---
id: CVE-2026-23300
title: 'net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop

  When a standalone IPv6 nexthop object is created with a loopback device
  (e.g., "ip -6 nexthop add…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e <
    607e68c1b7c5a30c795571be1906d716e989a644
  - >-
    Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e <
    c11d7c56c2076ee9cd72004f1976fe0734df2ae9
  - >-
    Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e <
    b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a
  - >-
    Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e <
    b299121e7453d23faddf464087dff513a495b4fc
  - >-
    Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e <
    f7c9f8e3607440fe39300efbaf46cf7b5eecb23f
  - >-
    Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e <
    b3b5a037d520afe3d5276e653bc0ff516bbda34c
  - >-
    Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e <
    8650db85b4259d2885d2a80fbc2317ce24194133
  - >-
    Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e <
    21ec92774d1536f71bdc90b0e3d052eff99cf093
  - Linux 5.3
published: '2026-03-25'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T08:45:31.317Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-23300'
references:
  - url: 'https://git.kernel.org/stable/c/607e68c1b7c5a30c795571be1906d716e989a644'
  - url: 'https://git.kernel.org/stable/c/c11d7c56c2076ee9cd72004f1976fe0734df2ae9'
  - url: 'https://git.kernel.org/stable/c/b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a'
  - url: 'https://git.kernel.org/stable/c/b299121e7453d23faddf464087dff513a495b4fc'
  - url: 'https://git.kernel.org/stable/c/f7c9f8e3607440fe39300efbaf46cf7b5eecb23f'
  - url: 'https://git.kernel.org/stable/c/b3b5a037d520afe3d5276e653bc0ff516bbda34c'
  - url: 'https://git.kernel.org/stable/c/8650db85b4259d2885d2a80fbc2317ce24194133'
  - url: 'https://git.kernel.org/stable/c/21ec92774d1536f71bdc90b0e3d052eff99cf093'
tags:
  - cve.org
epss: 0.00129
epssPercentile: 0.02086
ingestedAt: '2026-09-08T15:33:26.993Z'
---

## Overview

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

net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop

When a standalone IPv6 nexthop object is created with a loopback device
(e.g., "ip -6 nexthop add id 100 dev lo"), fib6_nh_init() misclassifies
it as a reject route. This is because nexthop objects have no destination
prefix (fc_dst=::), causing fib6_is_reject() to match any loopback
nexthop. The reject path skips fib_nh_common_init(), leaving
nhc_pcpu_rth_output unallocated. If an IPv4 route later references this
nexthop, __mkroute_output() dereferences NULL nhc_pcpu_rth_output and
panics.

Simplify the check in fib6_nh_init() to only match explicit reject
routes (RTF_REJECT) instead of using fib6_is_reject(). The loopback
promotion heuristic in fib6_is_reject() is handled separately by
ip6_route_info_create_nh(). After this change, the three cases behave
as follows:

1. Explicit reject route ("ip -6 route add unreachable 2001:db8::/64"):
   RTF_REJECT is set, enters reject path, skips fib_nh_common_init().
   No behavior change.

2. Implicit loopback reject route ("ip -6 route add 2001:db8::/32 dev lo"):
   RTF_REJECT is not set, takes normal path, fib_nh_common_init() is
   called. ip6_route_info_create_nh() still promotes it to reject
   afterward. nhc_pcpu_rth_output is allocated but unused, which is
   harmless.

3. Standalone nexthop object ("ip -6 nexthop add id 100 dev lo"):
   RTF_REJECT is not set, takes normal path, fib_nh_common_init() is
   called. nhc_pcpu_rth_output is properly allocated, fixing the crash
   when IPv4 routes reference this nexthop.

## Affected

- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < 607e68c1b7c5a30c795571be1906d716e989a644`
- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < c11d7c56c2076ee9cd72004f1976fe0734df2ae9`
- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a`
- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < b299121e7453d23faddf464087dff513a495b4fc`
- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < f7c9f8e3607440fe39300efbaf46cf7b5eecb23f`
- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < b3b5a037d520afe3d5276e653bc0ff516bbda34c`
- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < 8650db85b4259d2885d2a80fbc2317ce24194133`
- `Linux >= 493ced1ac47c48bb86d9d4e8e87df8592be85a0e < 21ec92774d1536f71bdc90b0e3d052eff99cf093`
- `Linux 5.3`

## Remediation

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