Firmware Loader and Application availability

RE: Firmware Loader and Application availability

Ramakrishnan — Tue, 04 Aug 2026 09:22:05 GMT

Agree. Its a question of which trade off to make. We are also evaluating if the application image has to be encrypted which necessitates mcuboot.

I think we can close this thread for now. I'll do some experimentation and come back again if there are more questions.

Thanks.

RE: Firmware Loader and Application availability

Vidar Berg — Tue, 04 Aug 2026 09:10:56 GMT

Yes, I don't have a right answer to give here other than that there are tradeoffs to be made. A minimal immutable bootloader should have a limited attack surface, and for any vulnerabilities uncovered in the future, I imagine it may be possible to apply mitigations for them in the firmware loader (depending on what the vulnerability is).

RE: Firmware Loader and Application availability

Ramakrishnan — Tue, 04 Aug 2026 08:55:38 GMT

Okay. Thanks for the clarification.

From security standpoint, there are concerns with mcuboot not being upgradeable as it looks like there were some CVEs against mcuboot. So not sure about taking that route.

RE: Firmware Loader and Application availability

Vidar Berg — Tue, 04 Aug 2026 08:47:43 GMT

Supporting this configuration will likely require some modifications to the bootloader logic. I do not see any samples or tests that cover this configuration. If reducing the memory footprint is the main concern, I would suggest using MCUboot as a minimal immutable bootloader and instead considering support for updating the firmware loader.

https://nrfconnectdocs.nordicsemi.com/ncs/latest/nrf/app_dev/bootloaders_dfu/mcuboot_nsib/bootloader_adding_sysbuild.html#update-of-the-firmware-loader-image

RE: Firmware Loader and Application availability

Ramakrishnan — Mon, 03 Aug 2026 12:05:56 GMT

Thanks for the prompt response and those options. They look promising. Will investigate those.

As a follow up, if we choose single slot DFU with firmware loader, is it also possible to have an upgradeable mcuboot ?

Currently we have B0 + mcuboot ( s0 and s1 ) + application ( primary and secondary ) partitions and with swap-move algorithm. We are doing mcuboot upgrade by following same DFU procedure as that of the application and internally mcuboot takes care of identifying the image in secondary slot to be an mcuboot image and does what is needed.

Is it possible to realize the same 2 stage bootloader with an upgradeable mcuboot with single slot DFU + firmware loader ?

RE: Firmware Loader and Application availability

Vidar Berg — Mon, 03 Aug 2026 11:56:42 GMT

Hello,

It is also possible to have MCUboot enter the firmware loader after a pin reset by enabling CONFIG_BOOT_FIRMWARE_LOADER_PIN_RESET setting, if that helps. Another option you may consider is changing the boot mode through the retention subsystem after a fatal error by overriding the fatal error handler, which is declared as __WEAK. This should help mitigate the risk of a non-functional application causing the device to become bricked.

Best regards,

Vidar