How to UnBrick Your Firewall Devices in Linksys WRT 1200 1900 and 3200

Reading Time: 3 minutes

(From Top Left) TFTPd server running inside virtualbox with a bridged adapter. Putty running in linux mint with the Venom console activated. (From Bottom Left) Linksys WRT32X with a USB to TTL cable from left to right black, white green pins inserted.

In this guide we use a linux mint host running windows in a virtual box.

1 Setup the TFTPd Server

Download the windows tFTPd installer here https://pjo2.github.io/tftpd64/

Setup a bridged adapter on guest virtual box.

Connect a LAN cable from your computer to LAN1 on the linksys device.

Set host network adapter to 192.168.1.3, 255.255.255.0 for the mask, 192.168.1.1 for the gateway.

Setup guest additions.

Setup a shared folder that is auto mounted. Point it to the location of your firmware image on your linux host.

Configure the windows network adapter. Set it to 192.168.1.2, 255.255.255.0 for the mask, 192.168.1.1 for the gateway.

Configure the guest tFTPd server. Make sure you select the correct service interface 192.168.1.2. Browse the current directory to the location of the mounted shared host folder.

TFTPd server is configured on the Z drive which is the guest addition shared host folder. There lies the firmware images. What we see here is also the Venom console showing successful flash writes.

2 Setup the USB to TTL Connection

The white socket service port is located on the front right hand side of the device. PINS from left to right; Black (ground), White(RX), skip a pin, Green(TX). DO NOT USE the red pin, it is 5 volts and will fry your board.

Unplug your USB adapter cable. Search for connected serial devices; –

$ ls /dev/ttyUSB*

Above is the device path to your USB cable.

Install putty; –

sudo apt install putty

Add dialout to your current user. Log out and and log back in to create a new session.

sudo usermod -aG dailout current_user

Run putty. Configure as per below details.

Set flow control to None so that you can type into the Putty telnet console.

The device path on the host linux machine is /dev/ttyUSB0. Set speed to 115200. Connection type must be serial / telnet. Save this profile.

The screen should just be blank.

Now turn on the router.

It should just hang with the LAN1 blue light activated.

Now press spacebar on the telnet screen with one hand, while half disconnecting/reconnecting the 3 pins, with another hand.

You should now get the Venom console prompt.

If you do not, reboot the router and repeat the two handed procedure.

On the venom prompt type the below to flash your router.

setenv ipaddr 192.168.1.1
setenv serverip 192.168.1.2
setenv firmwareName wrt.img
run update_both_images

wrt.img above must exist in the shared Z folder in the windows guest machine.

In my setup i failed flashing the OEM image, but the openwrt images worked.

More Guides with the 1200 1900 and 3200 Family

Below are videos that helped me write this article and unbrick my device. I had to read the comments to see how other people activated their Venom prompt.