[CVE-2026-64372][MODERATE 7.0] cpufreq: pcc: fix use-after-free and double free in _OSC evaluation

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

CVE: CVE-2026-64372
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: cpufreq: pcc: fix use-after-free and double free in _OSC evaluation
Commit: 8e454e9d0bc03446d610ee49abec9dfd424f6541
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8e454e9d0bc03446d610ee49abec9dfd424f6541
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64372
Analysis date: Sat, 25 Jul 2026 09:43:56 -0400
ActionableScore: 6
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A stale ACPI output buffer in `pcc_cpufreq_do_osc()` can cause a use-after-free write and double free during two-phase `_OSC` negotiation, leading to kernel memory corruption and likely local DoS, with privilege escalation only a paranoid concern due to the privileged and firmware-mediated trigger path.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64372 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64372

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-2026-64372	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-415;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '6.4';DESCR 'pcc_cpufreq_do_osc() can hit a use-after-free write and a double free during the two phase ACPI _OSC negotiation. The first acpi_evaluate_object() result is freed, but output.pointer and output.length remain in a state that makes the second acpi_evaluate_object() treat the freed pointer as a reusable output buffer. This can corrupt freed kernel heap memory and the later cleanup can free the same pointer again. For the CVSS the PR:H is used because reliable triggering normally requires administrative control over driver loading or the boot and ACPI environment, not just an unprivileged local user. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	LOCK DANGER UAF HARDWARE KPANIC 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Generic memory corruption: +2. The bug is an explicit use-after-free write followed by double free of the same ACPI output buffer.
* Real lifetime corruption: +1. The stale `output.pointer` remains live after `kfree()` and is reused by the second `acpi_evaluate_object()` call.
* Reliable kernel crash / strong DoS: +1. UAF write plus double free in kernel heap can realistically crash the kernel.
* Firmware-mediated external influence: +1. The data path depends on ACPI `_OSC` evaluation and platform firmware behavior, but it is not directly network reachable.
* Privileged kernel/device-management memory corruption path: +1. The corruption occurs during cpufreq PCC driver initialization in a trusted ACPI/device-management path.
* Requires admin/root/boot or ACPI control in typical deployments: -2. Reliable triggering normally requires host administrative control, module/driver initialization control, or firmware/ACPI influence.
* Conservative total: 4.

Paranoid additions:

* Confidentiality impact plausible: +1. Kernel heap UAF/double-free can theoretically expose or influence adjacent kernel objects, although no leak primitive is shown.
* Integrity impact plausible: +1. The second `_OSC` result may be written into freed heap memory, so limited kernel memory corruption is technically plausible.
* Paranoid total: 6.

Not awarded:

* Remote reachable: +0. No network path is involved.
* Local unprivileged trigger: +0. No evidence that an unprivileged local user can directly trigger this path.
* Strong LPE plausibility: +0. The patch shows UAF write and double free, but not attacker-controlled reclaim, callback control, arbitrary write, or reliable object replacement.

## 3. Reachability analysis

The vulnerable function is `pcc_cpufreq_do_osc()` in the PCC cpufreq driver and is marked `__init`, so the main trigger is driver initialization or boot-time probing on systems with the relevant ACPI PCC interface. A normal unprivileged local user is not expected to reach this path directly. Containers and namespaces generally do not reduce the privilege requirement because ACPI firmware state and host driver initialization are outside ordinary container control. Realistic triggering requires a matching platform, driver load or boot path, and potentially influence over ACPI `_OSC` responses through firmware or platform configuration.

Call-site confidence: medium. The provided patch and commit message clearly identify the two `acpi_evaluate_object()` calls and the stale output buffer lifetime, but full surrounding call paths and platform probing logic are not included.

## 4. Severity interpretation

This is stronger than an ordinary Moderate correctness fix because the commit explicitly describes kernel heap use-after-free and double free. However, the realistic attack surface is narrow because the trigger is tied to privileged driver initialization and ACPI firmware/platform behavior, not a common unprivileged syscall or network parser. Conservative handling is Borderline to Actionable Moderate. Paranoid handling reaches Actionable Moderate because kernel memory corruption is real and manual review is warranted, but the evidence does not justify treating it as a strong Important candidate without a demonstrated reclaim or privilege-escalation path.

## 5. One-sentence report phrase

A stale ACPI output buffer in `pcc_cpufreq_do_osc()` can cause a use-after-free write and double free during two-phase `_OSC` negotiation, leading to kernel memory corruption and likely local DoS, with privilege escalation only a paranoid concern due to the privileged and firmware-mediated trigger path.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Explicit UAF write and double free in kernel heap should not be auto-closed, even though practical reachability appears limited to privileged driver initialization or firmware-mediated conditions.

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UPSTREAM PATCH SUMMARY
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Patch: cpufreq: pcc: fix use-after-free and double free in _OSC evaluation
Commit: 8e454e9d0bc03446d610ee49abec9dfd424f6541
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8e454e9d0bc03446d610ee49abec9dfd424f6541

Commit description:

pcc_cpufreq_do_osc() calls acpi_evaluate_object() twice for the
two-phase _OSC negotiation. Between the two calls it freed
output.pointer but left output.length unchanged. Since
acpi_evaluate_object() treats a non-zero length with a non-NULL
pointer as an existing buffer to write into, the second call wrote
into freed memory (use-after-free). The subsequent kfree(output.pointer)
at out_free then freed the same pointer a second time (double free).

Reset output.pointer to NULL and output.length to ACPI_ALLOCATE_BUFFER
after freeing the first result, so ACPICA allocates a fresh buffer for
each phase independently.

Fixes: 0f1d683 ("[CPUFREQ] Processor Clocking Control interface driver")
Signed-off-by: Yuho Choi <dbgh9129@gmail.com>
Reviewed-by: Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>
Cc: All applicable <stable@vger.kernel.org>
Link: https://patch.msgid.link/20260416144621.93964-1-dbgh9129@gmail.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/cpufreq/pcc-cpufreq.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=8e454e9d0bc03446d610ee49abec9dfd424f6541

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

The original Linux kernel CVE announcement for CVE-2026-64372 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64372

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:H/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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: 4
  Paranoid ActionableScore: 6

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).