How Researchers Root Amazon Echo to Turn It Into a Stealthy Audio Spy

MWR security researchers identified a physical vulnerability in Amazon Echo that lets an attacker obtain a root shell on the device’s Linux‑based firmware, install persistent malware, and silently stream microphone audio to a remote server.

The flaw stems from two hardware design issues:

1. Exposed debug panel;
2. Hardware configuration permits booting from an external SD card;

The following guide shows how to root the Echo and convert it into a listening device.

Previous Work

Earlier security work demonstrated that inserting an SD card into the debug panel could boot the device into a generic Linux environment; the details and boot images are available on GitHub. Researchers also published reports on the feasibility of rooting the Echo.

Building on those findings, we extended the attack to boot the Echo’s real firmware, install a persistent backdoor, obtain a remote root shell, and achieve real‑time microphone eavesdropping.

Rooting the Device

Removing the rubber cover on the Echo reveals 18 test points on the debug panel.

Connecting to these UART points allows us to view boot logs and device configuration.

The Echo’s main MCU is a TI DM3725 digital media processor with an ARM Cortex‑A core. Its boot sequence consists of three stages: a minimal hardware configuration via bootrom, loading the second bootloader (X‑loader) into internal RAM, and finally loading U‑Boot, which then starts the kernel.

By default the Echo attempts to boot from an SD card attached to the debug panel (preferring internal eMMC). Modifying the board configuration can change this order.

Therefore, writing X‑loader and U‑Boot to an SD card with the correct partition layout lets the device boot from the card and drop into the U‑Boot command line.

The hidden ROM communicates with the SD card over SPI, so only the SPI‑compatible pins need to be wired.

SDMMC D0 → MISO SDMMC D3 → !SS SDMMC CMD → MOSI SDMMC CLOCK → SCK

Power the SDMMC pins with +3 V and connect a GND pin.

After booting from the prepared SD card, we can interrupt the boot process, access the U‑Boot console, and inspect the internal eMMC partitions. The eMMC contains eight partitions (xloader, recovery, boot, idme, diag, main‑A, main‑B, data). The main‑A and main‑B partitions hold the kernel and root filesystem and switch on firmware updates.

To identify the active partition we use U‑Boot commands:

uboot> mmc dev 1 uboot> ext4ls mmc 1:6 uboot> ext4ls mmc 1:7

Only one partition’s filesystem is visible at a time; a firmware update triggers the switch. Once the target partition is known, we modify U‑Boot to boot from it, adjust kernel parameters for a writable root, and launch /bin/sh instead of the normal init scripts.

With a root shell we bypass all authentication mechanisms.

Because the device reboots every few minutes, we start a watchdog process to reset the reboot timer:

After stabilizing the environment, we install a reverse‑shell script on the writable data partition and configure it to launch at boot via /etc/init.d/varlocal.sh, which runs late in the init sequence and can access the data partition.

After the reverse shell is installed, we remove the external SD card and UART cable, reboot the Echo, and the init script triggers the backdoor. Listening on port 1377 on the remote server provides a persistent root shell.

Audio Capture

Using Amazon’s own shmbuf_tool, we continuously write raw microphone audio to a FIFO pipe, stream it over TCP/IP to a remote server, and optionally play it back through speakers.

Sample script startStream.sh (shown in the image) launches the capture.

Commands to save the audio stream to the remote server or play it back are also provided (see accompanying images).

Vulnerability Mitigation

The flaw affects 2015 and 2016 Echo models; the 2017 revision has been patched.

Images of the vulnerable 2016 model (serial 23‑002518‑01) and the fixed 2017 model (serial 23‑002518‑02) are shown below.

References

1. https://github.com/echohacking/wiki/wiki/Echo 2. https://vanderpot.com/Clinton_Cook_Paper.pdf 3. https://www.theverge.com/circuitbreaker/2016/12/14/13955878/wynn-las-vegas-amazon-echo-hotel-room-privacy