---
id: CVE-2025-39980
title: 'nexthop: Forbid FDB status change while nexthop is in a group'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  nexthop: Forbid FDB status change while nexthop is in a group

  The kernel forbids the creation of non-FDB nexthop groups with FDB
  nexthops:

   # ip nexthop add id 1 via …
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 <
    e1e87ac0daacd51f522ecd1645cd76b5809303ed
  - >-
    Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 <
    0e7bfe7a268ccbd7859730c529161cafbf44637c
  - >-
    Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 <
    ec428fff792b7bd15b248dafca2e654b666b1304
  - >-
    Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 <
    24046d31f6f92220852d393d510b6062843e3fbd
  - >-
    Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 <
    f0e49fd13afe9dea7a09a1c9537fd00cea22badb
  - >-
    Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 <
    8dd4aa0122885f710930de135af2adc4ccc3238f
  - >-
    Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 <
    390b3a300d7872cef9588f003b204398be69ce08
  - Linux 5.8
published: '2025-10-15'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:42:41.996Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2025-39980'
references:
  - url: 'https://git.kernel.org/stable/c/e1e87ac0daacd51f522ecd1645cd76b5809303ed'
  - url: 'https://git.kernel.org/stable/c/0e7bfe7a268ccbd7859730c529161cafbf44637c'
  - url: 'https://git.kernel.org/stable/c/ec428fff792b7bd15b248dafca2e654b666b1304'
  - url: 'https://git.kernel.org/stable/c/24046d31f6f92220852d393d510b6062843e3fbd'
  - url: 'https://git.kernel.org/stable/c/f0e49fd13afe9dea7a09a1c9537fd00cea22badb'
  - url: 'https://git.kernel.org/stable/c/8dd4aa0122885f710930de135af2adc4ccc3238f'
  - url: 'https://git.kernel.org/stable/c/390b3a300d7872cef9588f003b204398be69ce08'
tags:
  - cve.org
epss: 0.00211
epssPercentile: 0.10176
ingestedAt: '2026-09-08T15:33:26.996Z'
---

## Overview

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

nexthop: Forbid FDB status change while nexthop is in a group

The kernel forbids the creation of non-FDB nexthop groups with FDB
nexthops:

 # ip nexthop add id 1 via 192.0.2.1 fdb
 # ip nexthop add id 2 group 1
 Error: Non FDB nexthop group cannot have fdb nexthops.

And vice versa:

 # ip nexthop add id 3 via 192.0.2.2 dev dummy1
 # ip nexthop add id 4 group 3 fdb
 Error: FDB nexthop group can only have fdb nexthops.

However, as long as no routes are pointing to a non-FDB nexthop group,
the kernel allows changing the type of a nexthop from FDB to non-FDB and
vice versa:

 # ip nexthop add id 5 via 192.0.2.2 dev dummy1
 # ip nexthop add id 6 group 5
 # ip nexthop replace id 5 via 192.0.2.2 fdb
 # echo $?
 0

This configuration is invalid and can result in a NPD [1] since FDB
nexthops are not associated with a nexthop device:

 # ip route add 198.51.100.1/32 nhid 6
 # ping 198.51.100.1

Fix by preventing nexthop FDB status change while the nexthop is in a
group:

 # ip nexthop add id 7 via 192.0.2.2 dev dummy1
 # ip nexthop add id 8 group 7
 # ip nexthop replace id 7 via 192.0.2.2 fdb
 Error: Cannot change nexthop FDB status while in a group.

[1]
BUG: kernel NULL pointer dereference, address: 00000000000003c0
[...]
Oops: Oops: 0000 [#1] SMP
CPU: 6 UID: 0 PID: 367 Comm: ping Not tainted 6.17.0-rc6-virtme-gb65678cacc03 #1 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.17.0-4.fc41 04/01/2014
RIP: 0010:fib_lookup_good_nhc+0x1e/0x80
[...]
Call Trace:
 <TASK>
 fib_table_lookup+0x541/0x650
 ip_route_output_key_hash_rcu+0x2ea/0x970
 ip_route_output_key_hash+0x55/0x80
 __ip4_datagram_connect+0x250/0x330
 udp_connect+0x2b/0x60
 __sys_connect+0x9c/0xd0
 __x64_sys_connect+0x18/0x20
 do_syscall_64+0xa4/0x2a0
 entry_SYSCALL_64_after_hwframe+0x4b/0x53

## Affected

- `Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 < e1e87ac0daacd51f522ecd1645cd76b5809303ed`
- `Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 < 0e7bfe7a268ccbd7859730c529161cafbf44637c`
- `Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 < ec428fff792b7bd15b248dafca2e654b666b1304`
- `Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 < 24046d31f6f92220852d393d510b6062843e3fbd`
- `Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 < f0e49fd13afe9dea7a09a1c9537fd00cea22badb`
- `Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 < 8dd4aa0122885f710930de135af2adc4ccc3238f`
- `Linux >= 38428d68719c454d269cb03b776d8a4b0ad66111 < 390b3a300d7872cef9588f003b204398be69ce08`
- `Linux 5.8`

## Remediation

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