# CVE-2026-127915: TLV iterator does not bound each entry against the declared TLV area in MCUboot bootutil

Status: published. Published: 2026-11-13. Updated: 2026-11-13.

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.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: zephyr) — https://github.com/mcu-tools/mcuboot/commit/90f4e7c3ebe4cf9a5eb7d981220388ffdefd6d19

## Affected products and versions

- mcu-tools / mcuboot (mcuboot): ≥ 0.9.0; < 2.5.0 (affected, semver). Source: CNA: zephyr

## Severity and prioritization

- CVSS 3.1: 2 (low); CVSS:3.1/AV:P/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L; source: CNA: zephyr

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-125

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/mcu-tools/mcuboot/commit/90f4e7c3ebe4cf9a5eb7d981220388ffdefd6d19 (CNA: zephyr; patch)

- https://github.com/mcu-tools/mcuboot/security/advisories/GHSA-4fp3-3qw2-25jv (CNA: zephyr)

## Provenance

- CNA: zephyr: https://www.cve.org/CVERecord?id=CVE-2026-127915; retrieved 2026-11-13; source updated 2026-11-13

Revision: 4649e76bd594a65fcc9c98cecc9612b4d49a98cd8b050bda5901c50081e2a889

Canonical: https://y2.dev/cve/CVE-2026-127915

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