Analyzing Persistence Mechanisms in Linux

Overview

Adversaries establish persistence on Linux systems through crontab jobs, systemd service/timer units, LDPRELOAD library injection, shell profile modifications (.bashrc, .profile), SSH authorizedkeys backdoors, and init script manipulation. This skill scans for all known persistence vectors, checks file timestamps and integrity, and correlates findings with auditd logs to build a timeline of persistence installation.

When to Use

• When investigating security incidents that require analyzing persistence mechanisms in linux
• When building detection rules or threat hunting queries for this domain
• When SOC analysts need structured procedures for this analysis type
• When validating security monitoring coverage for related attack techniques

Prerequisites

• Root or sudo access on target Linux system (or forensic image)
• auditd configured with file watch rules on persistence paths
• Python 3.8+ with standard library (os, subprocess, json)
• Optional: OSSEC/Wazuh agent for file integrity monitoring alerts

Steps

1. Scan Crontab Entries — Enumerate all user crontabs, /etc/cron.d/, /etc/cron.daily/, and anacron jobs for suspicious commands
2. Audit Systemd Units — Check /etc/systemd/system/ and ~/.config/systemd/user/ for non-package-managed service and timer units
3. Detect LDPRELOAD Hijacking — Check /etc/ld.so.preload and LDPRELOAD environment variable for injected shared libraries
4. Inspect Shell Profiles — Scan .bashrc, .bash_profile, .profile, /etc/profile.d/ for injected commands or reverse shells
5. Check SSH Authorized Keys — Audit all authorized_keys files for unauthorized public keys with command restrictions
6. Correlate Auditd Logs — Search auditd logs for file modification events on persistence paths to build an installation timeline
7. Generate Persistence Report — Produce a risk-scored report of all discovered persistence mechanisms

Expected Output

• JSON report of all persistence mechanisms found with risk scores
• Timeline of persistence installation from auditd correlation
• MITRE ATT&CK technique mapping (T1053, T1543, T1574, T1546)
• Remediation commands for each detected persistence mechanism