Skill v1.0.1

currentLLM-judged scan95/100

mukul975/anthropic-cybersecurity-skills/analyzing-linux-system-artifacts

+3 new

──Details

PublishedAugust 9, 2026 at 11:43 PM

Content Hashsha256:6e8d44dc4f4a5c60...

Git SHA4c0b700ac5d2

Bump Typepatch

Compare with v1.0.0

──Files

Files (1 file, 14.6 KB)

SKILL.md14.6 KBactive

SKILL.md · 340 lines · 14.6 KB

name: analyzing-linux-system-artifacts description: Examine Linux system artifacts (auth logs, cron/systemd persistence, shell history, SSH keys, and system configuration) to uncover evidence of compromise, detect rootkits or backdoors, and reconstruct user/attacker activity. Use when investigating a compromised Linux server or workstation, hunting for persistence mechanisms, or scoping a Linux-based breach during incident response. domain: cybersecurity subdomain: digital-forensics tags:

forensics
linux-forensics
system-artifacts
log-analysis
persistence-detection
incident-investigation

version: '1.0' author: mahipal license: Apache-2.0 nist_csf:

RS.AN-03
DE.AE-02
RS.MA-01

mitre_attack:

T1070
T1059.004
T1543.002
T1053.003

Analyzing Linux System Artifacts

When to Use

When investigating a compromised Linux server or workstation
For identifying persistence mechanisms (cron, systemd, SSH keys)
When tracing user activity through shell history and authentication logs
During incident response to determine the scope of a Linux-based breach
For detecting rootkits, backdoors, and unauthorized modifications

Prerequisites

Forensic image or live access to the Linux system (read-only)
Understanding of Linux file system hierarchy (FHS)
Knowledge of common Linux logging locations (/var/log/)
Tools: chkrootkit, rkhunter, AIDE, auditd logs
Familiarity with systemd, cron, and PAM configurations
Root access for complete artifact collection

Workflow

Step 1: Mount and Collect System Artifacts

bash

# Mount forensic image read-only
mount -o ro,loop,offset=$((2048*512)) /cases/case-2024-001/images/linux_evidence.dd /mnt/evidence
 
# Create collection directories
mkdir -p /cases/case-2024-001/linux/{logs,config,users,persistence,network}
 
# Collect authentication logs
cp /mnt/evidence/var/log/auth.log* /cases/case-2024-001/linux/logs/
cp /mnt/evidence/var/log/secure* /cases/case-2024-001/linux/logs/
cp /mnt/evidence/var/log/syslog* /cases/case-2024-001/linux/logs/
cp /mnt/evidence/var/log/kern.log* /cases/case-2024-001/linux/logs/
cp /mnt/evidence/var/log/audit/audit.log* /cases/case-2024-001/linux/logs/
cp /mnt/evidence/var/log/wtmp /cases/case-2024-001/linux/logs/
cp /mnt/evidence/var/log/btmp /cases/case-2024-001/linux/logs/
cp /mnt/evidence/var/log/lastlog /cases/case-2024-001/linux/logs/
cp /mnt/evidence/var/log/faillog /cases/case-2024-001/linux/logs/
 
# Collect user artifacts
for user_dir in /mnt/evidence/home/*/; do
    username=$(basename "$user_dir")
    mkdir -p /cases/case-2024-001/linux/users/$username
    cp "$user_dir"/.bash_history /cases/case-2024-001/linux/users/$username/ 2>/dev/null
    cp "$user_dir"/.zsh_history /cases/case-2024-001/linux/users/$username/ 2>/dev/null
    cp -r "$user_dir"/.ssh/ /cases/case-2024-001/linux/users/$username/ 2>/dev/null
    cp "$user_dir"/.bashrc /cases/case-2024-001/linux/users/$username/ 2>/dev/null
    cp "$user_dir"/.profile /cases/case-2024-001/linux/users/$username/ 2>/dev/null
    cp "$user_dir"/.viminfo /cases/case-2024-001/linux/users/$username/ 2>/dev/null
    cp "$user_dir"/.wget-hsts /cases/case-2024-001/linux/users/$username/ 2>/dev/null
    cp "$user_dir"/.python_history /cases/case-2024-001/linux/users/$username/ 2>/dev/null
done
 
# Collect root user artifacts
cp /mnt/evidence/root/.bash_history /cases/case-2024-001/linux/users/root/ 2>/dev/null
cp -r /mnt/evidence/root/.ssh/ /cases/case-2024-001/linux/users/root/ 2>/dev/null
 
# Collect system configuration
cp /mnt/evidence/etc/passwd /cases/case-2024-001/linux/config/
cp /mnt/evidence/etc/shadow /cases/case-2024-001/linux/config/
cp /mnt/evidence/etc/group /cases/case-2024-001/linux/config/
cp /mnt/evidence/etc/sudoers /cases/case-2024-001/linux/config/
cp -r /mnt/evidence/etc/sudoers.d/ /cases/case-2024-001/linux/config/
cp /mnt/evidence/etc/hosts /cases/case-2024-001/linux/config/
cp /mnt/evidence/etc/resolv.conf /cases/case-2024-001/linux/config/
cp -r /mnt/evidence/etc/ssh/ /cases/case-2024-001/linux/config/

Step 2: Analyze User Accounts and Authentication

bash

# Analyze user accounts for anomalies
python3 << 'PYEOF'
print("=== USER ACCOUNT ANALYSIS ===\n")
 
# Parse /etc/passwd
with open('/cases/case-2024-001/linux/config/passwd') as f:
    for line in f:
        parts = line.strip().split(':')
        if len(parts) >= 7:
            username, _, uid, gid, comment, home, shell = parts[0], parts[1], int(parts[2]), int(parts[3]), parts[4], parts[5], parts[6]
 
            # Flag accounts with UID 0 (root equivalent)
            if uid == 0 and username != 'root':
                print(f"  ALERT: UID 0 account: {username} (shell: {shell})")
 
            # Flag accounts with login shells that shouldn't have them
            if shell not in ('/bin/false', '/usr/sbin/nologin', '/bin/sync') and uid >= 1000:
                print(f"  User: {username} (UID:{uid}, Shell:{shell}, Home:{home})")
 
            # Flag system accounts with login shells
            if uid < 1000 and uid > 0 and shell in ('/bin/bash', '/bin/sh', '/bin/zsh'):
                print(f"  WARNING: System account with shell: {username} (UID:{uid}, Shell:{shell})")
 
# Parse /etc/shadow for account status
print("\n=== PASSWORD STATUS ===")
with open('/cases/case-2024-001/linux/config/shadow') as f:
    for line in f:
        parts = line.strip().split(':')
        if len(parts) >= 3:
            username = parts[0]
            pwd_hash = parts[1]
            last_change = parts[2]
 
            if pwd_hash and pwd_hash not in ('*', '!', '!!', ''):
                hash_type = 'Unknown'
                if pwd_hash.startswith('$6$'): hash_type = 'SHA-512'
                elif pwd_hash.startswith('$5$'): hash_type = 'SHA-256'
                elif pwd_hash.startswith('$y$'): hash_type = 'yescrypt'
                elif pwd_hash.startswith('$1$'): hash_type = 'MD5 (WEAK)'
                print(f"  {username}: {hash_type} hash, last changed: day {last_change}")
PYEOF
 
# Analyze login history
last -f /cases/case-2024-001/linux/logs/wtmp > /cases/case-2024-001/linux/analysis/login_history.txt
lastb -f /cases/case-2024-001/linux/logs/btmp > /cases/case-2024-001/linux/analysis/failed_logins.txt 2>/dev/null

Step 3: Examine Persistence Mechanisms

bash

# Check cron jobs for all users
echo "=== CRON JOBS ===" > /cases/case-2024-001/linux/persistence/cron_analysis.txt
 
# System cron
for cronfile in /mnt/evidence/etc/crontab /mnt/evidence/etc/cron.d/*; do
    echo "--- $cronfile ---" >> /cases/case-2024-001/linux/persistence/cron_analysis.txt
    cat "$cronfile" 2>/dev/null >> /cases/case-2024-001/linux/persistence/cron_analysis.txt
    echo "" >> /cases/case-2024-001/linux/persistence/cron_analysis.txt
done
 
# User cron tabs
for cronfile in /mnt/evidence/var/spool/cron/crontabs/*; do
    echo "--- User crontab: $(basename $cronfile) ---" >> /cases/case-2024-001/linux/persistence/cron_analysis.txt
    cat "$cronfile" 2>/dev/null >> /cases/case-2024-001/linux/persistence/cron_analysis.txt
    echo "" >> /cases/case-2024-001/linux/persistence/cron_analysis.txt
done
 
# Check systemd services for persistence
echo "=== SYSTEMD SERVICES ===" > /cases/case-2024-001/linux/persistence/systemd_analysis.txt
find /mnt/evidence/etc/systemd/system/ -name "*.service" -newer /mnt/evidence/etc/os-release \
   >> /cases/case-2024-001/linux/persistence/systemd_analysis.txt
 
for svc in /mnt/evidence/etc/systemd/system/*.service; do
    echo "--- $(basename $svc) ---" >> /cases/case-2024-001/linux/persistence/systemd_analysis.txt
    cat "$svc" >> /cases/case-2024-001/linux/persistence/systemd_analysis.txt
    echo "" >> /cases/case-2024-001/linux/persistence/systemd_analysis.txt
done
 
# Check authorized SSH keys (backdoor detection)
echo "=== SSH AUTHORIZED KEYS ===" > /cases/case-2024-001/linux/persistence/ssh_keys.txt
find /mnt/evidence/home/ /mnt/evidence/root/ -name "authorized_keys" -exec sh -c \
   'echo "--- {} ---"; cat {}; echo ""' \; >> /cases/case-2024-001/linux/persistence/ssh_keys.txt
 
# Check rc.local and init scripts
cat /mnt/evidence/etc/rc.local 2>/dev/null > /cases/case-2024-001/linux/persistence/rc_local.txt
 
# Check /etc/profile.d/ for login-triggered scripts
ls -la /mnt/evidence/etc/profile.d/ > /cases/case-2024-001/linux/persistence/profile_scripts.txt
 
# Check for LD_PRELOAD hijacking
grep -r "LD_PRELOAD" /mnt/evidence/etc/ 2>/dev/null > /cases/case-2024-001/linux/persistence/ld_preload.txt
cat /mnt/evidence/etc/ld.so.preload 2>/dev/null >> /cases/case-2024-001/linux/persistence/ld_preload.txt

Step 4: Analyze Shell History and Command Execution

bash

# Analyze bash history for each user
python3 << 'PYEOF'
import os, glob
 
print("=== SHELL HISTORY ANALYSIS ===\n")
 
suspicious_commands = [
    'wget', 'curl', 'nc ', 'ncat', 'netcat', 'python -c', 'python3 -c',
    'perl -e', 'base64', 'chmod 777', 'chmod +s', '/dev/tcp', '/dev/udp',
    'nmap', 'masscan', 'hydra', 'john', 'hashcat', 'passwd', 'useradd',
    'iptables -F', 'ufw disable', 'history -c', 'rm -rf /', 'dd if=',
    'crontab', 'at ', 'systemctl enable', 'ssh-keygen', 'scp ', 'rsync',
    'tar czf', 'zip -r', 'openssl enc', 'gpg --encrypt', 'shred',
    'chattr', 'setfacl', 'awk', '/tmp/', '/dev/shm/'
]
 
for hist_file in glob.glob('/cases/case-2024-001/linux/users/*/.bash_history'):
    username = hist_file.split('/')[-2]
    print(f"User: {username}")
 
    with open(hist_file, 'r', errors='ignore') as f:
        lines = f.readlines()
 
    print(f"  Total commands: {len(lines)}")
    flagged = []
    for i, line in enumerate(lines):
        line = line.strip()
        for cmd in suspicious_commands:
            if cmd in line.lower():
                flagged.append((i+1, line))
                break
 
    if flagged:
        print(f"  Suspicious commands: {len(flagged)}")
        for lineno, cmd in flagged:
            print(f"    Line {lineno}: {cmd[:120]}")
    print()
PYEOF

Step 5: Check for Rootkits and Modified Binaries

bash

# Check for known rootkit indicators
# Compare system binary hashes against known-good
find /mnt/evidence/usr/bin/ /mnt/evidence/usr/sbin/ /mnt/evidence/bin/ /mnt/evidence/sbin/ \
   -type f -executable -exec sha256sum {} \; > /cases/case-2024-001/linux/analysis/binary_hashes.txt
 
# Check for SUID/SGID binaries (potential privilege escalation)
find /mnt/evidence/ -perm -4000 -type f 2>/dev/null > /cases/case-2024-001/linux/analysis/suid_files.txt
find /mnt/evidence/ -perm -2000 -type f 2>/dev/null > /cases/case-2024-001/linux/analysis/sgid_files.txt
 
# Check for suspicious files in /tmp and /dev/shm
find /mnt/evidence/tmp/ /mnt/evidence/dev/shm/ -type f 2>/dev/null \
   -exec file {} \; > /cases/case-2024-001/linux/analysis/tmp_files.txt
 
# Check for hidden files and directories
find /mnt/evidence/ -name ".*" -not -path "*/\." -type f 2>/dev/null | \
   head -100 > /cases/case-2024-001/linux/analysis/hidden_files.txt
 
# Check kernel modules
ls -la /mnt/evidence/lib/modules/$(ls /mnt/evidence/lib/modules/ | head -1)/extra/ 2>/dev/null \
   > /cases/case-2024-001/linux/analysis/extra_modules.txt
 
# Check for modified PAM configuration (authentication backdoors)
diff /mnt/evidence/etc/pam.d/ /cases/baseline/pam.d/ 2>/dev/null \
   > /cases/case-2024-001/linux/analysis/pam_changes.txt

Key Concepts

Concept	Description
/var/log/auth.log	Primary authentication log on Debian/Ubuntu systems
/var/log/secure	Primary authentication log on RHEL/CentOS systems
wtmp/btmp	Binary logs recording successful and failed login sessions
.bash_history	User command history file (can be cleared by attackers)
crontab	Scheduled task system commonly used for persistence
authorized_keys	SSH public keys granting passwordless access to an account
SUID bit	File permission allowing execution as the file owner (privilege escalation vector)
LD_PRELOAD	Environment variable that loads a shared library before all others (hooking technique)

Tools & Systems

Tool	Purpose
chkrootkit	Rootkit detection scanner for Linux systems
rkhunter	Rootkit Hunter - checks for rootkits, backdoors, and local exploits
AIDE	Advanced Intrusion Detection Environment - file integrity monitor
auditd	Linux audit framework for system call and file access monitoring
last/lastb	Parse wtmp/btmp for login and failed login history
Plaso/log2timeline	Super-timeline creation including Linux artifacts
osquery	SQL-based system querying for live forensic investigation
Velociraptor	Endpoint agent with Linux artifact collection capabilities

Common Scenarios

Scenario 1: SSH Brute Force Followed by Compromise Analyze auth.log for failed SSH attempts followed by success, identify the attacking IP, check .bash_history for post-compromise commands, examine authorized_keys for added backdoor keys, check crontab for persistence, review network connections.

Scenario 2: Web Server Compromise via Application Vulnerability Examine web server access and error logs for exploitation attempts, check /tmp and /dev/shm for webshells, analyze the web server user's activity (www-data), check for privilege escalation via SUID binaries or kernel exploits, review outbound connections.

Scenario 3: Insider Threat on Database Server Analyze the suspect user's bash_history for database dump commands, check for large tar/zip files in home directory or /tmp, examine scp/rsync commands for data transfer, review cron jobs for automated exfiltration, check USB device logs.

Scenario 4: Crypto-Miner on Cloud Instance Check for high-CPU processes in /proc (live) or systemd service files, examine crontab entries for miner restart scripts, check /tmp for mining binaries, analyze network connections for mining pool communications, review authorized_keys for attacker access.

Output Format

Linux Forensics Summary:
  System: webserver01 (Ubuntu 22.04 LTS)
  Hostname: webserver01.corp.local
  Kernel: 5.15.0-91-generic
 
  User Accounts:
    Total: 25 (3 with UID 0 - 1 ANOMALOUS)
    Interactive shells: 8 users
    Recently created: admin2 (created 2024-01-15)
 
  Authentication Events:
    Successful SSH logins: 456
    Failed SSH attempts: 12,345 (from 23 unique IPs)
    Sudo executions: 89
 
  Persistence Mechanisms Found:
    Cron jobs: 3 suspicious (reverse shell, miner restart)
    Systemd services: 1 unknown (update-checker.service)
    SSH keys: 2 unauthorized keys in root authorized_keys
    rc.local: Modified with download cradle
 
  Suspicious Activity:
    - bash_history contains wget to pastebin URL
    - SUID binary /tmp/.hidden/escalate found
    - /dev/shm/ contains compiled ELF binary
    - LD_PRELOAD in /etc/ld.so.preload pointing to /lib/.hidden.so
 
  Report: /cases/case-2024-001/linux/analysis/

← v1.0.0 All versions