CVE-2026-128091
Received
Received - Intake
Memory Leak in MCUboot TinyCrypt Backend
Vulnerability report for CVE-2026-128091, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-11-13
Last updated on: 2026-11-13
Assigner: Zephyr Project
Description
Description
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().
CVSS Scores
EPSS Scores
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Meta Information
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-226 | The product releases a resource such as memory or a file so that it can be made available for reuse, but it does not clear or "zeroize" the information contained in the resource before the product performs a critical state transition or makes the resource available for reuse by other entities. |
