ipv6: avoid divide by zero in rt6_multipath_rebalance (CVE-2026-89790) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-89790

ipv6: avoid divide by zero in rt6_multipath_rebalance

Answer in brief

CVE-2026-89790 records a Unknown severity vulnerability in ipv6: avoid divide by zero in rt6_multipath_rebalance. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 16, 2026Updated Sep 16, 2026Source checked Sep 16, 2026First seen by HOL Sep 16, 2026Material review Sep 16, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Linux/Linuxgeneric	>=bd11ff421d36abdb585b9104fa70057bf01b3110 <f30cf8fd9872299c0c27f9916252ba2b9f422dce \|\| >=bd11ff421d36abdb585b9104fa70057bf01b3110 <f82b5dbb2fef65b52a62d5ffe05e0483c4385a83 \|\| >=bd11ff421d36abdb585b9104fa70057bf01b3110 <d2c26c2911dd1a363c488add4fb63eb5f0f28f87	f30cf8fd9872299c0c27f9916252ba2b9f422dce, f82b5dbb2fef65b52a62d5ffe05e0483c4385a83, d2c26c2911dd1a363c488add4fb63eb5f0f28f87
Linux/Linuxgeneric	6.16	Not reported

Recommended response

Check inventory. Check lockfiles and deployed manifests for Linux/Linux, Linux/Linux.
Review the reported fix. Update Linux/Linux to f30cf8fd9872299c0c27f9916252ba2b9f422dce if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 16, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 16, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 16, 2026

Sources and claim methodology

Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.