---
id: CVE-2026-45859
title: 'netfilter: nfnetlink_queue: do shared-unconfirmed check before segmentation'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  netfilter: nfnetlink_queue: do shared-unconfirmed check before segmentation

  Ulrich reports a regression with nfqueue:

  If an application did not set the 'F_GSO' capabi…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 7d8dc1c7be8d3509e8f5164dd5df64c8e34d7eeb <
    79b713ef4261a8ead96af4703f89d0b5f25532e2
  - >-
    Linux >= 7d8dc1c7be8d3509e8f5164dd5df64c8e34d7eeb <
    23901aa6b8a2f294c4b774436b4691f3ff863a8f
  - >-
    Linux >= 7d8dc1c7be8d3509e8f5164dd5df64c8e34d7eeb <
    b740e7ddd7ca0dbfeafca3f5e52717206cf28524
  - >-
    Linux >= 7d8dc1c7be8d3509e8f5164dd5df64c8e34d7eeb <
    207b3ebacb6113acaaec0d171d5307032c690004
  - Linux 6c4a0ba674f410ab99a30a16f32dac0ebfed5cd3
  - Linux 6dcc8ba8a6074bb79040f502dc66ad23a58a1c86
  - Linux 74e6eb7fd27ef1ccc68041dbc66e6d80d2e4a1a0
  - Linux 025b3326c5c409b372d0103ad30f174e55adbd1b
  - Linux >= 5.15.166 < 5.16
  - Linux >= 6.1.107 < 6.2
  - Linux >= 6.6.48 < 6.7
  - Linux >= 6.10.7 < 6.11
  - Linux 6.11
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-16T15:18:05.838159Z'
published: '2026-05-27'
updated: '2026-10-16'
sourceUpdated: '2026-10-16T15:20:45.559Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-45859'
references:
  - url: 'https://git.kernel.org/stable/c/79b713ef4261a8ead96af4703f89d0b5f25532e2'
  - url: 'https://git.kernel.org/stable/c/23901aa6b8a2f294c4b774436b4691f3ff863a8f'
  - url: 'https://git.kernel.org/stable/c/b740e7ddd7ca0dbfeafca3f5e52717206cf28524'
  - url: 'https://git.kernel.org/stable/c/207b3ebacb6113acaaec0d171d5307032c690004'
tags:
  - cve.org
epss: 0.00612
epssPercentile: 0.4824
ingestedAt: '2026-10-16T17:24:46.699Z'
---

## Overview

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

netfilter: nfnetlink_queue: do shared-unconfirmed check before segmentation

Ulrich reports a regression with nfqueue:

If an application did not set the 'F_GSO' capability flag and a gso
packet with an unconfirmed nf_conn entry is received all packets are
now dropped instead of queued, because the check happens after
skb_gso_segment().  In that case, we did have exclusive ownership
of the skb and its associated conntrack entry.  The elevated use
count is due to skb_clone happening via skb_gso_segment().

Move the check so that its peformed vs. the aggregated packet.

Then, annotate the individual segments except the first one so we
can do a 2nd check at reinject time.

For the normal case, where userspace does in-order reinjects, this avoids
packet drops: first reinjected segment continues traversal and confirms
entry, remaining segments observe the confirmed entry.

While at it, simplify nf_ct_drop_unconfirmed(): We only care about
unconfirmed entries with a refcnt > 1, there is no need to special-case
dying entries.

This only happens with UDP.  With TCP, the only unconfirmed packet will
be the TCP SYN, those aren't aggregated by GRO.

Next patch adds a udpgro test case to cover this scenario.

## Affected

- `Linux >= 7d8dc1c7be8d3509e8f5164dd5df64c8e34d7eeb < 79b713ef4261a8ead96af4703f89d0b5f25532e2`
- `Linux >= 7d8dc1c7be8d3509e8f5164dd5df64c8e34d7eeb < 23901aa6b8a2f294c4b774436b4691f3ff863a8f`
- `Linux >= 7d8dc1c7be8d3509e8f5164dd5df64c8e34d7eeb < b740e7ddd7ca0dbfeafca3f5e52717206cf28524`
- `Linux >= 7d8dc1c7be8d3509e8f5164dd5df64c8e34d7eeb < 207b3ebacb6113acaaec0d171d5307032c690004`
- `Linux 6c4a0ba674f410ab99a30a16f32dac0ebfed5cd3`
- `Linux 6dcc8ba8a6074bb79040f502dc66ad23a58a1c86`
- `Linux 74e6eb7fd27ef1ccc68041dbc66e6d80d2e4a1a0`
- `Linux 025b3326c5c409b372d0103ad30f174e55adbd1b`
- `Linux >= 5.15.166 < 5.16`
- `Linux >= 6.1.107 < 6.2`
- `Linux >= 6.6.48 < 6.7`
- `Linux >= 6.10.7 < 6.11`
- `Linux 6.11`

## Remediation

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