Das U-Boot and Barebox FIT Signature Verification Bypass Vulnerability Allowing Image Replacement

A vulnerability exists in Das U-Boot versions through 2025.10 and in Barebox versions 2016.03.0 prior to 2026.04, allowing a bypass of the Flat Image Tree (FIT) signature verification. This issue arises because the 'hashed-nodes' property, which indicates which nodes were included in the signature hash, is not properly validated. An attacker with local or physical access can exploit this by modifying the 'hashed-nodes' property to deceive the bootloader into loading unverified images. The vulnerability can lead to unauthorized code execution, potentially compromising the kernel and, depending on the bootloader and platform, other system components such as the hypervisor or trusted services.

Impact

Exploitation of this vulnerability can result in unauthorized code execution at the privilege level of the original payload. In the case of Barebox on 32-bit ARM, all privilege levels of the CPU can be compromised. For U-Boot, the impact varies by system configuration but can also lead to a compromise of all privilege levels on some platforms.

Reproduction

To reproduce this vulnerability, create a FIT image and manipulate the 'hashed-nodes' property to exclude certain nodes. Then, upload this modified image to a device running an affected version of U-Boot or Barebox. The bootloader will be tricked into booting images that have not been properly verified, allowing for the execution of unauthorized code.

Remediation

Users can update to Barebox versions 2026.03.1 or 2025.09.3, or to U-Boot versions 2026.07-rc2 or 2026.04-rc4, which include patches for this vulnerability.