CVE-2026-68432: vxlan: require CAP_NET_ADMIN in the device netns for changelink

From: Greg Kroah-Hartman <[email protected]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

vxlan: require CAP_NET_ADMIN in the device netns for changelink

A tunnel changelink() operates on at most two netns, dev_net(dev) and
the sticky underlay netns vxlan->net. They differ once the device is
created in or moved to a netns other than the one the request runs in.
The rtnl changelink path checks CAP_NET_ADMIN only against dev_net(dev),
so a caller privileged there but not in vxlan->net can rewrite a vxlan
device whose underlay lives in vxlan->net.

vxlan_changelink() validates and applies the new configuration against
vxlan->net (vxlan_config_validate(vxlan->net, ...)) and can reopen the
underlay socket in that netns, so the same reasoning as the tunnel
changelink series applies here.

Gate vxlan_changelink() with rtnl_dev_link_net_capable(), at the top of
the op before any attribute is parsed, matching ipgre_changelink() and
the rest of the "require CAP_NET_ADMIN in the device netns for
changelink" series.

Found by 0sec automated security-research tooling (https://0sec.ai).

The Linux kernel CVE team has assigned CVE-2026-68432 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 4.11 with commit 8bcdc4f3a20be949df54b67e5ae2734daabb5792 and fixed in 6.6.148 with commit b3793d7dccb192ffff29894d11824db6251acdd5
	Issue introduced in 4.11 with commit 8bcdc4f3a20be949df54b67e5ae2734daabb5792 and fixed in 6.12.101 with commit 32d10c46bfde3e9b274e9e1bd6399d0ebea8f60f
	Issue introduced in 4.11 with commit 8bcdc4f3a20be949df54b67e5ae2734daabb5792 and fixed in 6.18.42 with commit 730c7e5fea7f06e0cdf21c547222ec93234fd1d6
	Issue introduced in 4.11 with commit 8bcdc4f3a20be949df54b67e5ae2734daabb5792 and fixed in 7.1.6 with commit e8ad0d311e225939a9a6c745d6cc384c7364ec87
	Issue introduced in 4.11 with commit 8bcdc4f3a20be949df54b67e5ae2734daabb5792 and fixed in 7.2-rc5 with commit 3a61bd9637f3d929aa846e4eb3d98b48c26fcb0e

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-68432
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/net/vxlan/vxlan_core.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/b3793d7dccb192ffff29894d11824db6251acdd5
	https://git.kernel.org/stable/c/32d10c46bfde3e9b274e9e1bd6399d0ebea8f60f
	https://git.kernel.org/stable/c/730c7e5fea7f06e0cdf21c547222ec93234fd1d6
	https://git.kernel.org/stable/c/e8ad0d311e225939a9a6c745d6cc384c7364ec87
	https://git.kernel.org/stable/c/3a61bd9637f3d929aa846e4eb3d98b48c26fcb0e