---
id: CVE-2025-39894
title: >-
  netfilter: br_netfilter: do not check confirmed bit in br_nf_local_in() after
  confirm
summary: >-
  In the Linux kernel, the following vulnerability has been resolved:


  netfilter: br_netfilter: do not check confirmed bit in br_nf_local_in() after
  confirm


  When send a broadcast packet to a tap device, which was added to a bridge,

  br_nf_…
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 >= 7c3f28599652acf431a2211168de4a583f30b6d5 <
    d00c8b0daf56012f69075e3377da67878c775e4c
  - >-
    Linux >= 2b1414d5e94e477edff1d2c79030f1d742625ea0 <
    ccbad4803225eafe0175d3cb19f0d8d73b504a94
  - >-
    Linux >= 80cd0487f630b5382734997c3e5e3003a77db315 <
    50db11e2bbb635e38e3dd096215580d6adb41fb0
  - >-
    Linux >= 62e7151ae3eb465e0ab52a20c941ff33bb6332e9 <
    c47ca77fee9071aa543bae592dd2a384f895c8b6
  - >-
    Linux >= 62e7151ae3eb465e0ab52a20c941ff33bb6332e9 <
    a74abcf0f09f59daeecf7a3ba9c1d690808b0afe
  - >-
    Linux >= 62e7151ae3eb465e0ab52a20c941ff33bb6332e9 <
    479a54ab92087318514c82428a87af2d7af1a576
  - Linux cb734975b0ffa688ff6cc0eed463865bf07b6c01
  - Linux >= 5.15.151 < 5.15.192
  - Linux >= 6.1.81 < 6.1.151
  - Linux >= 6.6.21 < 6.6.105
  - Linux >= 6.7.9 < 6.8
  - Linux 6.8
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-15T21:54:35.991421Z'
published: '2025-10-01'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T22:02:32.869Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-39894'
references:
  - url: 'https://git.kernel.org/stable/c/d00c8b0daf56012f69075e3377da67878c775e4c'
  - url: 'https://git.kernel.org/stable/c/ccbad4803225eafe0175d3cb19f0d8d73b504a94'
  - url: 'https://git.kernel.org/stable/c/50db11e2bbb635e38e3dd096215580d6adb41fb0'
  - url: 'https://git.kernel.org/stable/c/c47ca77fee9071aa543bae592dd2a384f895c8b6'
  - url: 'https://git.kernel.org/stable/c/a74abcf0f09f59daeecf7a3ba9c1d690808b0afe'
  - url: 'https://git.kernel.org/stable/c/479a54ab92087318514c82428a87af2d7af1a576'
tags:
  - cve.org
epss: 0.00332
epssPercentile: 0.26196
ingestedAt: '2026-10-15T22:48:25.529Z'
---

## Overview

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

netfilter: br_netfilter: do not check confirmed bit in br_nf_local_in() after confirm

When send a broadcast packet to a tap device, which was added to a bridge,
br_nf_local_in() is called to confirm the conntrack. If another conntrack
with the same hash value is added to the hash table, which can be
triggered by a normal packet to a non-bridge device, the below warning
may happen.

  ------------[ cut here ]------------
  WARNING: CPU: 1 PID: 96 at net/bridge/br_netfilter_hooks.c:632 br_nf_local_in+0x168/0x200
  CPU: 1 UID: 0 PID: 96 Comm: tap_send Not tainted 6.17.0-rc2-dirty #44 PREEMPT(voluntary)
  RIP: 0010:br_nf_local_in+0x168/0x200
  Call Trace:
   <TASK>
   nf_hook_slow+0x3e/0xf0
   br_pass_frame_up+0x103/0x180
   br_handle_frame_finish+0x2de/0x5b0
   br_nf_hook_thresh+0xc0/0x120
   br_nf_pre_routing_finish+0x168/0x3a0
   br_nf_pre_routing+0x237/0x5e0
   br_handle_frame+0x1ec/0x3c0
   __netif_receive_skb_core+0x225/0x1210
   __netif_receive_skb_one_core+0x37/0xa0
   netif_receive_skb+0x36/0x160
   tun_get_user+0xa54/0x10c0
   tun_chr_write_iter+0x65/0xb0
   vfs_write+0x305/0x410
   ksys_write+0x60/0xd0
   do_syscall_64+0xa4/0x260
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
   </TASK>
  ---[ end trace 0000000000000000 ]---

To solve the hash conflict, nf_ct_resolve_clash() try to merge the
conntracks, and update skb->_nfct. However, br_nf_local_in() still use the
old ct from local variable 'nfct' after confirm(), which leads to this
warning.

If confirm() does not insert the conntrack entry and return NF_DROP, the
warning may also occur. There is no need to reserve the WARN_ON_ONCE, just
remove it.

## Affected

- `Linux >= 7c3f28599652acf431a2211168de4a583f30b6d5 < d00c8b0daf56012f69075e3377da67878c775e4c`
- `Linux >= 2b1414d5e94e477edff1d2c79030f1d742625ea0 < ccbad4803225eafe0175d3cb19f0d8d73b504a94`
- `Linux >= 80cd0487f630b5382734997c3e5e3003a77db315 < 50db11e2bbb635e38e3dd096215580d6adb41fb0`
- `Linux >= 62e7151ae3eb465e0ab52a20c941ff33bb6332e9 < c47ca77fee9071aa543bae592dd2a384f895c8b6`
- `Linux >= 62e7151ae3eb465e0ab52a20c941ff33bb6332e9 < a74abcf0f09f59daeecf7a3ba9c1d690808b0afe`
- `Linux >= 62e7151ae3eb465e0ab52a20c941ff33bb6332e9 < 479a54ab92087318514c82428a87af2d7af1a576`
- `Linux cb734975b0ffa688ff6cc0eed463865bf07b6c01`
- `Linux >= 5.15.151 < 5.15.192`
- `Linux >= 6.1.81 < 6.1.151`
- `Linux >= 6.6.21 < 6.6.105`
- `Linux >= 6.7.9 < 6.8`
- `Linux 6.8`

## Remediation

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