CVE-2026-99121Public exploit

Local denial-of-service via nexthop weight calculation race

Published Oct 28, 2026 · Updated Oct 28, 2026

Divide-by-zero in Linux IPv4 routing allows local users to trigger a kernel Oops by racing multipath route and sysctl updates. In fib_rebalance(), a concurrent ignore_routes_with_linkdown change makes nexthops eligible after their total weight was calculated as zero, which the second pass uses as a divisor. Unprivileged triggering requires access to user and network namespaces; the demonstrated consequence is a kernel task crash, not code execution.

CVSS severityUnavailable

Unscored

EPSS probability0.18%

Next 30 days · Nov 1, 2026

Known exploitationUnconfirmed

Based on sourced intelligence

Hinoki checkNot available

Coverage for this vulnerability

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Summary

What happened

The record

CVE: CVE-2026-99121
Published: Oct 28, 2026
Updated: Oct 28, 2026

Vendor: The Linux Kernel Organization
Product: Linux
Classifications: T1499.004

Attack vector: local
Privileges: authenticated

Timeline

How it unfolded

Oct 28, 2026CVE publishedPublication date reported by the CVE source.
Oct 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

Affected versionversion=0e884c78ee19e902f300ed147083c28a0c6302f0 <5046d2880fec7d49ebed2fd2866747ee1d06ad71
Affected versionversion=0e884c78ee19e902f300ed147083c28a0c6302f0 <5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f
Affected versionversion=0e884c78ee19e902f300ed147083c28a0c6302f0 <d5520e815c4b1427104ce1428ee23821f2aa824d
Affected versionversion=4.4

What conditions does exploitation require?

Attack vectorlocal

Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=0e884c78ee19e902f300ed147083c28a0c6302f0 <5046d2880fec7d49ebed2fd2866747ee1d06ad71; version=0e884c78ee19e902f300ed147083c28a0c6302f0 <5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f; version=0e884c78ee19e902f300ed147083c28a0c6302f0 <d5520e815c4b1427104ce1428ee23821f2aa824d; version=4.4

Published CVSS scores

No CVSS assessment is available in this record.

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026

Latest reporting daySep 28, 2026

Latest daily unique IPsUnavailable

Prior 30-day averageUnavailable

SourceShadowserver honeypots (KEV)

Vectorlocal

Privilegesauthenticated

Known exploitationUnconfirmed

Public exploitPublished

Weakness, pattern, technique

T1499.004Application or System Exploitation

Public exploit references

fib_rebalance local race reproducerproof of concept · demonstrated

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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