Description
MCUboot's serial-recovery image-upload handler bs_upload() in boot/boot_serial/src/boot_serial.c declares const struct flash_area *fap = NULL and assigns it only via flash_area_open() part-way through the function. Two early validation failures (goto out_invalid_data) — a CBOR map that fails to decode, or an upload packet missing the off/data members — branch past the open while fap is still NULL, then fall into the shared epilogue. In MCUBOOT_ENC_IMAGES builds that epilogue unconditionally calls boot_handle_enc_fw(fap), which reaches boot_image_load_header() and flash_area_read() and dereferences the NULL flash_area.
The defect is reachable pre-authentication: the trigger is the very first serial-recovery upload command carrying a malformed payload. The guarding conditions are default-true on a fresh recovery session — img_num, curr_off and img_size are zero-initialized statics, so curr_off == img_size and the primary-slot test both hold. It requires a non-default build: encrypted images (MCUBOOT_ENC_IMAGES / Zephyr CONFIG_BOOT_ENCRYPT_IMAGE) together with an active serial-recovery transport, on the Zephyr or Mynewt port (the two that build both boot/boot_serial/src/boot_serial.c and boot_serial_encryption.c with MCUBOOT_ENC_IMAGES).
The impact is a transient denial of service of the bootloader during recovery. fap is a hard NULL rather than an attacker-controlled value, so there is no memory-corruption or information-leak primitive and image authentication is unaffected. Whether the dereference faults is platform-dependent — on targets where address 0x0 is mapped readable flash the read merely returns an error and execution continues, while targets that trap NULL (MPU / null-pointer-exception detection) take a hard fault. Because serial recovery is unauthenticated by design and already permits the console attacker to write the secondary slot, the added capability is only a low-value transient crash.
The related unconditional flash_area_close(fap) call in the same epilogue is a safe no-op on the ports that reach it, so it does not contribute to the dereference.
The affected ports are the Zephyr port — boot/zephyr/CMakeLists.txt compiles boot_serial.c under CONFIG_MCUBOOT_SERIAL and boot_serial_encryption.c under CONFIG_BOOT_ENCRYPT_IMAGE — and the Mynewt port, whose mcuboot_config.h defines MCUBOOT_SERIAL unconditionally and MCUBOOT_ENC_IMAGES under any BOOTUTIL_ENCRYPT_ syscfg, with boot/boot_serial/pkg.yml declaring no explicit source list so the whole directory is built. The Espressif port is not affected**: it compiles boot_serial.c but not boot_serial_encryption.c, and defines no MCUBOOT_ENC_IMAGES, so the #ifdef MCUBOOT_ENC_IMAGES block containing the call is preprocessed away. The NuttX, Cypress and Mbed ports do not build boot_serial.c at all.
The defect is reachable pre-authentication: the trigger is the very first serial-recovery upload command carrying a malformed payload. The guarding conditions are default-true on a fresh recovery session — img_num, curr_off and img_size are zero-initialized statics, so curr_off == img_size and the primary-slot test both hold. It requires a non-default build: encrypted images (MCUBOOT_ENC_IMAGES / Zephyr CONFIG_BOOT_ENCRYPT_IMAGE) together with an active serial-recovery transport, on the Zephyr or Mynewt port (the two that build both boot/boot_serial/src/boot_serial.c and boot_serial_encryption.c with MCUBOOT_ENC_IMAGES).
The impact is a transient denial of service of the bootloader during recovery. fap is a hard NULL rather than an attacker-controlled value, so there is no memory-corruption or information-leak primitive and image authentication is unaffected. Whether the dereference faults is platform-dependent — on targets where address 0x0 is mapped readable flash the read merely returns an error and execution continues, while targets that trap NULL (MPU / null-pointer-exception detection) take a hard fault. Because serial recovery is unauthenticated by design and already permits the console attacker to write the secondary slot, the added capability is only a low-value transient crash.
The related unconditional flash_area_close(fap) call in the same epilogue is a safe no-op on the ports that reach it, so it does not contribute to the dereference.
The affected ports are the Zephyr port — boot/zephyr/CMakeLists.txt compiles boot_serial.c under CONFIG_MCUBOOT_SERIAL and boot_serial_encryption.c under CONFIG_BOOT_ENCRYPT_IMAGE — and the Mynewt port, whose mcuboot_config.h defines MCUBOOT_SERIAL unconditionally and MCUBOOT_ENC_IMAGES under any BOOTUTIL_ENCRYPT_ syscfg, with boot/boot_serial/pkg.yml declaring no explicit source list so the whole directory is built. The Espressif port is not affected**: it compiles boot_serial.c but not boot_serial_encryption.c, and defines no MCUBOOT_ENC_IMAGES, so the #ifdef MCUBOOT_ENC_IMAGES block containing the call is preprocessed away. The NuttX, Cypress and Mbed ports do not build boot_serial.c at all.
Analysis
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Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | ||||||
|---|---|---|---|---|---|---|---|---|---|
| mcu-tools | mcuboot | unaffected |
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Remediation
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References
History
Fri, 13 Nov 2026 00:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | MCUboot's serial-recovery image-upload handler bs_upload() in boot/boot_serial/src/boot_serial.c declares const struct flash_area *fap = NULL and assigns it only via flash_area_open() part-way through the function. Two early validation failures (goto out_invalid_data) — a CBOR map that fails to decode, or an upload packet missing the off/data members — branch past the open while fap is still NULL, then fall into the shared epilogue. In MCUBOOT_ENC_IMAGES builds that epilogue unconditionally calls boot_handle_enc_fw(fap), which reaches boot_image_load_header() and flash_area_read() and dereferences the NULL flash_area. The defect is reachable pre-authentication: the trigger is the very first serial-recovery upload command carrying a malformed payload. The guarding conditions are default-true on a fresh recovery session — img_num, curr_off and img_size are zero-initialized statics, so curr_off == img_size and the primary-slot test both hold. It requires a non-default build: encrypted images (MCUBOOT_ENC_IMAGES / Zephyr CONFIG_BOOT_ENCRYPT_IMAGE) together with an active serial-recovery transport, on the Zephyr or Mynewt port (the two that build both boot/boot_serial/src/boot_serial.c and boot_serial_encryption.c with MCUBOOT_ENC_IMAGES). The impact is a transient denial of service of the bootloader during recovery. fap is a hard NULL rather than an attacker-controlled value, so there is no memory-corruption or information-leak primitive and image authentication is unaffected. Whether the dereference faults is platform-dependent — on targets where address 0x0 is mapped readable flash the read merely returns an error and execution continues, while targets that trap NULL (MPU / null-pointer-exception detection) take a hard fault. Because serial recovery is unauthenticated by design and already permits the console attacker to write the secondary slot, the added capability is only a low-value transient crash. The related unconditional flash_area_close(fap) call in the same epilogue is a safe no-op on the ports that reach it, so it does not contribute to the dereference. The affected ports are the Zephyr port — boot/zephyr/CMakeLists.txt compiles boot_serial.c under CONFIG_MCUBOOT_SERIAL and boot_serial_encryption.c under CONFIG_BOOT_ENCRYPT_IMAGE — and the Mynewt port, whose mcuboot_config.h defines MCUBOOT_SERIAL unconditionally and MCUBOOT_ENC_IMAGES under any BOOTUTIL_ENCRYPT_ syscfg, with boot/boot_serial/pkg.yml declaring no explicit source list so the whole directory is built. The Espressif port is not affected**: it compiles boot_serial.c but not boot_serial_encryption.c, and defines no MCUBOOT_ENC_IMAGES, so the #ifdef MCUBOOT_ENC_IMAGES block containing the call is preprocessed away. The NuttX, Cypress and Mbed ports do not build boot_serial.c at all. | |
| Title | Pre-authentication NULL pointer dereference in MCUboot serial-recovery image upload (encrypted-image builds) | |
| Weaknesses | CWE-476 | |
| References |
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| Metrics |
cvssV3_1
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MITRE
Status: PUBLISHED
Assigner: zephyr
Published:
Updated: 2026-11-13T00:23:03.881Z
Reserved: 2026-07-22T19:41:19.883Z
Link: CVE-2026-16659
Vulnrichment
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NVD
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Redhat
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OpenCVE Enrichment
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Weaknesses
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CWE-476
NULL Pointer Dereference