---
id: CVE-2025-38037
title: 'vxlan: Annotate FDB data races'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  vxlan: Annotate FDB data races

  The 'used' and 'updated' fields in the FDB entry structure can be
  accessed concurrently by multiple threads, leading to reports such as
  …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 <
    02a33b1035a307453a1da6ce0a1bf3676be287d7
  - >-
    Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 <
    87d076987a9ba106c83412fcd113656f71af05a1
  - >-
    Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 <
    e033da39fc6abbddab6c29624acef80757f273fa
  - >-
    Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 <
    784b78295a3a58bf052339dd669e6e03710220d3
  - >-
    Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 <
    13cba3f837903f7184d6e9b6137d5165ffe82a8f
  - >-
    Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 <
    a6644aeb8ddf196dec5f8e782293c36f065df4d7
  - >-
    Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 <
    4eceb7eae6ea7c950384c34e6dbbe872c981935f
  - >-
    Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 <
    f6205f8215f12a96518ac9469ff76294ae7bd612
  - Linux 3.7
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-05T20:48:26.208696Z'
published: '2025-06-18'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T20:52:13.124Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-38037'
references:
  - url: 'https://git.kernel.org/stable/c/02a33b1035a307453a1da6ce0a1bf3676be287d7'
  - url: 'https://git.kernel.org/stable/c/87d076987a9ba106c83412fcd113656f71af05a1'
  - url: 'https://git.kernel.org/stable/c/e033da39fc6abbddab6c29624acef80757f273fa'
  - url: 'https://git.kernel.org/stable/c/784b78295a3a58bf052339dd669e6e03710220d3'
  - url: 'https://git.kernel.org/stable/c/13cba3f837903f7184d6e9b6137d5165ffe82a8f'
  - url: 'https://git.kernel.org/stable/c/a6644aeb8ddf196dec5f8e782293c36f065df4d7'
  - url: 'https://git.kernel.org/stable/c/4eceb7eae6ea7c950384c34e6dbbe872c981935f'
  - url: 'https://git.kernel.org/stable/c/f6205f8215f12a96518ac9469ff76294ae7bd612'
tags:
  - cve.org
epss: 0.00223
epssPercentile: 0.12973
ingestedAt: '2026-11-05T22:38:31.909Z'
---

## Overview

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

vxlan: Annotate FDB data races

The 'used' and 'updated' fields in the FDB entry structure can be
accessed concurrently by multiple threads, leading to reports such as
[1]. Can be reproduced using [2].

Suppress these reports by annotating these accesses using
READ_ONCE() / WRITE_ONCE().

[1]
BUG: KCSAN: data-race in vxlan_xmit / vxlan_xmit

write to 0xffff942604d263a8 of 8 bytes by task 286 on cpu 0:
 vxlan_xmit+0xb29/0x2380
 dev_hard_start_xmit+0x84/0x2f0
 __dev_queue_xmit+0x45a/0x1650
 packet_xmit+0x100/0x150
 packet_sendmsg+0x2114/0x2ac0
 __sys_sendto+0x318/0x330
 __x64_sys_sendto+0x76/0x90
 x64_sys_call+0x14e8/0x1c00
 do_syscall_64+0x9e/0x1a0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff942604d263a8 of 8 bytes by task 287 on cpu 2:
 vxlan_xmit+0xadf/0x2380
 dev_hard_start_xmit+0x84/0x2f0
 __dev_queue_xmit+0x45a/0x1650
 packet_xmit+0x100/0x150
 packet_sendmsg+0x2114/0x2ac0
 __sys_sendto+0x318/0x330
 __x64_sys_sendto+0x76/0x90
 x64_sys_call+0x14e8/0x1c00
 do_syscall_64+0x9e/0x1a0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x00000000fffbac6e -> 0x00000000fffbac6f

Reported by Kernel Concurrency Sanitizer on:
CPU: 2 UID: 0 PID: 287 Comm: mausezahn Not tainted 6.13.0-rc7-01544-gb4b270f11a02 #5
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-3.fc41 04/01/2014

[2]
 #!/bin/bash

 set +H
 echo whitelist > /sys/kernel/debug/kcsan
 echo !vxlan_xmit > /sys/kernel/debug/kcsan

 ip link add name vx0 up type vxlan id 10010 dstport 4789 local 192.0.2.1
 bridge fdb add 00:11:22:33:44:55 dev vx0 self static dst 198.51.100.1
 taskset -c 0 mausezahn vx0 -a own -b 00:11:22:33:44:55 -c 0 -q &
 taskset -c 2 mausezahn vx0 -a own -b 00:11:22:33:44:55 -c 0 -q &

## Affected

- `Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 < 02a33b1035a307453a1da6ce0a1bf3676be287d7`
- `Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 < 87d076987a9ba106c83412fcd113656f71af05a1`
- `Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 < e033da39fc6abbddab6c29624acef80757f273fa`
- `Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 < 784b78295a3a58bf052339dd669e6e03710220d3`
- `Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 < 13cba3f837903f7184d6e9b6137d5165ffe82a8f`
- `Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 < a6644aeb8ddf196dec5f8e782293c36f065df4d7`
- `Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 < 4eceb7eae6ea7c950384c34e6dbbe872c981935f`
- `Linux >= d342894c5d2f8c7df194c793ec4059656e09ca31 < f6205f8215f12a96518ac9469ff76294ae7bd612`
- `Linux 3.7`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.