---
id: CVE-2023-53477
title: 'ipv6: Add lwtunnel encap size of all siblings in nexthop calculation'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ipv6: Add lwtunnel encap size of all siblings in nexthop calculation

  In function rt6_nlmsg_size(), the length of nexthop is calculated
  by multipling the nexthop length…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= beb1afac518dec5a15dc92ba8f0ca016dcf457b4 <
    aba298b35619213ca787d08d472049627d8cd012
  - >-
    Linux >= beb1afac518dec5a15dc92ba8f0ca016dcf457b4 <
    da26369377f0b671c14692e2d65ceb38131053e1
  - >-
    Linux >= beb1afac518dec5a15dc92ba8f0ca016dcf457b4 <
    dcdddb5f490890d058ea1f194d661219e92fe88d
  - >-
    Linux >= beb1afac518dec5a15dc92ba8f0ca016dcf457b4 <
    e11e4d524eba2d3c8fdf897d7ce3853f7573bae9
  - >-
    Linux >= beb1afac518dec5a15dc92ba8f0ca016dcf457b4 <
    aa75d826c221e8d48607aef33836cf872a159cf1
  - >-
    Linux >= beb1afac518dec5a15dc92ba8f0ca016dcf457b4 <
    4cc59f386991ec9374cb4bc83dbe1c0b5a95033f
  - Linux 4.11
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-11-05T20:21:59.010628Z'
published: '2025-10-01'
updated: '2026-11-05'
sourceUpdated: '2026-11-05T20:31:11.115Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2023-53477'
references:
  - url: 'https://git.kernel.org/stable/c/aba298b35619213ca787d08d472049627d8cd012'
  - url: 'https://git.kernel.org/stable/c/da26369377f0b671c14692e2d65ceb38131053e1'
  - url: 'https://git.kernel.org/stable/c/dcdddb5f490890d058ea1f194d661219e92fe88d'
  - url: 'https://git.kernel.org/stable/c/e11e4d524eba2d3c8fdf897d7ce3853f7573bae9'
  - url: 'https://git.kernel.org/stable/c/aa75d826c221e8d48607aef33836cf872a159cf1'
  - url: 'https://git.kernel.org/stable/c/4cc59f386991ec9374cb4bc83dbe1c0b5a95033f'
tags:
  - cve.org
epss: 0.0016
epssPercentile: 0.05153
ingestedAt: '2026-11-05T22:38:31.800Z'
---

## Overview

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

ipv6: Add lwtunnel encap size of all siblings in nexthop calculation

In function rt6_nlmsg_size(), the length of nexthop is calculated
by multipling the nexthop length of fib6_info and the number of
siblings. However if the fib6_info has no lwtunnel but the siblings
have lwtunnels, the nexthop length is less than it should be, and
it will trigger a warning in inet6_rt_notify() as follows:

WARNING: CPU: 0 PID: 6082 at net/ipv6/route.c:6180 inet6_rt_notify+0x120/0x130
......
Call Trace:
 <TASK>
 fib6_add_rt2node+0x685/0xa30
 fib6_add+0x96/0x1b0
 ip6_route_add+0x50/0xd0
 inet6_rtm_newroute+0x97/0xa0
 rtnetlink_rcv_msg+0x156/0x3d0
 netlink_rcv_skb+0x5a/0x110
 netlink_unicast+0x246/0x350
 netlink_sendmsg+0x250/0x4c0
 sock_sendmsg+0x66/0x70
 ___sys_sendmsg+0x7c/0xd0
 __sys_sendmsg+0x5d/0xb0
 do_syscall_64+0x3f/0x90
 entry_SYSCALL_64_after_hwframe+0x72/0xdc

This bug can be reproduced by script:

ip -6 addr add 2002::2/64 dev ens2
ip -6 route add 100::/64 via 2002::1 dev ens2 metric 100

for i in 10 20 30 40 50 60 70;
do
	ip link add link ens2 name ipv_$i type ipvlan
	ip -6 addr add 2002::$i/64 dev ipv_$i
	ifconfig ipv_$i up
done

for i in 10 20 30 40 50 60;
do
	ip -6 route append 100::/64 encap ip6 dst 2002::$i via 2002::1
dev ipv_$i metric 100
done

ip -6 route append 100::/64 via 2002::1 dev ipv_70 metric 100

This patch fixes it by adding nexthop_len of every siblings using
rt6_nh_nlmsg_size().

## Affected

- `Linux >= beb1afac518dec5a15dc92ba8f0ca016dcf457b4 < aba298b35619213ca787d08d472049627d8cd012`
- `Linux >= beb1afac518dec5a15dc92ba8f0ca016dcf457b4 < da26369377f0b671c14692e2d65ceb38131053e1`
- `Linux >= beb1afac518dec5a15dc92ba8f0ca016dcf457b4 < dcdddb5f490890d058ea1f194d661219e92fe88d`
- `Linux >= beb1afac518dec5a15dc92ba8f0ca016dcf457b4 < e11e4d524eba2d3c8fdf897d7ce3853f7573bae9`
- `Linux >= beb1afac518dec5a15dc92ba8f0ca016dcf457b4 < aa75d826c221e8d48607aef33836cf872a159cf1`
- `Linux >= beb1afac518dec5a15dc92ba8f0ca016dcf457b4 < 4cc59f386991ec9374cb4bc83dbe1c0b5a95033f`
- `Linux 4.11`

## Remediation

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