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VulnerabilityAwaiting classification

CVE-2026-64410

CRITICAL · 9.8 CVSS v3.1 Published 2026-07-25
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click 4 weeks old

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

The Linux kernel's netfilter flowtable implementation incorrectly attempts hardware offload for IPIP (IP-in-IP) tunnels even though no network drivers support this feature. The vulnerability allows hardware offload work to be enqueued and retried indefinitely for unsupported tunnel configurations, potentially causing resource exhaustion or unexpected behavior.

MitigationApply the kernel patch that adds early detection and rejection of IPIP tunnel hardware offload attempts, preventing unsupported offload configuration from being queued or retried.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check kernel version
    Run 'uname -r' to get the kernel version and compare it against the affected version range for this CVE (typically kernel versions lacking the IPIP flowtable offload fix)
    Affected if The kernel version is within the range that lacks the fix for CVE-2026-64410
  2. Verify netfilter flowtable is active
    Run 'conntrack -L' or check /proc/net/netfilter/nf_conntrack* files; also check if 'flowtable' entries exist in iptables -t filter -L or nft list ruleset
    Affected if Netfilter flowtable is actively processing connections, enabling the attack surface
  3. Check for IPIP tunnel configuration
    Run 'ip tunnel list' or check 'ip link show' for tunnel interfaces with 'ipip' type; also examine /etc/network/interfaces or systemd network configs for IPIP tunnel definitions
    Affected if IPIP tunnels are configured and active on the system
  4. Verify hardware offload is enabled for flowtable
    Check iptables/nftables flowtable configuration for 'hw_offload' flag: 'iptables -t filter -L -v' or 'nft list ruleset | grep -i flowtable'; also check 'ethtool -k <interface>' for hw offload features
    Affected if Hardware offload is enabled on the flowtable (hw_offload flag set) and network interfaces support offload
  5. Check for NF_FLOW_HW flag usage
    Inspect kernel logs (dmesg, journalctl -k) for flowtable-related messages; examine /sys/module/nf_conntrack/parameters for flow_hw or similar flags; check flowtable rule configurations for NF_FLOW_HW flag presence
    Affected if The NF_FLOW_HW flag is being used, which enables retry attempts for hardware offload that could trigger the undefined behavior

The system is affected if it runs a vulnerable kernel version, has netfilter flowtable enabled with hardware offload, and uses IPIP tunnels that could trigger unsupported hardware offload attempts.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the kernel patch that adds early detection and rejection of IPIP tunnel hardware offload attempts, preventing unsupported offload configuration from being queued or retried.

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA2.0 h
14.0 hours of engineering $2,380
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-64410 in production — separate from our analysis above.

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