Description

An issue was discovered in Denx U-Boot before 2026.04. An integer overflow vulnerability in the ZFS filesystem support can be triggered by malformed on-disk metadata. The issue may result in incorrect memory allocation followed by out-of-bounds memory access, potentially leading to a crash or arbitrary code execution during the boot process.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "9.8",
  "pubDate": "2026-08-26T20:16:59.550Z",
  "pubdate": "2026-08-26T20:16:59.550Z",
  "executiveSummary": "An integer overflow vulnerability exists within the ZFS filesystem implementation of Denx U-Boot, affecting versions prior to 2026.04.\nThe vulnerability originates from the improper handling of malformed on-disk metadata during filesystem parsing.\nAn attacker capable of providing a specially crafted ZFS-formatted disk or partition can trigger this overflow, leading to incorrect memory allocation calculations.\nSuccessful exploitation results in out-of-bounds memory access, which may manifest as a system crash or enable arbitrary code execution during the boot sequence.\nBecause U-Boot operates in the early stages of the boot process, successful exploitation poses a critical risk to the integrity of the platform, potentially bypassing secure boot chains or facilitating persistent firmware-level compromise.\nNo specific authentication is required if the attacker can present the malicious medium to the device; the threat is primarily relevant for hardware environments where external storage input is enabled.",
  "technicalDetails": "The vulnerability resides within the ZFS filesystem driver component of the U-Boot bootloader. It is fundamentally an integer overflow flaw triggered by the parsing of maliciously crafted ZFS metadata structures stored on-disk.\nWhen U-Boot attempts to mount or access a ZFS partition, the driver processes various metadata headers and pointers to resolve file locations and structures. The vulnerability occurs when these metadata fields contain values that, when subjected to arithmetic operations (typically for memory allocation size calculations), exceed the maximum capacity of the integer type used by the host architecture.\nBecause the resulting overflowed value is significantly smaller than the actual required buffer size, the allocator requests an insufficient amount of heap space. Subsequent write operations based on the original, larger metadata lengths result in a heap-based out-of-bounds memory access.\nThe attack flow follows a sequential process: First, the attacker prepares a malicious image containing a ZFS partition with corrupted or crafted metadata fields designed to force an integer wrap-around during calculation. Second, the attacker presents this medium to a target device configured to boot or load data from external storage. Third, U-Boot initiates the ZFS driver to read the filesystem, triggering the vulnerable arithmetic operation.\nAs a result of the incorrect memory allocation, subsequent data copy operations perform out-of-bounds writes. This provides an attacker with the primitive required to overwrite critical memory regions, such as function pointers or return addresses stored in the stack or heap.\nBy controlling the data written out-of-bounds, an attacker can hijack the control flow of the U-Boot execution environment. Given that U-Boot operates in a high-privilege execution state, this vulnerability allows for the execution of arbitrary code with full access to the underlying hardware before the operating system is even loaded. This bypasses typical user-mode security controls and persists until the system is fully re-initialized or power-cycled.\nThe vulnerability affects Denx U-Boot versions prior to 2026.04 and requires no authentication, provided the hardware platform allows for the ingestion of external ZFS-formatted media."
}