---
id: CVE-2026-31680
title: 'net: ipv6: flowlabel: defer exclusive option free until RCU teardown'
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'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 <
    4b6798024f7b2d535f3db1002c760143cdbd1bd3
  - >-
    Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 <
    3c54b66c83fb8fcbde8e6a7bf90b65856e39f827
  - >-
    Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 <
    5a6b15f861b7c1304949e3350d23490a5fe429fd
  - >-
    Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 <
    6c7fbdb8ffde6413640de7cfbd7c976c353e89f8
  - >-
    Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 <
    8027964931785cb73d520ac70a342a3dc16c249b
  - >-
    Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 <
    414726b69921fe6355ae453f5b35e68dd078342a
  - >-
    Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 <
    572ce62778519a7d4d1c15f55dd2e45a474133c4
  - >-
    Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 <
    9ca562bb8e66978b53028fa32b1a190708e6a091
  - Linux 3.9
published: '2026-04-25'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:48:05.243Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-31680'
references:
  - url: 'https://git.kernel.org/stable/c/4b6798024f7b2d535f3db1002c760143cdbd1bd3'
  - url: 'https://git.kernel.org/stable/c/3c54b66c83fb8fcbde8e6a7bf90b65856e39f827'
  - url: 'https://git.kernel.org/stable/c/5a6b15f861b7c1304949e3350d23490a5fe429fd'
  - url: 'https://git.kernel.org/stable/c/6c7fbdb8ffde6413640de7cfbd7c976c353e89f8'
  - url: 'https://git.kernel.org/stable/c/8027964931785cb73d520ac70a342a3dc16c249b'
  - url: 'https://git.kernel.org/stable/c/414726b69921fe6355ae453f5b35e68dd078342a'
  - url: 'https://git.kernel.org/stable/c/572ce62778519a7d4d1c15f55dd2e45a474133c4'
  - url: 'https://git.kernel.org/stable/c/9ca562bb8e66978b53028fa32b1a190708e6a091'
tags:
  - cve.org
epss: 0.00184
epssPercentile: 0.07086
ingestedAt: '2026-09-08T15:33:26.989Z'
---

## 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 >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 4b6798024f7b2d535f3db1002c760143cdbd1bd3`
- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 3c54b66c83fb8fcbde8e6a7bf90b65856e39f827`
- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 5a6b15f861b7c1304949e3350d23490a5fe429fd`
- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 6c7fbdb8ffde6413640de7cfbd7c976c353e89f8`
- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 8027964931785cb73d520ac70a342a3dc16c249b`
- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 414726b69921fe6355ae453f5b35e68dd078342a`
- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 572ce62778519a7d4d1c15f55dd2e45a474133c4`
- `Linux >= d3aedd5ebd4b0b925b0bcda548066803e1318499 < 9ca562bb8e66978b53028fa32b1a190708e6a091`
- `Linux 3.9`

## Remediation

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