CVE-2025-70290 in U-Boot
Summary
by MITRE • 08/26/2026
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.
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Analysis
by VulDB Data Team • 08/26/2026
The discovery of an integer overflow vulnerability within the Denx U-Boot firmware prior to version 2026.04 represents a critical security flaw with significant implications for system integrity and availability. This specific weakness resides in the ZFS filesystem support module, which is responsible for parsing on-disk metadata structures during the boot sequence. The root cause of this vulnerability is an improper handling of integer values when calculating buffer sizes or offsets based on data extracted from disk sectors. When a malformed or maliciously crafted ZFS superblock or other metadata structure is encountered, the arithmetic operations used to determine memory requirements fail to account for potential overflow conditions. This failure leads to the allocation of a significantly smaller memory buffer than what is actually required by the subsequent parsing logic.
The operational impact of this flaw stems directly from the resulting out-of-bounds memory access. Because the allocated buffer is insufficient, any attempt to read or write data beyond its boundaries will corrupt adjacent memory regions. In the context of U-Boot, which operates at a low level in system initialization, such corruption can easily overwrite critical control flow data, function pointers, or stack variables. This scenario creates two primary attack vectors: denial of service and arbitrary code execution. A simple malformed metadata structure can cause an immediate crash during boot, effectively bricking the device if recovery mechanisms are not present. More dangerously, a carefully crafted payload could allow an attacker to execute arbitrary instructions within the U-Boot environment. Since U-Boot often runs with high privileges before handing control over to the operating system kernel, successful exploitation could lead to full system compromise, including the ability to modify boot parameters, inject malicious kernels, or persist malware in non-volatile storage.
From a classification perspective, this vulnerability aligns closely with CWE-190, which defines integer overflow or wraparound errors that can lead to subsequent memory corruption issues. The specific mechanism of allocating insufficient memory due to arithmetic miscalculation is also characteristic of CWE-787, an out-of-bounds write vulnerability. Furthermore, the exploitation path leverages the initial boot phase to gain unauthorized access and potentially modify system configuration, which maps to MITRE ATT&CK techniques such as T1531, Accessing Cloud Storage for Initial Payload Delivery if cloud-based firmware updates are involved, or more directly T1059 Command and Scripting Interpreter if U-Boot scripts are manipulated. The attack vector is typically local physical access or compromised update mechanisms, making it a high-risk issue for embedded systems where physical security might be assumed but not guaranteed.
Mitigation strategies must focus on both immediate patching and long-term architectural improvements. The primary remediation is to upgrade Denx U-Boot to version 2026.04 or later, where the integer overflow in ZFS metadata parsing has been addressed through rigorous input validation and safe arithmetic checks. Developers should implement explicit bounds checking before any memory allocation based on external data inputs. Additionally, enabling compiler security features such as stack canaries, Address Sanitizers during development builds, and Full Relocation Read-Only Executables (FRRX) can help mitigate the impact of exploitation attempts by making it harder to hijack control flow or execute injected code. For system integrators, enforcing strict verification of firmware images using cryptographic signatures before flashing them into devices is essential to prevent the introduction of maliciously crafted ZFS metadata from untrusted sources. Regular security audits focusing on low-level memory management functions in bootloader components are also recommended to identify similar vulnerabilities across other filesystem drivers supported by U-Boot.