Sophisticated Quasar Linux RAT Targets Software Developers

A recently identified Linux backdoor was designed to steal developer credentials across the software supply chain, Trend Micro warns. Dubbed Quasar Linux (QLNX), the RAT has a modular architecture, uses multiple persistence and detection evasion mechanisms, packs a rootkit, and provides attackers with remote access to the infected machines. The main purpose of QLNX, Trend Micro says, is the theft of developer credentials, keys, and tokens that could provide its operators with access to development tools, cloud environments, and repositories. It targets AWS credentials and configurations, Kubernetes tokens, Docker Hub credentials, Git access tokens and configurations, NPM authentication tokens, and PyPI API keys, potentially allowing operators to publish malicious packages through established developer accounts. “An attacker who successfully deploys QLNX against a package maintainer gains access to that maintainer’s publishing pipeline. A single compromise can be silently leveraged to trojanize packages, inject backdoors into build artifacts, or pivot into cloud environments where production infrastructure lives,” Trend Micro says. The RAT is executed in memory, spoofs its process name, and can delete itself to evade detection. It also performs system reconnaissance to detect containers, hides specific processes, ports, and files, and clears system logs. It also deploys a Pluggable Authentication Module (PAM) backdoor to harvest credentials, and gathers extensive system information, including clipboard contents, SSH keys, and browser profiles. QLNX contains two PAM backdoor implementations: the first harvests plaintext credentials from authentication events, contains a master password bypass, and logs outbound SSH session data; the second loads into dynamically linked processes to extract the service name, username, and authentication token. The malware contains a two-tier rootkit architecture, deploying userspace hooks through the LD_PRELOAD shared library, which also enables persistence, along with an eBPF rootkit controller that manages kernel-level BPF maps. “This component does not contain the kernel-side eBPF program itself. Its role is limited to creating and managing BPF maps — kernel data structures designed to hold the list of items that should be hidden from the system. Upon receiving instructions from the C&C server, the implant leverages the Linux kernel’s BPF subsystem to conceal processes, files, and network ports from standard userland tools,” Trend Micro explains. QLNX can achieve persistence in six different ways, using crontab entries, desktop entries, init scripts, service files, and shell lines, based on commands received from the operator, and can deploy several methods on the same system. The malware supports 58 distinct commands, allowing attackers to interact with shells, enumerate and manipulate files and processes, create directories, download and upload files, reboot or shut down the system, open URLs, display notifications, open TCP sockets, harvest sensitive information, capture the screen, log keystrokes, and use SSH credentials to execute commands on remote hosts. “The QLNX implant was built for long-term stealth and credential theft. What makes it particularly dangerous is not any single feature, but how its capabilities chain together into a coherent attack workflow: arrive, erase from disk, persist through six redundant mechanisms, hide at both userspace and kernel level, and then harvest the credentials that matter most,” Trend Micro notes. Related: Exploitation of ‘Copy Fail’ Linux Vulnerability Begins Related: Dozens of Open VSX Extension Clones Linked to GlassWorm Malware Related: New ‘SSHStalker’ Linux Botnet Uses Old Techniques Related: Checkmarx Confirms Data Stolen in Supply Chain Attack WRITTEN BY Ionut Arghire Ionut Arghire is an international correspondent for SecurityWeek. 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