CVE-2026-128091: AES key schedule not cleared by the TinyCrypt AES-CTR backend in MCUboot bootutil
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 0% of scored CVEs
DescriptionCVE.org
When MCUboot is built with the TinyCrypt crypto backend (MCUBOOT_USE_TINYCRYPT), bootutil_aes_ctr_drop() in boot/bootutil/include/bootutil/crypto/aes_ctr_tinycrypt.h was an empty stub. The AES-CTR context for this backend is the fully expanded AES-128 key schedule (struct tc_aes_key_sched_struct). Generic code relies on this hook to release and clear key state, so with TinyCrypt nothing was cleared. The mbedTLS and PSA backends do free or destroy their key state here. As a result, boot_state_clear(), which boot_go() calls before handing off to the application, left the image's AES content-encryption key schedule in the static boot_data state. This is the case after an encrypted upgrade in single-image builds, where boot_enc_zeroize() is not called. boot_decrypt_key() likewise left the ECIES-derived key-encryption key schedule on the stack. The affected build uses MCUBOOT_ENC_IMAGES with TinyCrypt, which is the default ECDSA and Ed25519 backend in the Zephyr port. The first AES-128 round key equals the cipher key, so anyone who can read the leftover bootloader RAM after boot can recover the image content key and decrypt that encrypted image. That includes a physical attacker with debug or RAM access, or code later running on the device. This weakens image-encryption key confidentiality (and so the confidentiality of the encrypted image's plaintext). The device's long-term private decryption key is not exposed, and image authenticity is not affected. The fix wipes the context with bootutil_wipe_memory().
Affected products1
From the CVE record. A product or version that is not listed is unknown, not unaffected.
- mcu-tools · mcubootfrom 1.3.0 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-2026-128091 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.