---
id: CVE-2026-127915
title: >-
  TLV iterator does not bound each entry against the declared TLV area in
  MCUboot bootutil
summary: >-
  The MCUboot TLV iterator bootutil_tlv_iter_next() in boot/bootutil/src/tlv.c
  walks image trailer TLVs with a single loop guard (it->tlv_off < it->tlv_end)
  and advances by sizeof(struct image_tlv) + tlv.it_len using the
  attacker-controlle…
severity: low
cvss: 2
cvssVector: 'CVSS:3.1/AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L'
cvssSource: cna
cwe:
  - CWE-125
vendor: mcu-tools
product: mcuboot
affected:
  - mcuboot >= 0.9.0 < 2.5.0
published: '2026-11-13'
updated: '2026-11-13'
sourceUpdated: '2026-11-13T00:23:07.449Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-127915'
references:
  - url: >-
      https://github.com/mcu-tools/mcuboot/commit/90f4e7c3ebe4cf9a5eb7d981220388ffdefd6d19
    label: Fix commit
  - url: >-
      https://github.com/mcu-tools/mcuboot/security/advisories/GHSA-4fp3-3qw2-25jv
    label: GHSA-4fp3-3qw2-25jv
tags:
  - cve.org
ingestedAt: '2026-11-13T01:19:02.071Z'
---

## Overview

The MCUboot TLV iterator bootutil_tlv_iter_next() in boot/bootutil/src/tlv.c walks image trailer TLVs with a single loop guard (it->tlv_off < it->tlv_end) and advances by sizeof(struct image_tlv) + tlv.it_len using the attacker-controlled it_len field, without validating that the entry's header or payload stays within it->tlv_end. As a result the 4-byte header read can extend up to 3 bytes past the declared TLV area, and the returned (off, len) can describe a payload that runs past it.

The path is pre-authentication: TLVs are parsed during bootutil_img_validate() before the signature is verified, and a crafted image can be presented through DFU / serial-recovery / OTA. However the impact is contained by surrounding guards: bootutil_img_validate() first rejects a TLV area larger than bootutil_max_image_size(), the default LOAD_IMAGE_DATA sink is flash_area_read() which bounds-checks against the flash partition and fails an out-of-partition read, and every payload consumer (EXPECTED_HASH_TLV, EXPECTED_KEY_TLV, EXPECTED_SIG_TLV, IMAGE_TLV_SEC_CNT) clamps len against a fixed buffer before copying.

The residual effect in a default flash build is therefore an out-of-region read confined to the attacker's own slot partition whose result is never observable, yielding at worst a clean validation failure rather than memory corruption or information disclosure. A genuine (though still bounded) out-of-bounds read remains under the non-default MCUBOOT_RAM_LOAD configuration, where LOAD_IMAGE_DATA is an unchecked memcpy. The fix is to validate each entry's header and payload against it->tlv_end inside the iterator.

## Affected

- `mcuboot >= 0.9.0 < 2.5.0`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.