CVE-2026-98023

/// Technical 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

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References