---
id: CVE-2026-31680
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net: ipv6: flowlabel: defer exclusive option free until RCU teardown

  `ip6fl_seq_show()` walks the global flowlabel hash under the seq-file
  RCU read-side lock and print…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net: ipv6: flowlabel: defer exclusive option free until RCU teardown

  `ip6fl_seq_show()` walks the global flowlabel hash under the seq-file
  RCU read-side lock and print…
severity: high
cvss: 7.8
cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'
vendor: linux
product: linux_kernel
affected:
  - 'linux_kernel >= 3.9, < 5.10.253'
  - 'linux_kernel >= 5.11, < 5.15.203'
  - 'linux_kernel >= 5.16, < 6.1.168'
  - 'linux_kernel >= 6.2, < 6.6.134'
  - 'linux_kernel >= 6.7, < 6.12.81'
  - 'linux_kernel >= 6.13, < 6.18.22'
  - 'linux_kernel >= 6.19, < 6.19.12'
  - linux_kernel = 7.0
patched:
  - linux_kernel 6.19.12
published: '2026-04-25'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T02:19:16.850'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-31680'
references:
  - url: 'https://git.kernel.org/stable/c/3c54b66c83fb8fcbde8e6a7bf90b65856e39f827'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/414726b69921fe6355ae453f5b35e68dd078342a'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/4b6798024f7b2d535f3db1002c760143cdbd1bd3'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/572ce62778519a7d4d1c15f55dd2e45a474133c4'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/5a6b15f861b7c1304949e3350d23490a5fe429fd'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/6c7fbdb8ffde6413640de7cfbd7c976c353e89f8'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/8027964931785cb73d520ac70a342a3dc16c249b'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/9ca562bb8e66978b53028fa32b1a190708e6a091'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-019113.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-082556.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
  - url: 'https://cert-portal.siemens.com/productcert/html/ssa-457936.html'
    label: 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e
tags:
  - nvd
  - cve.org
epss: 0.00164
epssPercentile: 0.05534
ingestedAt: '2026-09-08T15:33:26.989Z'
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-10-16T15:12:23.036935Z'
---

## Overview

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

net: ipv6: flowlabel: defer exclusive option free until RCU teardown

`ip6fl_seq_show()` walks the global flowlabel hash under the seq-file
RCU read-side lock and prints `fl->opt->opt_nflen` when an option block
is present.

Exclusive flowlabels currently free `fl->opt` as soon as `fl->users`
drops to zero in `fl_release()`. However, the surrounding
`struct ip6_flowlabel` remains visible in the global hash table until
later garbage collection removes it and `fl_free_rcu()` finally tears it
down.

A concurrent `/proc/net/ip6_flowlabel` reader can therefore race that
early `kfree()` and dereference freed option state, triggering a crash
in `ip6fl_seq_show()`.

Fix this by keeping `fl->opt` alive until `fl_free_rcu()`. That matches
the lifetime already required for the enclosing flowlabel while readers
can still reach it under RCU.

## Affected

- `linux_kernel >= 3.9, < 5.10.253`
- `linux_kernel >= 5.11, < 5.15.203`
- `linux_kernel >= 5.16, < 6.1.168`
- `linux_kernel >= 6.2, < 6.6.134`
- `linux_kernel >= 6.7, < 6.12.81`
- `linux_kernel >= 6.13, < 6.18.22`
- `linux_kernel >= 6.19, < 6.19.12`
- `linux_kernel = 7.0`

## Remediation

Upgrade past the affected range:

- `linux_kernel 6.19.12`