Out-of-bounds stack write in MCUboot split-image validation with SHA-384/SHA-512 builds

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-16671
StatePUBLISHED
Assignerzephyr
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-11-13 02:18:57 UTC
Updated2026-11-13 02:18:57 UTC
Descriptionsplit_image_check() in boot/bootutil/src/loader.c declares a fixed uint8_t loader_hash[32] buffer and passes it as the out_hash out-parameter to bootutil_img_validate(). That routine copies IMAGE_HASH_SIZE bytes into out_hash (memcpy(out_hash, hash, IMAGE_HASH_SIZE) in boot/bootutil/src/image_validate.c), where IMAGE_HASH_SIZE is a compile-time constant of 64 for MCUBOOT_SHA512 or 48 for MCUBOOT_SIGN_EC384/SHA-384 (boot/bootutil/include/bootutil/crypto/sha.h). The buffer tracks SHA-256 (32 bytes) while the copy length tracks the configured algorithm, so the write overruns the buffer by 16 or 32 bytes. The overflow is only present in a non-default configuration: the legacy Mynewt split-image feature must be compiled (split_go()/split_image_check(), i.e. neither MCUBOOT_DIRECT_XIP nor MCUBOOT_RAM_LOAD), the digest must be larger than 32 bytes (MCUBOOT_SHA512 or MCUBOOT_SIGN_EC384), and MCUBOOT_SIGN_PURE must be off. split_go() is a public API with no caller inside MCUboot; it is invoked from a Mynewt application. In the default SHA-256 build there is no overflow. The over-written bytes are the one-way digest of the loader image and the overflow length is fixed at build time, so the contents are not meaningfully attacker-controlled and the size is not attacker-chosen. The realistic impact is bounded, uncontrolled corruption of the bootloader's stack on the split-boot path, manifesting as instability or failed boot in the affected configuration rather than reliable code execution. The fix is to size loader_hash to IMAGE_HASH_SIZE and pass IMAGE_HASH_SIZE as the matching seed length.

Risk And Classification

Primary CVSS: v3.1 2.9 LOW from [email protected]

CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

Problem Types: CWE-787 | CWE-787 memory-safety

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary2.9LOWCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
3.1CNACVSS2.9LOWCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Mcu-tools Mcuboot affected 2.0.0 2.5.0 semver Not specified

References

ReferenceSourceLinkTags
github.com/mcu-tools/mcuboot/commit/9fb70f00173766d73cdadd82266bd61e4ddd... [email protected] github.com
github.com/mcu-tools/mcuboot/security/advisories/GHSA-vj6q-r752-fpqv [email protected] github.com
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