---
id: "CVE-2026-16664"
page: "https://infrastack.ai/live/CVE-2026-16664"
kind: "vulnerability"
aliases: ["CVE-2026-16664"]
title: "MCUboot: serial recovery upload reads out of bounds, crashing the bootloader"
severity: "medium"
cvss: 5.1
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["embedded", "firmware", "mcuboot", "runtime", "zephyr"]
not_affected_if: ["direct-image-upload", "no-serial-recovery", "single-application-slot"]
published_at: "2026-11-13T02:18:57+00:00"
first_seen_at: "2026-11-13T02:41:37+00:00"
updated_at: "2026-11-13T02:43:02+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-16664", "first_seen_at": "2026-11-13T02:41:37+00:00"}]
exploit_sources: []
---

# MCUboot: serial recovery upload reads out of bounds, crashing the bootloader

Link for people: https://infrastack.ai/live/CVE-2026-16664 (this .md is for agents)

MCUboot's Zephyr serial recovery handler accepts an unchecked image index in MCUmgr upload requests, which indexes past a flash slot table. An attacker with access to the unauthenticated serial recovery console can crash the bootloader, and in rare cases write to a partition outside the image set.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check whether the device runs MCUboot on Zephyr with serial recovery enabled and `MCUBOOT_SERIAL_DIRECT_IMAGE_UPLOAD` disabled
- Check the MCUboot version in use against the fixed versions in the product data

## Timeline

- 2026-11-13T02:41:37+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-16664

## Documents

- [advisory] Vendor advisory: github.com https://github.com/mcu-tools/mcuboot/security/advisories/GHSA-8rcq-2mgr-fhp8
- [fix] Patch: github.com https://github.com/mcu-tools/mcuboot/commit/183a05f256bdbbac86edcb048958da59018f814e

## From the sources

MCUboot's Zephyr serial-recovery upload handler bs_upload() in boot/boot_serial/src/boot_serial.c decodes the host-supplied image field of an MCUmgr image-upload request into img_num (a full 32-bit value) and latches it on the off == 0 packet without any range check. It then passes img_num straight to flash_area_id_from_multi_image_slot(img_num, 0), which on the Zephyr port resolves to __flash_area_ids_for_slot() in boot/zephyr/include/sysflash/sysflash.h and indexes the static const int all_slots[] table as all_slots[img_num  2]. That table holds only MCUBOOT_IMAGE_NUMBER  2 entries, so any img_num >= MCUBOOT_IMAGE_NUMBER is an out-of-bounds read.

The path is reachable by anyone with access to the serial / SMP recovery console, which is unauthenticated by design, and the bad value is supplied before any image signature is verified. The defect is specific to the default non-direct upload path (MCUBOOT_SERIAL_DIRECT_IMAGE_UPLOAD disabled) on the Zephyr port with the array-backed slot layout (not CONFIG_SINGLE_APPLICATION_SLOT). It is not gated on a multi-image configuration: MCUBOOT_IMAGE_NUMBER defaults to 1, so even a default single-image build is affected for any image >= 1. The MCUBOOT_SERIAL_DIRECT_IMAGE_UPLOAD path is safe (its flash_area_id_from_direct_image() switch returns -EINVAL for unknown indices).

flash_area_id_from_multi_image_slot() takes a signed int image_index while img_num is uint32_t, so the attacker controls the sign of the index as well as its magnitude: an image of 0xFFFFFFFF converts to -1 and reads all_slots[-2], off the front of the table, while large positive values read off the end (CWE-192). Either way the index multiply img * 2 is performed in int, so a wild offset yields a bus/hard fault, giving a reliable denial of service of the bootloader during recovery. For moderately out-of-range indices the read returns adjacent .rodata as a garbage flash-area id that is handed to flash_area_open(); this normally fails with MGMT_ERR_EINVAL, but if the garbage id happens to match a valid non-image partition, the subsequent erase/write can target a partition outside the image set (CWE-787). The attacker-supplied value is never echoed back, so there is no information disclosure. The fix is to reject img_num >= BOOT_IMAGE_NUMBER on the off == 0 packet, before the slot lookup. The comparison must be made on the unsigned img_num: an equivalent guard applied after the conversion to int would not reject the negative case above. __flash_area_ids_for_slot() should bounds-check its own arguments as defence in depth.
This vulnerability was reported independently twice: by NVIDIA Project Vanessa on 2026-06-22, and by Kai Phan (@kaimandalic) on 2026-07-19 as GHSA-8v33-88p6-jffj, which is closed as a duplicate of this advisory. Both original reports are reproduced in full below.

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