Executive brief
barebox is a bootloader used in embedded systems to load and verify the operating system kernel. A vulnerability in its FIT (Flat Image Tree) signature verification allows an attacker with physical or local storage access to modify boot images without detection, potentially compromising all privilege levels including the kernel, hypervisor, and trusted services. This breaks the secure boot chain and enables arbitrary code execution at system startup.
Technical details
The vulnerability is a signature verification bypass in the FIT container format. The mkimage(1) tool signs a FIT by hashing selected nodes and stores a list of hashed nodes in the "hashed-nodes" property; however, this property itself is not included in the signature hash. An attacker can modify hashed-nodes to reference different images than those actually signed, causing the bootloader to verify and boot attacker-controlled images instead of the legitimate ones. The attack requires physical or local access to read/write the FIT on storage. Affected versions are 2016.03.0 through 2026.02.0 (patched in 2026.03.1 and backported to 2025.09.3). The fix reconstructs the hashed nodes list from the FIT configuration rather than trusting the hashed-nodes property.
Affected products
- barebox barebox 2016.03.0 to before 2026.03.1 (also affects 2025.09.x before 2025.09.3)
Timeline
- 2026-03-20: disclosed: Public disclosure of CVE-2026-33243
- 2026-03-17: patched: Patch included in barebox v2026.03.1 and v2025.09.3
- 2026-03-02: other: Issue reported privately by Apple Security Engineering and Architecture (SEAR)