GL-XE300 External Boot for Filesystem Imaging

I'm working with some GL-XE300 modems right now for a project. But I have reason to believe one of them is compromised.

Is there a way for me to run openwrt externally (Off USB or SD Card), so I can make as clean a copy as possible of the filesystem?

Thank you.

You can use exroot. Pls have a try.

I doubt it will work since the bootloader does not support booting of a different device, imho.

You can create an image of the whole storage by using dd and compare checksums then, if you like. If it is really tampered you will need to reflash the whole firmware using uboot anyway

exroot seems to require booting the device normally. Trying to avoid doing that.

I am looking at failsafe mode though and I'm seeing the board appears to have points for a serial connection. Would that work, and what would be the baud rate if it would?

The router has to boot normally. Then you set up exroot and all the changes will be in the USB.
When it has problems, you just unplug the USB and it will boot normal to the simple firmware.

If you want to clear the "normal firmware" totally and put everything including kernel etc to external storage, it is not possible.