CVE-2026-98023

Received Received - Intake

VXLAN FDB Dynamic Entry Rejection in Linux Kernel

Publication date: 2026-09-25

Last updated on: 2026-10-03

Assigner: kernel.org

Description

In the Linux kernel, the following vulnerability has been resolved: vxlan: reject dynamic fdb entries that reference a nexthop id The commit cited in the Fixes tag allowed VXLAN FDB entries to point to FDB nexthops so that overlay traffic could be load balanced across multiple VTEPs. Such entries can only be configured from user space, cannot be learned and cannot roam. They only make sense with a user space control plane such as E-VPN where data plane learning is disabled. Despite that, the VXLAN driver does not currently prevent such entries from being configured with the "dynamic" flag. The per-nexthop FDB list is only protected by the per-device hash lock, which is not sufficient when two VXLAN devices point to the same FDB nexthop and therefore share the list. Aging runs in softirq context without RTNL, so an entry deleted by one device can race with an addition or deletion from the other, leading to list corruption: list_del corruption. next->prev should be ffff8881069d9548, but was dead000000000122. (next=ffff8881069d9448) WARNING: CPU: 0 PID: 90 at lib/list_debug.c:65 __list_del_entry_valid_or_report+0x1aa/0x210 ... vxlan_fdb_destroy+0x5b8/0xad0 vxlan_cleanup+0x328/0x450 call_timer_fn+0x2a/0x1c0 run_timer_softirq+0x18c/0x210 BUG: KASAN: slab-use-after-free in vxlan_fdb_destroy Fix this by rejecting the bogus configuration of dynamic FDB entries that point to FDB nexthops, both when created and when an existing entry is updated. As such, the per-nexthop FDB list is only ever mutated under the RTNL lock. Add test cases to make sure that this does not regress in the future.

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Meta Information

Published

2026-09-25

Last Modified

2026-10-03

Generated

2026-10-15

AI Q&A

2026-09-25

EPSS Evaluated

2026-10-14

NVD

CVE-2026-98023

EUVD

EUVD-2026-86676

Affected Vendors & Products

Vendor	Product	Version / Range
linux	linux_kernel	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-UNKNOWN

Attack-Flow Graph

Executive Summary

This vulnerability in the Linux kernel involves VXLAN FDB entries incorrectly allowing dynamic configuration with a nexthop ID. Normally, such entries should only be set via user space with a control plane like E-VPN. The issue arises because the VXLAN driver does not block setting the 'dynamic' flag, leading to list corruption when two VXLAN devices share the same nexthop. This causes race conditions during aging in softirq context, resulting in kernel errors like list_del corruption and slab-use-after-free.

Detection Guidance

This vulnerability is specific to the Linux kernel's VXLAN implementation and may not have direct detection commands. However, you can check for kernel logs indicating list corruption or crashes related to VXLAN operations. Monitor logs for messages like 'list_del corruption' or 'slab-use-after-free' in vxlan_fdb_destroy. Use 'dmesg | grep -i vxlan' or 'journalctl -k | grep -i vxlan' to inspect kernel logs.

Impact Analysis

This vulnerability can cause kernel crashes, data corruption, or system instability due to list corruption in the VXLAN FDB. It may lead to denial-of-service conditions if the kernel panics or becomes unresponsive. Systems relying on VXLAN for network virtualization could experience connectivity issues or unexpected behavior.

Compliance Impact

This vulnerability does not directly affect compliance with standards like GDPR or HIPAA as it is a Linux kernel issue related to VXLAN FDB entry handling. Compliance impacts would depend on system configuration and use case rather than the vulnerability itself.

Mitigation Strategies

Apply the kernel patch that fixes this issue by rejecting dynamic FDB entries pointing to FDB nexthops. Update your Linux kernel to a version that includes the fix. If immediate patching is not possible, disable dynamic FDB entries for VXLAN devices or restrict user space control plane configurations that allow such entries.

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