&C IP address appeared to selectively block one of the security firm’s exit IPs during research.

“If the other modules and capabilities associated with the malware remain a matter of speculation, so too do the intended target(s). Of the five domains hosted on the C&C IP address identified within this post, three - cosecman[]com, nasomember[]com, and unmailhome[]com - have potential associations with the financial services sector; however, under this theory the naming of the remaining two domains - maibars[]com and mastalib[]com - remain unexplained,” Forcepoint concludes.

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