CVE-2026-64410 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
netfilter: flowtable: IPIP tunnel hardware offload is not yet support
No driver supports for IPIP tunnels yet, give up early on setting up the hardware offload for this scenario.
This patch adds a stub that can be enhanced to add more configuration that are currently not supported. As of now, the offload work is enqueued to the worker, then ignored if the hardware offload configuration is not supported.
Check the NF_FLOW_HW flag to know if this entry was already tried once to be offloaded so this is not retried on refresh when unsupported. Move NF_FLOW_HW flag check to nf_flow_offload_add(). If this NF_FLOW_HW flag is unset the _del and _stats variants are never called.
This can be updated later on to skip hardware offload work to be queued in case hardware offload does not support it.
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Analysis
by VulDB Data Team • 07/26/2026
The vulnerability identified in the Linux kernel's netfilter subsystem relates to incomplete hardware offload support for IPIP (IP in IP) tunnels within flowtable operations. This represents a design limitation where the kernel's network filtering infrastructure cannot properly handle hardware acceleration for IPIP tunnel traffic, creating a gap in performance optimization capabilities. The issue manifests when the system attempts to configure hardware offload for IPIP tunnel flows, but no drivers currently support this specific tunnel type, resulting in a graceful degradation rather than a complete failure.
The technical flaw stems from the absence of proper driver support for IPIP tunnel hardware offload operations within the netfilter flowtable framework. When the kernel encounters an IPIP tunnel flow that should be hardware offloaded, it enqueues the offload work to a worker thread but subsequently ignores this configuration because the necessary driver support is missing. This behavior creates unnecessary processing overhead as the system performs work that ultimately yields no benefit due to the lack of underlying hardware capability. The implementation follows a defensive programming approach by checking for hardware support before attempting offload operations, though this check occurs too late in the process.
From an operational perspective, this vulnerability affects network performance in environments where IPIP tunnels are utilized extensively, particularly in virtualized or containerized deployments where such tunneling mechanisms are common. The impact is primarily performance-related rather than security-critical, as the system continues to function correctly but without hardware acceleration benefits for IPIP traffic. Network administrators may observe suboptimal packet processing performance when dealing with large volumes of IPIP tunnel traffic, as the kernel must rely on software-based processing instead of leveraging specialized hardware capabilities.
The mitigation strategy involves implementing early detection and graceful handling of unsupported hardware offload scenarios. The patch introduces a stub mechanism that can be extended to support additional configurations currently not available, providing a foundation for future enhancement while maintaining backward compatibility. The solution incorporates flag-based tracking through the NF_FLOW_HW flag to prevent redundant processing attempts, specifically ensuring that _del and _stats variants are never called when hardware offload is unsupported. This approach aligns with common network security practices where systems must handle incomplete feature support gracefully while maintaining operational integrity.
The vulnerability can be classified under CWE-20: Improper Input Validation, as it relates to insufficient validation of hardware capability support before attempting configuration operations. From an ATT&CK framework perspective, this represents a limitation in system optimization capabilities rather than a direct attack surface, though it could potentially impact network performance in denial-of-service scenarios involving high-volume tunnel traffic. The solution demonstrates proper defensive programming techniques by implementing early exit conditions and maintaining consistent state management through flag-based tracking mechanisms.
This issue highlights the complexity of modern kernel networking subsystems where hardware acceleration features must be carefully coordinated with driver capabilities. The patch's approach of adding stub support rather than complete removal ensures that future enhancements can build upon existing infrastructure, following established patterns for feature development in kernel space. The worker thread queuing mechanism maintains system responsiveness while avoiding unnecessary processing overhead, though the ultimate resolution requires either driver enhancement or architectural changes to properly support IPIP tunnel hardware offload scenarios.
The implementation reflects industry best practices for handling incomplete feature support in complex systems, where graceful degradation is preferred over complete failure modes. By checking the NF_FLOW_HW flag within nf_flow_offload_add() and preventing retries on refresh operations, the system avoids redundant processing while maintaining proper state tracking. This approach ensures that network performance remains optimal for supported configurations while gracefully handling unsupported scenarios, demonstrating sound engineering principles for kernel-level networking components that must operate reliably across diverse hardware environments and use cases.