---
id: CVE-2026-89790
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ipv6: avoid divide by zero in rt6_multipath_rebalance

  rt6_multipath_rebalance() calculates the total eligible nexthop weight
  in one pass and programs upper bounds in a…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  ipv6: avoid divide by zero in rt6_multipath_rebalance

  rt6_multipath_rebalance() calculates the total eligible nexthop weight
  in one pass and programs upper bounds in a…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= bd11ff421d36abdb585b9104fa70057bf01b3110 <
    f30cf8fd9872299c0c27f9916252ba2b9f422dce
  - >-
    Linux >= bd11ff421d36abdb585b9104fa70057bf01b3110 <
    f82b5dbb2fef65b52a62d5ffe05e0483c4385a83
  - >-
    Linux >= bd11ff421d36abdb585b9104fa70057bf01b3110 <
    d2c26c2911dd1a363c488add4fb63eb5f0f28f87
  - Linux 6.16
published: '2026-09-16'
updated: '2026-09-16'
sourceUpdated: '2026-09-16T09:17:09.827'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89790'
references:
  - url: 'https://git.kernel.org/stable/c/d2c26c2911dd1a363c488add4fb63eb5f0f28f87'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f30cf8fd9872299c0c27f9916252ba2b9f422dce'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/f82b5dbb2fef65b52a62d5ffe05e0483c4385a83'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-16T08:52:29.591Z'
epss: 0.00206
epssPercentile: 0.09424
---

## Overview

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

ipv6: avoid divide by zero in rt6_multipath_rebalance

rt6_multipath_rebalance() calculates the total eligible nexthop weight
in one pass and programs upper bounds in a second pass. Since
RTM_NEWROUTE is RTNL-free, a concurrent
ignore_routes_with_linkdown update can make the first pass return zero
while the second sees an eligible nexthop, causing
rt6_upper_bound_set() to divide by zero.

UBSAN: division-overflow in net/ipv6/route.c:4845:17
Oops: divide error: 0000 [#1] SMP KASAN NOPTI
  rt6_upper_bound_set() net/ipv6/route.c:4845
  rt6_multipath_rebalance()
  fib6_add_rt2node()
  ip6_route_multipath_add()
  inet6_rtm_newroute()

Skip upper-bound calculation when the first pass reports a zero total.
This respects the lock-free performance considerations here and solves
insecure scenarios.

## Remediation

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