---
id: CVE-2025-38721
title: 'netfilter: ctnetlink: fix refcount leak on table dump'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  netfilter: ctnetlink: fix refcount leak on table dump

  There is a reference count leak in ctnetlink_dump_table():
        if (res < 0) {
                  nf_conntrack_get(…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 <
    586892e341fbf698e7cbaca293e1353957db725a
  - >-
    Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 <
    962518c6ca9f9a13df099cafa429f72f68ad61f0
  - >-
    Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 <
    19b909a4b1452fb97e477d2f08b97f8d04095619
  - >-
    Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 <
    41462f4cfc583513833f87f9ee55d12da651a7e3
  - >-
    Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 <
    30cf811058552b8cd0e98dff677ef3f89d6d34ce
  - >-
    Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 <
    a2cb4df7872de069f809de2f076ec8e54d649fe3
  - >-
    Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 <
    e14f72aa66c029db106921d621edcedef68e065b
  - >-
    Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 <
    a62d6aa3f31f216b637a4c71b7a8bfc7c57f049b
  - >-
    Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 <
    de788b2e6227462b6dcd0e07474e72c089008f74
  - Linux 2.6.18
published: '2025-09-04'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:41:58.463Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-38721'
references:
  - url: 'https://git.kernel.org/stable/c/586892e341fbf698e7cbaca293e1353957db725a'
  - url: 'https://git.kernel.org/stable/c/962518c6ca9f9a13df099cafa429f72f68ad61f0'
  - url: 'https://git.kernel.org/stable/c/19b909a4b1452fb97e477d2f08b97f8d04095619'
  - url: 'https://git.kernel.org/stable/c/41462f4cfc583513833f87f9ee55d12da651a7e3'
  - url: 'https://git.kernel.org/stable/c/30cf811058552b8cd0e98dff677ef3f89d6d34ce'
  - url: 'https://git.kernel.org/stable/c/a2cb4df7872de069f809de2f076ec8e54d649fe3'
  - url: 'https://git.kernel.org/stable/c/e14f72aa66c029db106921d621edcedef68e065b'
  - url: 'https://git.kernel.org/stable/c/a62d6aa3f31f216b637a4c71b7a8bfc7c57f049b'
  - url: 'https://git.kernel.org/stable/c/de788b2e6227462b6dcd0e07474e72c089008f74'
tags:
  - cve.org
epss: 0.00169
epssPercentile: 0.05479
ingestedAt: '2026-09-08T15:33:26.997Z'
---

## Overview

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

netfilter: ctnetlink: fix refcount leak on table dump

There is a reference count leak in ctnetlink_dump_table():
      if (res < 0) {
                nf_conntrack_get(&ct->ct_general); // HERE
                cb->args[1] = (unsigned long)ct;
                ...

While its very unlikely, its possible that ct == last.
If this happens, then the refcount of ct was already incremented.
This 2nd increment is never undone.

This prevents the conntrack object from being released, which in turn
keeps prevents cnet->count from dropping back to 0.

This will then block the netns dismantle (or conntrack rmmod) as
nf_conntrack_cleanup_net_list() will wait forever.

This can be reproduced by running conntrack_resize.sh selftest in a loop.
It takes ~20 minutes for me on a preemptible kernel on average before
I see a runaway kworker spinning in nf_conntrack_cleanup_net_list.

One fix would to change this to:
        if (res < 0) {
		if (ct != last)
	                nf_conntrack_get(&ct->ct_general);

But this reference counting isn't needed in the first place.
We can just store a cookie value instead.

A followup patch will do the same for ctnetlink_exp_dump_table,
it looks to me as if this has the same problem and like
ctnetlink_dump_table, we only need a 'skip hint', not the actual
object so we can apply the same cookie strategy there as well.

## Affected

- `Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 < 586892e341fbf698e7cbaca293e1353957db725a`
- `Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 < 962518c6ca9f9a13df099cafa429f72f68ad61f0`
- `Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 < 19b909a4b1452fb97e477d2f08b97f8d04095619`
- `Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 < 41462f4cfc583513833f87f9ee55d12da651a7e3`
- `Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 < 30cf811058552b8cd0e98dff677ef3f89d6d34ce`
- `Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 < a2cb4df7872de069f809de2f076ec8e54d649fe3`
- `Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 < e14f72aa66c029db106921d621edcedef68e065b`
- `Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 < a62d6aa3f31f216b637a4c71b7a8bfc7c57f049b`
- `Linux >= d205dc40798d97d63ad348bfaf7394f445d152d4 < de788b2e6227462b6dcd0e07474e72c089008f74`
- `Linux 2.6.18`

## Remediation

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