MCU-Tools MCUboot up to 2.4.x Serial Recovery boot_serial_encryption.c information disclosure

Summaryinfo

A vulnerability, which was classified as problematic, was found in MCU-Tools MCUboot up to 2.4.x. This affects the function decrypt_image_inplace/boot_image_validate_encrypted of the file boot/boot_serial/src/boot_serial_encryption.c of the component Serial Recovery. Such manipulation leads to information disclosure. This vulnerability is uniquely identified as CVE-2026-127928. Local access is required to approach this attack. No exploit exists. You should upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in MCU-Tools MCUboot up to 2.4.x. Affected by this issue is the function decrypt_image_inplace/boot_image_validate_encrypted of the file boot/boot_serial/src/boot_serial_encryption.c of the component Serial Recovery. The manipulation with an unknown input leads to a information disclosure vulnerability. Using CWE to declare the problem leads to CWE-200. The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. Impacted is confidentiality. CVE summarizes:

In MCUboot's serial-recovery encrypted-image support (boot/boot_serial/src/boot_serial_encryption.c), decrypt_image_inplace() and boot_image_validate_encrypted() each keep a stack-local struct boot_status. boot_enc_load() writes the plaintext per-image AES key into its enckey[] field. Neither function cleared this structure before returning. In addition, a decrypt failure inside the per-sector loop of decrypt_image_inplace() returned early and skipped the total_out: cleanup, which left the expanded AES key context (enc_data) on the stack as well. The error paths of boot_image_validate_encrypted() similarly skipped boot_enc_zeroize(). The affected code is built when encrypted images (MCUBOOT_ENC_IMAGES, Zephyr CONFIG_BOOT_ENCRYPT_IMAGE) are combined with serial recovery. It runs when an encrypted image is uploaded to the primary slot over the recovery protocol, and when the image list or state is queried while an encrypted image is in the secondary slot. After these functions return, the image's AES content key remains in dead stack memory. An attacker who can later read device RAM, for example through a debug port or retained RAM, can recover it. This weakens the confidentiality of image-encryption keys within the bootloader trust boundary. A recovered key exposes the plaintext of the encrypted firmware image it protects. The device's long-term private decryption key is not exposed. No remote or recovery-protocol channel that returns this memory is known, so exploitation requires a separate memory-read capability.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-127928 since 11/12/2026. The exploitation is known to be easy. The attack needs to be approached locally. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1592.

Upgrading to version 2.5.0 eliminates this vulnerability.

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Productinfo

Vendor

• MCU-Tools

Name

• MCUboot

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4

Website

• Product: https://github.com/mcu-tools/mcuboot/

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