Cybersecurity researchers from ExaTrack recently discovered a previously undetected malware family, dubbed Mélofée, targeting Linux servers.
The researchers linked with high-confidence this malware to China-linked APT groups, in particular the Winnti group.
The Mélofée malware includes a kernel-mode rootkit that’s based on an open-source project referred to as Reptile.
The analysis of the vermagic metadata revealed that it is compiled for a kernel version 5.10.112-108.499.amzn2.x86_64. The experts noticed that the rootkit has a limited set of features.
The attackers use shell commands to download the installer and a custom binary package from a remote server and install the implant and the rootkit.
The installer is written in C++, it takes the binary package as an argument and then extracts the rootkit as well as a server implant module.
The researchers noticed that the implant is currently under active development.
The malware configuration is encrypted using the RC4 algorithm in the two early samples, while authors used a simple xor with a single byte key (0x43) in the most recent sample analyzed by the experts.
The configuration format in the first sample contains all elements in encrypted form, while the most recent sample has only the C&C domain encrypted.
The implant supports two mechanisms of persistence, depending on the privileges of his execution. When it runs as the root user, it tries to write a line containing
sh -c IMPLANT_EXECUTABLE_NAME >/dev/null 2>& in the files
If it runs as a simple user, it will modify the following files:
The rootkit installer will insert the persistence for the kernel module in the /etc/rc.modules file.
The implant supports common backdoor commands, experts noticed the development of the backdoor
Mélofée can execute arbitrary commands, carry out file operations, Kill the current process and removes the persistance, create sockets, and launch a shell.
The researchers linked Mélofée to China-linked APT groups like APT41, and Earth Berberoka.
Below are evidence collected by the researchers that link Mélofée implants to China state-sponsored activity:
Researchers also pointed out that the HelloBot Linux malware family, linked to Winnti APT group, shared Mélofée infrastructure.
The experts also discovered another malware tracked as AlienReverse, which appears to be similar to Mélofée and includes public tools like tools EarthWorm and socks_proxy.
“The Mélofée implant family is another tool in the arsenal of chinese state sponsored attackers, which show constant innovation and development.” concludes the report.
“The capabilities offered by Mélofée are relatively simple, but may enable adversaries to conduct their attacks under the radar. These implants were not widely seen, showing that the attacker are likely limiting its usage to high value targets.”
Please vote for Security Affairs (https://securityaffairs.com/) as the best European Cybersecurity Blogger Awards 2022 – VOTE FOR YOUR WINNERS
Vote for me in the sections:
You can nominate yourself or your favourite blogger. We ask that you provide a brief paragraph of 250 words explaining why they should win.
Nominate here: https://docs.google.com/forms/d/e/1FAIpQLSfaFMkrMlrLhOBsRPKdv56Y4HgC88Bcji4V7OCxCm_OmyPoLw/viewform
Follow me on Twitter: @securityaffairs and Facebook and Mastodon
(SecurityAffairs – hacking, Mélofée)