CVE-2026-98023 - Vulnerability Details

- vxlan: reject dynamic fdb entries that reference a nexthop id

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.

Published: 2026-09-25

Score: 7.8 High

EPSS: < 1% Very Low

KEV: No

Impact:

Action:

Analysis

Impact

In the Linux kernel, the VXLAN driver permits dynamic forwarding database (FDB) entries that reference FDB nexthops to be configured even though proper locking is absent. When two VXLAN devices share the same nexthop list, concurrent add or delete operations can race, corrupting the internal list, triggering KASAN warnings, and ultimately causing a kernel crash. This memory corruption can destabilize the operating system.

Affected Systems

All Linux kernel releases prior to the commit that rejects dynamic FDB entries referencing nexthops are vulnerable. Because no specific kernel version range is supplied, every kernel version before the fix across all distributions that ship an older kernel is covered.

Risk and Exploitability

The CVSS base score of 7.8 indicates high severity. The EPSS score is less than 1%, implying a very low public exploitation probability, and the vulnerability is not listed in the CISA KEV catalog. Exploitation requires modifying the VXLAN configuration, which is typically a privileged operation. When achieved, it can trigger a kernel crash.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions

Linux

unaffected

Version	Status	Constraints
`1274e1cc42264d4e629841e4f182795cb0becfd2`	affected	< 00c7f4b8144e535ffb931ad45942a1bd1315b882
`1274e1cc42264d4e629841e4f182795cb0becfd2`	affected	< 55a33882808f1402052d53a08ead59aff8af18a1
`1274e1cc42264d4e629841e4f182795cb0becfd2`	affected	< c8f29af91e0830fdabc9aa1eb1a0f898ce1bc603
`1274e1cc42264d4e629841e4f182795cb0becfd2`	affected	< b2a8e165ddb6cd72176890b2954c52b0f6dbce1a
`1274e1cc42264d4e629841e4f182795cb0becfd2`	affected	< 28f86eec851b7406a4bc6143f82aeba2882d9842
`1274e1cc42264d4e629841e4f182795cb0becfd2`	affected	< 53359916ceb649b7e6947c8c2f669368a41c1354
`1274e1cc42264d4e629841e4f182795cb0becfd2`	affected	< 3fa64d86fc64eda104e3e97721a12a42a2fd2073
`1274e1cc42264d4e629841e4f182795cb0becfd2`	affected	< 98fc57d167446b95b4e719815fe79edef93f8e7a

Linux

affected

Version	Status	Constraints
`5.8`	affected	—
`0`	unaffected	< 5.8
`5.10.271`	unaffected	≤ 5.10.*
`5.15.222`	unaffected	≤ 5.15.*
`6.1.189`	unaffected	≤ 6.1.*
`6.6.158`	unaffected	≤ 6.6.*
`6.12.111`	unaffected	≤ 6.12.*
`6.18.53`	unaffected	≤ 6.18.*
`7.2.7`	unaffected	≤ 7.2.*
`7.3`	unaffected	≤ *

No data.

Vendor Product Confidence Versions

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`[1274e1cc42264d4e629841e4f182795cb0becfd2,28f86eec851b7406a4bc6143f82aeba2882d9842)`	affected	code_commit	—
`[1274e1cc42264d4e629841e4f182795cb0becfd2,53359916ceb649b7e6947c8c2f669368a41c1354)`	affected	code_commit	—
`[1274e1cc42264d4e629841e4f182795cb0becfd2,3fa64d86fc64eda104e3e97721a12a42a2fd2073)`	affected	code_commit	—
`[1274e1cc42264d4e629841e4f182795cb0becfd2,98fc57d167446b95b4e719815fe79edef93f8e7a)`	affected	code_commit	—

Linux

Linux Kernel

99%

Version	Status	Scheme	Platform
`5.8`	affected	generic	—
`[0,5.8)`	unaffected	generic	—
`[6.12.111,6.13.0)`	unaffected	semver	—
`[6.18.53,6.19.0)`	unaffected	semver	—
`[7.2.7,7.3.0)`	unaffected	semver	—
`[7.3-rc3,*]`	unaffected	generic	—

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Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

Upgrade the system to a kernel version that includes the commit rejecting dynamic FDB entries that reference nexthops
Reboot into the updated kernel to activate the fix
Verify that no VXLAN FDB entries use the dynamic flag with a nexthop and that configuration scripts enforce this restriction

Generated by OpenCVE AI on September 30, 2026 at 15:14 UTC.

Tracking

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Advisories

Source	ID	Title
Debian DLA	DLA-4817-1	linux-6.12 security update
Debian DLA	DLA-4841-1	linux security update
Debian DSA	DSA-6528-1	linux security update
Ubuntu USN	USN-8961-1	Linux kernel vulnerabilities

No CVSS v4.0

Attack Vector Local

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

The EPSS score is 0.00126.

Key SSVC decision points have not yet been added.

References

Link	Providers
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98023.mbox
https://git.kernel.org/stable/c/00c7f4b8144e535ffb931ad45942a1bd1315b882
https://git.kernel.org/stable/c/28f86eec851b7406a4bc6143f82aeba2882d9842
https://git.kernel.org/stable/c/3fa64d86fc64eda104e3e97721a12a42a2fd2073
https://git.kernel.org/stable/c/53359916ceb649b7e6947c8c2f669368a41c1354
https://git.kernel.org/stable/c/55a33882808f1402052d53a08ead59aff8af18a1
https://git.kernel.org/stable/c/98fc57d167446b95b4e719815fe79edef93f8e7a
https://git.kernel.org/stable/c/b2a8e165ddb6cd72176890b2954c52b0f6dbce1a
https://git.kernel.org/stable/c/c8f29af91e0830fdabc9aa1eb1a0f898ce1bc603
https://nvd.nist.gov/vuln/detail/CVE-2026-98023
https://www.cve.org/CVERecord?id=CVE-2026-98023

History

Sat, 03 Oct 2026 11:15:00 +0000

Type	Values Removed	Values Added
References		https://git.kernel.org/stable/c/00c7f4b8144e535ffb931ad45942a1bd1315b882 https://git.kernel.org/stable/c/55a33882808f1402052d53a08ead59aff8af18a1 https://git.kernel.org/stable/c/b2a8e165ddb6cd72176890b2954c52b0f6dbce1a https://git.kernel.org/stable/c/c8f29af91e0830fdabc9aa1eb1a0f898ce1bc603

Tue, 29 Sep 2026 20:30:00 +0000

Type	Values Removed	Values Added
Weaknesses	CWE-362

Tue, 29 Sep 2026 13:15:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-413
References		https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98023.mbox https://nvd.nist.gov/vuln/detail/CVE-2026-98023 https://www.cve.org/CVERecord?id=CVE-2026-98023
Metrics	threat_severity `None`	threat_severity `Moderate`

Fri, 25 Sep 2026 22:15:00 +0000

Type	Values Removed	Values Added
Weaknesses		CWE-362

Fri, 25 Sep 2026 15:00:00 +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'}`

Fri, 25 Sep 2026 10:30:00 +0000

Type	Values Removed	Values Added
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.
Title		vxlan: reject dynamic fdb entries that reference a nexthop id
First Time appeared		Linux Linux linux Kernel
CPEs		cpe:2.3:o:linux:linux_kernel::::::::
Vendors & Products		Linux Linux linux Kernel
References		https://git.kernel.org/stable/c/28f86eec851b7406a4bc6143f82aeba2882d9842 https://git.kernel.org/stable/c/3fa64d86fc64eda104e3e97721a12a42a2fd2073 https://git.kernel.org/stable/c/53359916ceb649b7e6947c8c2f669368a41c1354 https://git.kernel.org/stable/c/98fc57d167446b95b4e719815fe79edef93f8e7a

Subscriptions

Linux Linux Kernel

MITRE

Status: PUBLISHED

Assigner: Linux

Published: 2026-09-25T10:23:42.706Z

Updated: 2026-10-19T09:12:28.386Z

Reserved: 2026-09-25T10:19:56.069Z

Link: CVE-2026-98023

Vulnrichment

No data.

NVD

Status : Received

Published: 2026-09-25T11:17:30.873

Modified: 2026-10-19T10:17:56.200

Link: CVE-2026-98023

Redhat

Severity : Moderate

Publid Date: 2026-09-25T00:00:00Z

Links: CVE-2026-98023 - Bugzilla

OpenCVE Enrichment

Updated: 2026-09-30T15:15:16Z

Weaknesses

CWE-413
Improper Resource Locking

Impact

Affected Systems

Risk and Exploitability

Tracking

Attack Vector Local

Attack Complexity Low

Privileges Required Low

Scope Unchanged

Confidentiality Impact High

Integrity Impact High

Availability Impact High

User Interaction None

Subscriptions

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