CVE-2026-34963 Overview
CVE-2026-34963 affects barebox, an open-source bootloader maintained by Pengutronix. Versions prior to 2026.04.0 contain multiple memory-safety defects in the EFI Portable Executable (PE) loader located at efi/loader/pe.c. An integer overflow in 32-bit arithmetic during virtual image size computation produces an undersized heap allocation. Separately, PE section loading code fails to validate that PointerToRawData plus the copied size stays within the PE file buffer. Attackers delivering a malicious EFI PE binary through TFTP, USB, SD card, or network boot can trigger heap buffer overflow or out-of-bounds reads, potentially executing code in bootloader context.
Critical Impact
Code execution at the bootloader stage compromises the system before the operating system loads, undermining Secure Boot guarantees and platform integrity.
Affected Products
- Pengutronix barebox versions prior to 2026.04.0
- EFI PE loader component (efi/loader/pe.c)
- Embedded and industrial devices using barebox for EFI boot
Discovery Timeline
- 2026-05-11 - CVE-2026-34963 published to NVD
- 2026-05-13 - Last updated in NVD database
Technical Details for CVE-2026-34963
Vulnerability Analysis
The defect resides in the EFI PE loader code path in efi/loader/pe.c. When barebox parses a PE binary, it iterates over section headers to compute the total virtual image size required for heap allocation. This arithmetic uses 32-bit integers on the VirtualAddress and section size fields. A crafted PE file with section values chosen to wrap the 32-bit accumulator produces a small allocation that the subsequent section copy loop overflows.
The second flaw appears in the section loading logic. The loader copies each section from the PE file buffer into the allocated image using the PointerToRawData field as the source offset, but does not verify that the offset plus the copy length remains within the bounds of the input buffer. A malicious PE can point PointerToRawData past the end of the file, causing the copy to read out-of-bounds heap memory.
The weakness is classified as integer overflow [CWE-190] and produces both heap buffer overflow and out-of-bounds read primitives.
Root Cause
Two missing checks combine to create the vulnerability. First, virtual image size computation performs unchecked 32-bit addition on attacker-controlled VirtualAddress and size fields. Second, section copy operations trust PointerToRawData without bounding it against the PE file buffer length.
Attack Vector
An attacker must supply a malicious EFI PE binary to the bootloader. Delivery paths include TFTP-served images during network boot, files placed on attached USB media, files on SD cards, or other boot-time storage. Exploitation requires no authentication and no user interaction beyond initiating the boot process.
No public proof-of-concept exploit code is currently available. Refer to the VulnCheck Security Advisory for technical detail.
Detection Methods for CVE-2026-34963
Indicators of Compromise
- Unexpected EFI PE binaries staged on TFTP servers, USB devices, or SD cards used for boot
- Boot logs showing PE loader errors, aborted image loads, or unexplained reboots from the EFI path
- Modifications to bootloader configuration that redirect image fetch URLs or change boot order
Detection Strategies
- Inventory devices running barebox and compare installed versions against 2026.04.0 or later
- Verify integrity of EFI PE images served by provisioning infrastructure using cryptographic hashes
- Monitor TFTP and PXE servers for anomalous file uploads or accesses tied to boot operations
Monitoring Recommendations
- Alert on physical access events involving USB or SD insertion on devices that boot via EFI
- Log and review barebox console output and serial diagnostics for PE parsing failures
- Track configuration drift in network boot infrastructure that delivers PE images
How to Mitigate CVE-2026-34963
Immediate Actions Required
- Upgrade barebox to version 2026.04.0 or later on all affected devices
- Restrict physical access to USB and SD card slots on production hardware
- Disable EFI network boot where it is not required for device operation
Patch Information
The fix is included in barebox release 2026.04.0. Source code and release notes are available at the GitHub Release v2026.04.0 page and the Barebox GitHub Repository.
Workarounds
- Limit boot sources to signed images served from trusted, access-controlled infrastructure
- Enforce verified boot or image signature validation upstream of the PE loader where the platform supports it
- Segment device management networks to prevent untrusted hosts from serving TFTP images
# Verify installed barebox version on target device
barebox --version
# Example: pin TFTP boot to a trusted server in barebox environment
edit /env/network/eth0
global.net.server=10.0.0.1
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
