{"affected":[{"defaultStatus":"unaffected","ecosystem":"https://github.com/mcu-tools/mcuboot","packageName":"mcuboot","product":"mcuboot","source":"CNA: zephyr","vendor":"mcu-tools","versions":[{"lessThan":"2.5.0","status":"affected","version":"2.0.0","versionType":"semver"}]}],"cveId":"CVE-2026-16671","cwes":["CWE-787"],"description":"split_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.\n\nThe 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.\n\nThe 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.","epss":null,"exploits":[],"kev":null,"metrics":[{"score":2.9,"severity":"low","source":"CNA: zephyr","vector":"CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L","version":"3.1"}],"modifiedAt":1794529382120,"publishedAt":1794529382120,"references":[{"source":"CNA: zephyr","tags":["patch"],"url":"https://github.com/mcu-tools/mcuboot/commit/9fb70f00173766d73cdadd82266bd61e4ddd0252"},{"source":"CNA: zephyr","tags":[],"url":"https://github.com/mcu-tools/mcuboot/security/advisories/GHSA-vj6q-r752-fpqv"}],"remediation":[{"kind":"fix","source":"CNA: zephyr","text":"The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.","url":"https://github.com/mcu-tools/mcuboot/commit/9fb70f00173766d73cdadd82266bd61e4ddd0252"}],"revision":"ce6fde791422524a5a79e4686f97268853d906c536345129b2f5fb53a4968ce4","sources":[{"modifiedAt":1794529382120,"name":"CNA: zephyr","retrievedAt":1794532181875,"url":"https://www.cve.org/CVERecord?id=CVE-2026-16671"}],"ssvc":null,"status":"published","title":"Out-of-bounds stack write in MCUboot split-image validation with SHA-384/SHA-512 builds","updatedAt":1794532181875}