CVE-2026-89790 is a vulnerability in Linux Kernel
Published on September 16, 2026
ipv6: avoid divide by zero in rt6_multipath_rebalance
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.
Products Associated with CVE-2026-89790
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Affected Versions
Linux:- Version bd11ff421d36abdb585b9104fa70057bf01b3110 and below f30cf8fd9872299c0c27f9916252ba2b9f422dce is affected.
- Version bd11ff421d36abdb585b9104fa70057bf01b3110 and below f82b5dbb2fef65b52a62d5ffe05e0483c4385a83 is affected.
- Version bd11ff421d36abdb585b9104fa70057bf01b3110 and below d2c26c2911dd1a363c488add4fb63eb5f0f28f87 is affected.
- Version 6.16 is affected.
- Before 6.16 is unaffected.
- Version 6.18.52, <= 6.18.* is unaffected.
- Version 7.2.6, <= 7.2.* is unaffected.
- Version 7.3-rc1, <= * is unaffected.