Researchers at Cado Security Labs received an alert about a honeypot using the Docker Engine API. “A Docker command was received…” they write, “that spawned a new container, based on Alpine Linux, and created a bind mount for the underlying honeypot server’s root directory…”
Typically, this is exploited to write out a job for the Cron scheduler to execute… In this particular campaign, the attacker exploits this exact method to write out an executable at the path /usr/bin/vurl, along with registering a Cron job to decode some base64-encoded shell commands and execute them on the fly by piping through bash.
The vurl executable consists solely of a simple shell script function, used to establish a TCP connection with the attacker’s Command and Control (C2) infrastructure via the /dev/tcp device file. The Cron jobs mentioned above then utilise the vurl executable to retrieve the first stage payload from the C2 server… To provide redundancy in the event that the vurl payload retrieval method fails, the attackers write out an additional Cron job that attempts to use Python and the urllib2 library to retrieve another payload named t.sh
“Multiple user mode rootkits are deployed to hide malicious processes,” they note. And one of the shell scripts “makes use of the shopt (shell options) built-in to prevent additional shell commands from the attacker’s session from being appended to the history file… Not only are additional commands prevented from being written to the history file, but the shopt command itself doesn’t appear in the shell history once a new session has been spawned.”
The same script also inserts “an attacker-controlled SSH key to maintain access to the compromised host,” according to the article, retrieves a miner for the Monero cryptocurrency and then “registers persistence in the form of systemd services” for both the miner and an open source Golang reverse shell utility named Platypus.
It also delivers “various utilities,” according to the blog Security Week, “including ‘masscan’ for host discovery.” Citing CADO’s researchers, they write that the shell script also “weakens the machine by disabling SELinux and other functions and by uninstalling monitoring agents.”
The Golang payloads deployed in these attacks allow attackers to search for Docker images from the Ubuntu or Alpine repositories and delete them, and identify and exploit misconfigured or vulnerable Hadoop, Confluence, Docker, and Redis instances exposed to the internet… [“For the Docker compromise, the attackers spawn a container and escape from it onto the underlying host,” the researchers writes.]
“This extensive attack demonstrates the variety in initial access techniques available to cloud and Linux malware developers,” Cado notes. “It’s clear that attackers are investing significant time into understanding the types of web-facing services deployed in cloud environments, keeping abreast of reported vulnerabilities in those services and using this knowledge to gain a foothold in target environments.”
Read more of this story at Slashdot.
