CVE-2026-99071

Kernel warning via route-notification sizing race

Published Oct 23, 2026 · Updated Oct 23, 2026

Linux Kernel IPv4 route notifications allow attackers to trigger a spurious kernel warning during concurrent nexthop replacement. In fib_alias_hw_flags_set(), fib_nlmsg_size() and fib_dump_info() observe different group sizes, and WARN_ON incorrectly treats the resulting -EMSGSIZE as a bug. Nexthop compatibility mode and concurrent group growth during hardware-flag notification are required; with panic_on_warn enabled, the warning causes a kernel panic.

CVSS severityUnavailable
Unscored
EPSS probability0.21%
Next 30 days · Nov 1, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Linux Kernel IPv4 route notifications allow attackers to trigger a spurious kernel warning during concurrent nexthop replacement. In fib_alias_hw_flags_set(), fib_nlmsg_size() and fib_dump_info() observe different group sizes, and WARN_ON incorrectly treats the resulting -EMSGSIZE as a bug. Nexthop compatibility mode and concurrent group growth during hardware-flag notification are required; with panic_on_warn enabled, the warning causes a kernel panic.

The record

CVE
CVE-2026-99071
Published
Oct 23, 2026
Updated
Oct 23, 2026
Vendor
Linux Foundation
Product
Linux Kernel
Classifications
Unavailable
Attack vector
Unavailable
Privileges
Unavailable

Timeline

How it unfolded

  1. Oct 23, 2026CVE publishedPublication date reported by the CVE source.
  2. Oct 23, 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.

  1. Affected versionversion=5.12
  2. Affected versionversion=680aea08e78c003292415518ad270bc20f9c80b1 <088ba80eef85fa7a5ad8f9e7c82b403c99242b56
  3. Affected versionversion=680aea08e78c003292415518ad270bc20f9c80b1 <221ef5e1e44a044790f0f54e6aa237883f475a4d
  4. Affected versionversion=680aea08e78c003292415518ad270bc20f9c80b1 <78a1cf5c54b2f795c81fedb530755a8d01cc84f0
  5. Affected versionversion=680aea08e78c003292415518ad270bc20f9c80b1 <7dfa7ca97f3ac46353edd4cc44f7733758e4535b
  6. Affected versionversion=680aea08e78c003292415518ad270bc20f9c80b1 <e02a5b6588161673ef75a4bc5cdfb62bd493374d

What conditions does exploitation require?

Attack vectorUnavailable in this record.
Required privilegesUnavailable in this record.

What is affected?

Linux Foundation · Linux Kernelversion=5.12; version=680aea08e78c003292415518ad270bc20f9c80b1 <088ba80eef85fa7a5ad8f9e7c82b403c99242b56; version=680aea08e78c003292415518ad270bc20f9c80b1 <221ef5e1e44a044790f0f54e6aa237883f475a4d; version=680aea08e78c003292415518ad270bc20f9c80b1 <78a1cf5c54b2f795c81fedb530755a8d01cc84f0; version=680aea08e78c003292415518ad270bc20f9c80b1 <7dfa7ca97f3ac46353edd4cc44f7733758e4535b; version=680aea08e78c003292415518ad270bc20f9c80b1 <e02a5b6588161673ef75a4bc5cdfb62bd493374d

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)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

Public exploit references

No public exploit references are available in this record.

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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