[Upgrading, Modifying and Unlocking] presidentson:
I am a very happy owner of Huawei e8372h-153 that has firmware version 21.210.03.01.1080 and much less happy owner of similar device that has firmware version 21.333.03.00.00

I am looking to downgrade the 21.333.03.00.00 to 21.210.03.01.1080.

Is there a linux based way to dump firmware (and webui) from device 21.210 to file(s)? This would provide a backup before I start playing with these devices a little bit more...

Dumping the images is one important step in a backup procedure and restoring is as important :) There is more info available on that, but most solutions require Windows OS and a custom software. Is there a way to do it on linux using standard toolset (or optionally some custom tools, but these would need to have source code available for me to trust them).

I don't want to use images available on the network as I also can't trust them without verification and for that I would have to do lots of binwalking.

My initial goal is to replace/downgrade the firmware on the device 21.333 (and my ultimate goal is to get images that I can binwalk and learn from).

So far I have been able to explore these devices a bit

After connecting to USB device is shown (lsusb) as

12d1:1f01 Huawei Technologies Co., Ltd. E353/E3131 (Mass storage mode)

then two interesting devices appear /dev/sr0 (8MB mounted on /media/${USER}/MobileWiFi) and /dev/mmcblk0p1 (memory card partition mounted as /media/${USER}/1234-6789).

usb_modeswitch with option --huawei-alt-mode switches this device to

12d1:155e Huawei Technologies Co., Ltd. HUAWEI_MOBILE

then /dev/ttyUSB0, /dev/ttyUSB1 oraz /dev/ttyUSB2 appear in /dev (the first one allows for AT commands execution, function of the remaining TTYs is unclear to me, but I would love to find out soon)

usb_modeswitch with --huawei-new-mode option switches from device 12d1:1f01 to

12d1:14db Huawei Technologies Co., Ltd. E353/E3131

then only the memory card related devices appear and from what I understand the device is in hi-link mode (it is accessible from browser as 192.168.8.1)

after connecting with test pin number 2 connected to GND I get

12d1:1443 Huawei Technologies Co., Ltd. USB COM

here the device seems to be in boot mode (?) exposing only one TTY (/dev/ttyUSB0) that I have no clue how to use (as I want to avoid using any unverifiable software and Windows OS). BTW In this mode memory card partition also seems to be available.

My main question is: Where to search/explore from here to get dumps of firmware and webui partitions from the 21.210 device and restore from these (preferably also on 21.333 device -- fingers crossed).

Bonus question(s): Where one can learn more about the functionalities of /dev/ttyUSB1 and /dev/ttyUSB2 (in alt mode) and what is the /dev/sr0 (in storage mode) and how to use /dev/ttyUSB0 (in boot mode?

Any help/suggestions much appreciated :)

Below I include the output of the ^AAT^VERSION? command for both (21.210 and 21.333) devices

# DEVICE 21.210 (happy days)
^VERSION:BDT:Apr 13 2015, 19:43:32
^VERSION:EXTS:21.210.03.01.1080
^VERSION:INTS:21.210.03.01.1080
^VERSION:EXTD:WEBUI_17.100.09.02.1080
^VERSION:INTD:WEBUI_17.100.09.02.1080
^VERSION:EXTH:CL1E8372HM Ver.A
^VERSION:INTH:CL1E8372HM Ver.A
^VERSION:EXTU:E8372
^VERSION:INTU:E8372H-153
^VERSION:CFG:1005
^VERSION:PRL:
^VERSION:OEM:
^VERSION:INI:E8372hCUST-B01C00

# DEVICE 21.333 (devils' half)
^VERSION:BDT:Nov 13 2019, 09:37:21
^VERSION:EXTS:21.333.03.00.00
^VERSION:INTS:
^VERSION:EXTD:WEBUI_17.100.21.02.03_RE5
^VERSION:INTD:
^VERSION:EXTH:CL1E8372HM Ver.A
^VERSION:INTH:
^VERSION:EXTU:E8372
^VERSION:INTU:
^VERSION:CFG:1005
^VERSION:PRL:
^VERSION:OEM:
^VERSION:INI:E8372hCUST-B00C00