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

vxlan: mdb: Fix use-after-free in vxlan_mdb_flush()

vxlan_mdb_flush() iterates over the MDB entries using
hlist_for_each_entry_safe(), which only tolerates the removal of the
current entry. Contrary to the comment above the loop, the removal of an
entry can trigger the removal of another entry.

Flushing the remotes of a (*, G) entry also removes the (S, G) entries
that were created for its source list, once they are left without
remotes:

vxlan_mdb_remotes_flush()
-> vxlan_mdb_remote_del()
-> vxlan_mdb_remote_srcs_del()
-> vxlan_mdb_remote_src_del()
-> vxlan_mdb_remote_src_fwd_del()
-> __vxlan_mdb_del()
-> vxlan_mdb_entry_put()

Such an entry can be located after the (*, G) entry in the list, as
vxlan_mdb_entry_get() returns an existing entry without moving it to the
head of the list. This order is obtained by adding the (S, G) entry
before the (*, G) entry, the latter with NLM_F_REPLACE, as the addition
of the source otherwise fails with -EEXIST. The (S, G) entry is then the
entry saved by hlist_for_each_entry_safe() and it is freed while the
(*, G) entry is processed. The next iteration calls hlist_del() on it
again, writing LIST_POISON1 to LIST_POISON2 [1].

Besides device deletion, the flush is also reachable from RTM_DELMDB
with NLM_F_BULK.

Fix by re-reading the next entry after the remotes were flushed. The
current entry cannot be removed by this flush, as source lists can only
be configured on (*, G) entries and the removed entries are (S, G)
entries. It is therefore still linked and its next pointer reflects the
removals.

[1]
BUG: KASAN: wild-memory-access in vxlan_mdb_entry_put.part.0+0x328/0x588
Write of size 8 at addr dead000000000122 by task ip/327

CPU: 3 UID: 1000 PID: 327 Comm: ip Not tainted 7.2.0-rc7 #2 PREEMPT
Call trace:
vxlan_mdb_entry_put.part.0+0x328/0x588
vxlan_mdb_flush+0x1d8/0x25c
vxlan_mdb_fini+0x8c/0x100
vxlan_uninit+0x1c/0x7c
unregister_netdevice_many_notify+0x954/0xd4c
rtnl_dellink+0x210/0x530
rtnetlink_rcv_msg+0x434/0x4d0
netlink_rcv_skb+0xc4/0x204
rtnetlink_rcv+0x18/0x24
netlink_unicast+0x4b8/0x548
netlink_sendmsg+0x29c/0x560
____sys_sendmsg+0x390/0x3ec
___sys_sendmsg+0x114/0x188
__sys_sendmsg+0xf0/0x178
__arm64_sys_sendmsg+0x48/0x60
invoke_syscall.constprop.0+0x58/0x180
el0_svc_common.constprop.0+0x74/0x140
do_el0_svc+0x30/0x40
el0_svc+0x38/0x98
el0t_64_sync_handler+0xa0/0xe4
el0t_64_sync+0x198/0x19c
Published: 2026-09-24
Score: 7.8 High
EPSS: < 1% Very Low
KEV: No
Impact: Use‑after‑free leading to kernel crash and denial of service
Action: Patch Kernel
AI Analysis

Impact

The vulnerability is a use‑after‑free issue in the vxlan_mdb_flush() routine of the Linux kernel. During a flush, an entry is freed while still referenced by the iteration loop, causing a KASAN warning and possible kernel crash. This flaw could trigger denial of service and is classified as CWE‑416.

Affected Systems

All Linux kernel builds that include the vxlan module and have not applied the commit that fixes the issue, such as any distribution kernel built before the patch with commit 3e6b705bc162fc7257645725a7d2cf6c71250318.

Risk and Exploitability

The CVSS score is 7.8, indicating a high severity level. EPSS is not available, and the vulnerability is not listed in the CISA KEV catalog. Based on the code paths described, an attacker would need privileged access to configure or delete VXLAN interfaces, or to send netlink messages such as RTM_DELMDB to trigger the flush. The exploit would cause the kernel to crash, leading to loss of availability for any affected services.

Generated by OpenCVE AI on September 25, 2026 at 10:26 UTC.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Update the kernel to a version that includes commit 3e6b705bc162fc7257645725a7d2cf6c71250318 or a later release that contains the fix.
  • Reboot the system or reload the kernel and vxlan module to ensure the new code is active.
  • If a kernel update cannot be applied immediately, disable or remove all VXLAN interfaces until the patch is installed.

Generated by OpenCVE AI on September 25, 2026 at 10:26 UTC.

Tracking

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Advisories
Source ID Title
Debian DLA Debian DLA DLA-4817-1 linux-6.12 security update
Debian DSA Debian DSA DSA-6528-1 linux security update
History

Fri, 25 Sep 2026 10:45:00 +0000

Type Values Removed Values Added
Weaknesses CWE-416

Fri, 25 Sep 2026 05:15:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'}

Thu, 24 Sep 2026 16:00:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: vxlan: mdb: Fix use-after-free in vxlan_mdb_flush() vxlan_mdb_flush() iterates over the MDB entries using hlist_for_each_entry_safe(), which only tolerates the removal of the current entry. Contrary to the comment above the loop, the removal of an entry can trigger the removal of another entry. Flushing the remotes of a (*, G) entry also removes the (S, G) entries that were created for its source list, once they are left without remotes: vxlan_mdb_remotes_flush() -> vxlan_mdb_remote_del() -> vxlan_mdb_remote_srcs_del() -> vxlan_mdb_remote_src_del() -> vxlan_mdb_remote_src_fwd_del() -> __vxlan_mdb_del() -> vxlan_mdb_entry_put() Such an entry can be located after the (*, G) entry in the list, as vxlan_mdb_entry_get() returns an existing entry without moving it to the head of the list. This order is obtained by adding the (S, G) entry before the (*, G) entry, the latter with NLM_F_REPLACE, as the addition of the source otherwise fails with -EEXIST. The (S, G) entry is then the entry saved by hlist_for_each_entry_safe() and it is freed while the (*, G) entry is processed. The next iteration calls hlist_del() on it again, writing LIST_POISON1 to LIST_POISON2 [1]. Besides device deletion, the flush is also reachable from RTM_DELMDB with NLM_F_BULK. Fix by re-reading the next entry after the remotes were flushed. The current entry cannot be removed by this flush, as source lists can only be configured on (*, G) entries and the removed entries are (S, G) entries. It is therefore still linked and its next pointer reflects the removals. [1] BUG: KASAN: wild-memory-access in vxlan_mdb_entry_put.part.0+0x328/0x588 Write of size 8 at addr dead000000000122 by task ip/327 CPU: 3 UID: 1000 PID: 327 Comm: ip Not tainted 7.2.0-rc7 #2 PREEMPT Call trace: vxlan_mdb_entry_put.part.0+0x328/0x588 vxlan_mdb_flush+0x1d8/0x25c vxlan_mdb_fini+0x8c/0x100 vxlan_uninit+0x1c/0x7c unregister_netdevice_many_notify+0x954/0xd4c rtnl_dellink+0x210/0x530 rtnetlink_rcv_msg+0x434/0x4d0 netlink_rcv_skb+0xc4/0x204 rtnetlink_rcv+0x18/0x24 netlink_unicast+0x4b8/0x548 netlink_sendmsg+0x29c/0x560 ____sys_sendmsg+0x390/0x3ec ___sys_sendmsg+0x114/0x188 __sys_sendmsg+0xf0/0x178 __arm64_sys_sendmsg+0x48/0x60 invoke_syscall.constprop.0+0x58/0x180 el0_svc_common.constprop.0+0x74/0x140 do_el0_svc+0x30/0x40 el0_svc+0x38/0x98 el0t_64_sync_handler+0xa0/0xe4 el0t_64_sync+0x198/0x19c
Title vxlan: mdb: Fix use-after-free in vxlan_mdb_flush()
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-09-25T05:09:51.783Z

Reserved: 2026-09-17T16:02:15.096Z

Link: CVE-2026-93250

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-09-24T16:17:21.187

Modified: 2026-09-25T05:17:00.980

Link: CVE-2026-93250

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-09-25T10:30:10Z

Weaknesses