Attack Chain

1. Attacker crafts a malicious EFI PE binary containing a crafted PE header and sections.
2. The attacker provides the malicious EFI PE binary to the target system through a bootable medium (TFTP, USB, SD card, or network boot).
3. The barebox bootloader initiates the EFI PE loader to process the provided binary.
4. During virtual image size computation, the 32-bit arithmetic on section VirtualAddress and size values causes an integer overflow, leading to an undersized heap allocation.
5. The PE section loading logic fails to validate that the sum of PointerToRawData and the copied size remains within the bounds of the PE file buffer.
6. The vulnerable memcpy function writes data beyond the allocated heap buffer, resulting in a heap buffer overflow.
7. Alternatively, the vulnerable logic attempts to read data from outside the bounds of the PE file, resulting in an out-of-bounds read from heap memory.
8. By carefully crafting the malicious PE binary, the attacker can overwrite critical data structures in memory or inject and execute arbitrary code within the bootloader context.

Impact

Successful exploitation of CVE-2026-34963 can lead to arbitrary code execution within the barebox bootloader environment. This allows an attacker to gain complete control over the affected system during the boot process. This can lead to data theft, system compromise, or the installation of persistent malware. The number of affected systems depends on the deployment of vulnerable barebox versions.

Recommendation

• Upgrade to barebox version 2026.04.0 or later to remediate CVE-2026-34963.
• Monitor boot processes for attempts to load EFI PE binaries from untrusted sources (TFTP, USB, SD card, network boot), potentially correlating with network connection logs to TFTP servers.
• Deploy the Sigma rule “Detect Suspicious EFI PE Binary Load” to detect potential exploitation attempts by monitoring process execution.