CVE-2026-16662: Uninitialised bootloader stack disclosed into the measured-boot attestation record via a short EXPECTED_HASH TLV in MCUboot
mcu-tools · mcuboot
Vendor fix available · Affected: mcu-tools mcuboot · Exploitation: unlikely (under 1%)
Not in CyberSIXT coverage yet: no article names this CVE. This page shows the public record.
Higher than 3% of scored CVEs
DescriptionCVE.org
boot_save_boot_status() in boot/bootutil/src/boot_record.c reads the image's EXPECTED_HASH_TLV into a stack buffer image_hash[IMAGE_HASH_SIZE] that is never zero-initialised. The TLV handler validates only the upper bound (len > sizeof(image_hash)) and then reads exactly len bytes, so a TLV shorter than IMAGE_HASH_SIZE leaves the tail of image_hash holding stale stack content. The subsequent copy into the boot record, memcpy(buf + offset, image_hash, sizeof(image_hash)), uses the fixed buffer size rather than len, so up to IMAGE_HASH_SIZE - 1 bytes of uninitialised bootloader stack are written into the measured-boot record. The defect is reachable only under MCUBOOT_MEASURED_BOOT, and only when nothing has checked the length of the hash TLV before boot_save_boot_status() reads it. bootutil_img_validate() rejects a hash TLV whose length is not exactly sizeof(hash) (boot/bootutil/src/image_validate.c:345), and primary-slot validation is on by default (Zephyr's CONFIG_BOOT_VALIDATE_SLOT0 defaults to y), so in a default build the malformed image never reaches this code. Two kinds of build let a short TLV through: Builds that use pure signatures (MCUBOOT_SIGN_PURE, Zephyr CONFIG_BOOT_SIGNATURE_TYPE_PURE). The signature covers the image itself, so the hash-TLV check in bootutil_img_validate() is compiled out, and a pure-signed image normally carries no hash TLV. A hash TLV is still allowed in the unprotected TLV area, which the signature does not cover, so a short one can be added to a correctly signed image without invalidating it. This applies with every upgrade strategy, including direct-XIP and RAM-load, and the modified image can be delivered through any path that accepts a signed image.
Affected products1
From the CVE record. A product or version that is not listed is unknown, not unaffected.
- mcu-tools · mcubootfrom 1.6.0 before 2.5.0
On the Atlas
Every published CVE is on the CyberSIXT Atlas, grouped by weakness, vendor and month.
- Exploitation
- Unlikely (under 1%). EPSS under 1%, or no score yet.
- CISA KEV
- Not listed
- Public check
- No public nuclei template
- Vendor
- mcu-tools
- Published
- November 2026
CoverageNo articles yet
No CyberSIXT article names CVE-2026-16662 yet, so there is no coverage timeline, action brief or change log for it. Everything on this page comes from the public CVE record, CISA KEV, EPSS and the nuclei template index. Search the archive or see the CVEs in the news.