External risk intelligence

Denx U-Boot ZFS Integer Overflow Leads to Code Execution

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2025-70290

This vulnerability exists in U-Boot, a bootloader used during the system startup process. It is triggered by malformed filesystem metadata, which is inherently a local or physical attack vector. It is not an internet-facing service or application reachable via common network protocols.

Integer Overflow

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

An integer overflow vulnerability in the ZFS filesystem support of Denx U-Boot could allow an attacker to execute arbitrary code or cause system crashes during the boot process by providing malformed on-disk metadata. The main concern is confirming relevance and exposure.

Flaw allows system takeover during startup.
Critical for secure boot process integrity.
Verify if your bootloader is affected.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by providing specially crafted data to the ZFS filesystem support in Denx U-Boot. This could lead to issues with memory allocation and access, potentially allowing for system crashes or the execution of arbitrary code during the device's startup sequence.

Entry condition: Malformed ZFS filesystem metadata.
Trigger point: ZFS filesystem parsing during boot.
Resulting risk: System crash or code execution.

Live Threat

Current exploitation, exposure, and threat context

An integer overflow in U-Boot's ZFS filesystem support could allow an attacker to corrupt on-disk metadata. This may lead to memory allocation issues, out-of-bounds memory access, and potentially system crashes or arbitrary code execution during the boot process when supported by the advisory.

Boot process integrity.
Malformed ZFS metadata.
System crash or code execution.

Operational Fix

Recommended remediation, mitigation, and detection steps

Real-World Ownership

This vulnerability in Denx U-Boot's ZFS filesystem support impacts the early boot process and could allow for arbitrary code execution. Ownership typically falls to the platform or embedded systems team responsible for the firmware and bootloader. The first practical step is to identify all systems running the affected U-Boot version, assess their exposure and criticality, and then coordinate remediation, which may involve vendor engagement.

Platform or embedded systems teams own remediation.
Verify ZFS usage and bootloader reachability.
Plan coordinated firmware updates.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is Denx U-Boot?

Denx U-Boot is an open-source bootloader software widely used in embedded systems and industrial devices. It serves as the initial code that runs when a device powers on, responsible for initializing hardware components and loading the operating system kernel into memory to start the platform.

What does the integer overflow in CVE-2025-70290 mean?

This vulnerability is classified as an integer overflow (CWE-190) which leads to an out-of-bounds memory access (CWE-787). In plain terms, the software performs a calculation that exceeds its expected size, causing it to miscalculate how much memory it needs. This allows the system to read or write to unauthorized memory areas, which can cause the device to crash or permit unintended code execution.

How is this vulnerability triggered?

The flaw is triggered specifically when the bootloader processes malformed ZFS filesystem metadata during the system startup sequence. It does not occur through standard network traffic or during normal operating system runtime; the corruption must be present within the ZFS data the bootloader is attempting to read.

Is this CVE-2025-70290 vulnerability reachable over the internet?

According to Halo Surface Signal, this is very unlikely. Because the issue resides in a bootloader component and requires malformed filesystem metadata to trigger, it is inherently a local or physical attack vector. It is not an internet-facing service or application reachable via common network protocols.

How should I respond if I use Denx U-Boot?

Your first step is to inventory devices to determine if they are running a version of U-Boot earlier than 2026.04 and if they utilize ZFS filesystem support. Coordinate with your platform or firmware engineering teams to verify the risk to your specific hardware and plan for official firmware updates once available from your vendor.

References

gist.github.com/c0zy1/4d9648d10a5ff07bda2771ea1298e469

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.