[CVE-2026-72066][MODERATE 7.0] cpu: hotplug: Bound hotplug states sysfs output

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-72066
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: cpu: hotplug: Bound hotplug states sysfs output
Commit: 2408be459c70ef4250da1a9e50f5478e6b250d61
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2408be459c70ef4250da1a9e50f5478e6b250d61
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72066
Analysis date: Sat, 15 Aug 2026 20:47:30 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A local read of the CPU hotplug states sysfs file can cause states_show() to append enough state names with unbounded sprintf() to write past the PAGE_SIZE sysfs buffer, leading to kernel memory corruption and possible crash, with privilege escalation not proven but requiring manual review.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-72066 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72066

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: MODERATE 7.0
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-72066	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-120;CWE-119;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'A kernel out-of-bounds write can occur in the CPU hotplug sysfs states_show handler because it appends state names into a PAGE_SIZE sysfs buffer with sprintf without checking the remaining space. If enough CPU hotplug states are registered, reading the sysfs state file can write past the end of the buffer and corrupt adjacent kernel memory. For the CVSS the PR:L is used because a local process is required to trigger the vulnerable sysfs read path, even if the file is readable by an unprivileged user. The issue is not network reachable and requires local access to the target system. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality or integrity impact because the primitive is a kernel out-of-bounds write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	DANGER SIMPLEFIX HARDWARE LINUS KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. The vulnerable path is a sysfs show handler and can likely be triggered by a local read of the CPU hotplug states file.
* Constrained kernel buffer overwrite: +1. The bug is an out-of-bounds write past the PAGE_SIZE sysfs buffer, but the written data is mostly kernel-derived state numbers and names rather than an attacker-controlled payload.
* Reliable kernel crash / strong DoS: +1. Writing past a sysfs buffer in kernel context can corrupt adjacent memory and plausibly crash the kernel.
* Broad/default/common subsystem: +1. CPU hotplug and sysfs are core kernel facilities, not a rare driver-only path.
* Integrity impact plausible: +1. The primitive is a kernel OOB write, so adjacent kernel memory corruption is plausible even if target control is not demonstrated.

Paranoid additional signals:

* Upgrade constrained overwrite to generic memory corruption: +1 net. In the paranoid view, this is still a real kernel OOB write primitive, not merely a warning or validation issue.
* Weak LPE concern: +1. Privilege escalation is not demonstrated, but kernel memory corruption from an unprivileged read path is enough to require manual review.

Not counted:

* Remote reachable: +0. No network trigger is indicated.
* Strong LPE plausibility: +0. No controlled overwrite target, reclaim primitive, type confusion, callback control, or arbitrary write is shown.
* Confidentiality impact: +0 in ActionableScore. There is no direct readback or information disclosure primitive.

## 3. Reachability analysis

A local process can trigger the vulnerable function by reading the CPU hotplug states sysfs attribute. The attacker likely cannot control the registered CPU hotplug state names directly, so the overflow depends on the kernel configuration and the number of registered named states. Namespaces and containers may matter if host sysfs is exposed into a container, but in typical hardened container setups sysfs is restricted or read-only. The path is not network reachable and does not require packet input. Call-site confidence: high, because the patch directly shows the sysfs show function and the unsafe sprintf loop.

## 4. Severity interpretation

This is not an ordinary Low or simple Moderate issue because the patch fixes a concrete kernel out-of-bounds write. Realistic exploitation is limited by the lack of obvious attacker-controlled payload and target selection, so the conservative interpretation is Actionable Moderate. The paranoid interpretation reaches Strong Important candidate because the trigger may be local unprivileged and the primitive is kernel memory corruption, which historically deserves manual review even when exploitability is not proven.

## 5. One-sentence report phrase

A local read of the CPU hotplug states sysfs file can cause states_show() to append enough state names with unbounded sprintf() to write past the PAGE_SIZE sysfs buffer, leading to kernel memory corruption and possible crash, with privilege escalation not proven but requiring manual review.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug is a real kernel OOB write reachable from a local sysfs read path. The payload appears constrained and kernel-derived, but the memory corruption class and possible unprivileged trigger make auto-closure unsafe.

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UPSTREAM PATCH SUMMARY
======================================================================

Patch: cpu: hotplug: Bound hotplug states sysfs output
Commit: 2408be459c70ef4250da1a9e50f5478e6b250d61
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2408be459c70ef4250da1a9e50f5478e6b250d61

Commit description:

states_show() adds CPU hotplug state names into a single sysfs buffer
using sprintf(). With enough registered states, this can write past the
end of the PAGE_SIZE buffer.

Use sysfs_emit_at() so output is bounded.

Fixes: 98f8cdc ("cpu/hotplug: Add sysfs state interface")
Signed-off-by: Bradley Morgan <include@grrlz.net>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260619163719.12103-2-include@grrlz.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/cpu.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2408be459c70ef4250da1a9e50f5478e6b250d61

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DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-72066 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72066

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: 5
  Paranoid ActionableScore: 7

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: MODERATE
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): MODERATE 7.0

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).