plurigrid/asi/analyzing-persistence-mechanisms-in-linux

Analyzing Persistence Mechanisms in Linux

Overview

Adversaries establish persistence on Linux systems through crontab jobs, systemd service/timer units, LD_PRELOAD library injection, shell profile modifications (.bashrc, .profile), SSH authorized_keys 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 LD_PRELOAD Hijacking — Check /etc/ld.so.preload and LD_PRELOAD 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