RedTail Malware Payload Analysis and Linux Behavior

RedTail is a multi-architecture Linux malware family with capabilities for extensive host profiling and process masquerading. It establishes persistence through crontabs, modifies host firewall rules, and attempts to interfere with monitoring tools by terminating processes such as inotify and strace . The malware also generates network traffic over DNS-over-TLS on TCP port 853 to potentially reach remote infrastructure.

An analyst conducted dynamic analysis of an x86-64 RedTail sample inside an isolated Ubuntu 24.04 environment. The investigation compared root-privileged and unprivileged execution, used Proxmox/QEMU for memory forensics, and monitored syscalls with strace and auditd . Observed behavior included consistent host profiling, process renaming to php-fpm , and creation of @reboot cron entries.

Organizations should enforce the principle of least privilege to reduce the malware’s ability to modify system-level crontabs or firewall rules. Security teams should monitor for suspicious process masquerading, including legitimate service names such as php-fpm executing from unexpected paths. EDR solutions should also detect SIGKILL signals targeting security monitoring processes.

If RedTail activity is detected, affected Linux hosts should be isolated immediately to prevent lateral movement or additional command-and-control communication. Responders should perform memory forensics to identify masqueraded processes and inspect crontabs for unauthorized @reboot entries. Network logs should also be reviewed for anomalous outbound connections on TCP port 853 and iptables configurations checked for unauthorized rule changes.

Prerequisite: The Telemetry & Baseline Pre-flight Check must have passed.

Rationale: This section details the precise execution of the adversary technique (TTP) designed to trigger the detection rule. The commands and narrative MUST directly reflect the TTPs identified and aim to generate the exact telemetry expected by the detection logic. Abstract or unrelated examples will lead to misdiagnosis.

Attack Narrative & Commands: The adversary has deployed a specialized malware sample named redtail.x86_64 inside a specific directory structure /analysis/run-002/sample/ . To prevent security analysts from debugging its execution or using strace to observe its network communications and file modifications, the malware proactively scans for the existence of the strace utility. Upon finding a strace process, the malware issues a SIGKILL (Signal 9) to the strace PID, effectively terminating the analysis tool instantly and silently.

Attack Narrative & Commands: The adversary has deployed a specialized malware sample named redtail.x86_64 inside a specific directory structure /analysis/run-002/sample/ . To prevent security analysts from debugging its execution or using strace to observe its network communications and file modifications, the malware proactively scans for the existence of the strace utility. Upon finding a strace process, the malware issues a SIGKILL (Signal 9) to the strace PID, effectively terminating the analysis tool instantly and silently.

Regression Test Script: #!/bin/bash # Setup simulation directory structure mkdir -p /analysis/run-002/sample/ # Create a fake malware binary to match the detection logic path echo -e '#!/bin/bashnstrace sleep 100 & nsleep 1nkill -9 $!' > /analysis/run-002/sample/redtail.x86_64 chmod +x /analysis/run-002/sample/redtail.x86_64 # Start strace on a benign process in the background strace sleep 100 & STRACE_PID=$! echo "[+] Started strace with PID: $STRACE_PID" # Wait for strace to initialize sleep 2 # Execute the "malware" which will kill the strace process echo "[+] Executing simulated RedTail malware..." /analysis/run-002/sample/redtail.x86_64 # Verify if strace is dead if ! kill -0 $STRACE_PID 2>/dev/null; then echo "[+] Success: strace process was terminated." else echo "[-] Failure: strace process is still running." fi

Regression Test Script:

Cleanup Commands: # Remove the simulated malware and directory structure rm -rf /analysis/run-002/ # Kill any remaining sleep processes pkill -f "sleep 100"

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