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Thanks to the help of many of you, I have been able to unpack (with FMK), modify some of the files in the rootFS, and repack it (also using FMK).

For a reason that I cannot figure out, I cannot upload the modified firmware to the device.
Things I have tried:

  • Uploading modified firmware (Upload doesn't even start, the webapp tells me that the firmware update has failed)
  • Uploading unpack/repacked firmware with ZERO changes (Upload doesn't even start, the webapp tells me that the firmware update has failed)
  • Uploading firmware from manufacture (Uploads fine, and and update is applied to system, no problems)

Observations

When I take the original firmware and just unpack/repack, it is the same size as the original firmware file, but does not hash the same. I'm wondering if there is a checksum somewhere that the firmware update utility uses that fmk does to account for.

I am lost on what to try next. Any ideas or tutorials that you could point me to would really be appreciated.

UPDATE Doing some further investigation, i ran both firmwares (original and repacked original) through a hex diff. I noticed that in the original firmware, everwhere that "0x00 0x01" occurs, in the repacked version, it is replaced with a "0x80 0x00".

I'm hoping that this means something to someone...

Thanks

  • Since it fails immediately, it sounds like it's at least looking for a certain byte signature that it's not finding. Did you try changing all instances of 0x80 0x00 with the 0x00 0x01 you found, then attempt uploading? Also, I'm not sure how the file is formatted, but something else to try is if you can identify a potentially arbitrary byte to change in the original version (preferably somewhere that isn't where a checksum might be), you can upload that (original version with only one byte changed) to see what happens. – dsasmblr Jul 21 '17 at 19:49
  • I would suggest you to open an issue with FMK, since apparently it does not repack properly. Hopefully they also know more about possible checksums in the image and can fix the repacker to account for that. – Igor Skochinsky Jul 21 '17 at 21:17

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