External risk intelligence

Linux Kernel netfilter Flowtable IPIP Tunnel Hardware Offload Not Supported.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-64410

This vulnerability resides within the Linux kernel's netfilter flowtable hardware offload subsystem. It involves low-level network processing logic concerning tunnel offloading. Such internal kernel mechanisms are not directly exposed to the public internet and require deep, authenticated, or local access to trigger, making public-facing exploitation extremely unlikely.

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

This CVE addresses a limitation in the Linux kernel's netfilter component where hardware offload for IPIP tunnels is not yet supported, leading to the system not leveraging hardware acceleration for this specific network traffic. While the vulnerability has been resolved, the primary concern is to confirm if this specific functionality was in use and potentially exposed.

Kernel networking feature is not supported.
Confirm if unsupported tunnel offload was in use.
Verify if this internal limitation impacts your systems.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending specially crafted network traffic that attempts to utilize the IPIP tunnel hardware offload feature in the Linux kernel. This interaction targets the netfilter subsystem. When hardware offload is not supported for IPIP tunnels, the system may mishandle these requests, potentially leading to a denial-of-service condition or other system instability.

Network access required for interaction.
Triggered by unsupported tunnel offload requests.
Potential for denial-of-service.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could impact the stability of network traffic processing when hardware offload for IPIP tunnels is attempted on unsupported systems. The system may enqueue offload work that is subsequently ignored.

System stability.
Unsupported hardware offload scenarios.
Unpredictable network behavior.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability resides in the Linux kernel's netfilter component, specifically related to IPIP tunnel hardware offload. Responsibility for addressing this likely falls to infrastructure or platform teams managing the kernel, in coordination with network and security teams to assess exposure and impact. The first practical step is to identify all systems running the affected kernel version, determine if the affected functionality is enabled and exposed, and confirm ownership for remediation planning.

Kernel infrastructure teams own resolution.
Verify affected kernel and enabled features.
Plan remediation based on exposure risk.

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 the Linux kernel netfilter flowtable component?

The Linux kernel netfilter is a powerful framework that manages network traffic filtering and packet manipulation. The flowtable component acts as a high-speed routing engine that offloads packet processing to network hardware to increase throughput. It is commonly used in routers, firewalls, and data centers to handle heavy traffic loads efficiently by bypassing slower software-based processing for established network connections.

What does CVE-2026-64410 mean for system security?

This CVE addresses a logic flaw where the kernel fails to properly handle hardware offload requests for IPIP tunnels. Because the necessary support for this specific tunnel type is missing, the system may mishandle incoming traffic packets. This mismatch in processing logic can cause the system to crash or stop responding, which is technically classified as a denial-of-service weakness, as the kernel cannot gracefully reject the unsupported offload attempt.

How is this netfilter vulnerability triggered?

The vulnerability is triggered when a system receives specially crafted network traffic that specifically attempts to use IPIP tunnel hardware acceleration. If the hardware does not support this tunnel type, the kernel's attempt to process the offload can lead to instability. Simply using IPIP tunnels on a system without hardware offload enabled does not trigger this issue, as the bug is specific to the hardware offload logic path.

Is my network infrastructure at risk from CVE-2026-64410?

Halo Surface Signal indicates that exploitation is very unlikely because this vulnerability exists within internal, low-level kernel mechanisms for hardware acceleration. These subsystems are generally not exposed to the public internet. Systems are most relevant if they use complex network hardware offloading and run the specific kernel versions where this logic was missing, though direct remote triggers are generally constrained by kernel-level protections.

How should I respond to this kernel update?

Start by identifying systems in your environment that utilize Linux kernel network offloading features. Once identified, coordinate with your infrastructure or platform engineering teams to verify if your specific kernel version includes the fix. The goal is to ensure that the kernel correctly identifies unsupported offload requests rather than attempting to process them. Prioritize systems where custom or high-performance networking configurations rely heavily on netfilter flowtables.

References

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.