---
id: CVE-2026-23351
title: 'netfilter: nft_set_pipapo: split gc into unlink and reclaim phase'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  netfilter: nft_set_pipapo: split gc into unlink and reclaim phase

  Yiming Qian reports Use-after-free in the pipapo set type:
    Under a large number of expired elements…
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 >= 3c4287f62044a90e73a561aa05fc46e62da173da <
    65ca51b9fb85477ab92a04295aed34b38f7c062e
  - >-
    Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da <
    c0f1f85097ac2b6e7d750fe4d05807985cd3fd3a
  - >-
    Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da <
    16f3595c0441d87dfa005c47d8f95be213afaa9e
  - >-
    Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da <
    7864c667aed01a58b87ca518a631322cd0ac34c0
  - >-
    Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da <
    c12d570d71920903a1a0468b7d13b085203d0c93
  - >-
    Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da <
    500a50a301ce962b019ab95053ac70264fec2c21
  - >-
    Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da <
    aff13667708dfa0dce136b8efd81baa9fa6ef261
  - >-
    Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da <
    9df95785d3d8302f7c066050117b04cd3c2048c2
  - Linux 5.6
published: '2026-03-25'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:45:42.212Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-23351'
references:
  - url: 'https://git.kernel.org/stable/c/65ca51b9fb85477ab92a04295aed34b38f7c062e'
  - url: 'https://git.kernel.org/stable/c/c0f1f85097ac2b6e7d750fe4d05807985cd3fd3a'
  - url: 'https://git.kernel.org/stable/c/16f3595c0441d87dfa005c47d8f95be213afaa9e'
  - url: 'https://git.kernel.org/stable/c/7864c667aed01a58b87ca518a631322cd0ac34c0'
  - url: 'https://git.kernel.org/stable/c/c12d570d71920903a1a0468b7d13b085203d0c93'
  - url: 'https://git.kernel.org/stable/c/500a50a301ce962b019ab95053ac70264fec2c21'
  - url: 'https://git.kernel.org/stable/c/aff13667708dfa0dce136b8efd81baa9fa6ef261'
  - url: 'https://git.kernel.org/stable/c/9df95785d3d8302f7c066050117b04cd3c2048c2'
tags:
  - cve.org
epss: 0.00125
epssPercentile: 0.01865
ingestedAt: '2026-09-08T15:33:26.993Z'
---

## Overview

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

netfilter: nft_set_pipapo: split gc into unlink and reclaim phase

Yiming Qian reports Use-after-free in the pipapo set type:
  Under a large number of expired elements, commit-time GC can run for a very
  long time in a non-preemptible context, triggering soft lockup warnings and
  RCU stall reports (local denial of service).

We must split GC in an unlink and a reclaim phase.

We cannot queue elements for freeing until pointers have been swapped.
Expired elements are still exposed to both the packet path and userspace
dumpers via the live copy of the data structure.

call_rcu() does not protect us: dump operations or element lookups starting
after call_rcu has fired can still observe the free'd element, unless the
commit phase has made enough progress to swap the clone and live pointers
before any new reader has picked up the old version.

This a similar approach as done recently for the rbtree backend in commit
35f83a75529a ("netfilter: nft_set_rbtree: don't gc elements on insert").

## Affected

- `Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < 65ca51b9fb85477ab92a04295aed34b38f7c062e`
- `Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < c0f1f85097ac2b6e7d750fe4d05807985cd3fd3a`
- `Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < 16f3595c0441d87dfa005c47d8f95be213afaa9e`
- `Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < 7864c667aed01a58b87ca518a631322cd0ac34c0`
- `Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < c12d570d71920903a1a0468b7d13b085203d0c93`
- `Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < 500a50a301ce962b019ab95053ac70264fec2c21`
- `Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < aff13667708dfa0dce136b8efd81baa9fa6ef261`
- `Linux >= 3c4287f62044a90e73a561aa05fc46e62da173da < 9df95785d3d8302f7c066050117b04cd3c2048c2`
- `Linux 5.6`

## Remediation

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