[CVE-2026-64239][MODERATE 7.0] mm/damon/sysfs-schemes: delete tried region in regions_rmdirs() [ Upstream

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

CVE: CVE-2026-64239
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: mm/damon/sysfs-schemes: delete tried region in regions_rmdirs() [ Upstream
Commit: c0e37017a452addec873865c94cf7a665663a9b2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c0e37017a452addec873865c94cf7a665663a9b2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64239
Analysis date: Fri, 24 Jul 2026 12:02:04 -0400
ActionableScore: 5
ActionableScore lower bound: 1
Actionable bucket: Actionable Moderate at minimum. Not a Strong Important candidate on current evidence
Manual review required: YES

Summary:
A DAMON sysfs lifetime bug can leave tried region objects linked after kobject_put when kobject release is delayed, causing list corruption and use-after-free during tried region refresh, with realistic impact mainly local DoS and paranoid concern for broader kernel memory corruption.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-64239 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64239

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-2026-64239	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'DAMON sysfs tried region objects can remain linked after kobject_put when the kobject release callback is delayed, leaving a stale list entry that may later be reused during tried region refresh. This creates a list corruption and use-after-free condition in mm/damon/sysfs-schemes.c. For the CVSS the PR:L is used for the paranoid score because a local process with write access to DAMON sysfs or delegated DAMON management can repeat the refresh operation, while normal host wide DAMON sysfs administration may be closer to PR:H. The issue is not network reachable and requires local interaction with the DAMON sysfs control plane. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality and integrity impact because the patch context supports a kernel use-after-free primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum. Not a Strong Important candidate on current evidence (with actual score 3)	YES	OOB UAF LINUS MEMORY  DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=5
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum. Not a Strong Important candidate on current evidence**

## 2. Signal breakdown

Conservative scoring:

* Weak or indirect memory corruption candidate: +1. The patch and commit explicitly describe list corruption and use-after-free, but no controlled reclaim, overwrite target, callback control, or type confusion is shown.
* Real lifetime corruption: +1. The bug is caused by stale lifetime handling between kobject_put(), delayed kobject release, and linked-list membership.
* Reliable kernel crash or strong DoS: +1. The reproducer shows refcount underflow and use-after-free, which can plausibly crash the kernel.
* Requires admin/root in typical deployments: -2. DAMON sysfs administration is normally root-controlled.
* Rare or non-default execution mode: -1. The commit says the issue cannot happen normally and is reproducible with CONFIG_DEBUG_KOBJECT_RELEASE.

Paranoid scoring:

* Weak or indirect memory corruption candidate: +1.
* Real lifetime corruption: +1.
* Reliable kernel crash or strong DoS: +1.
* Weak LPE concern: +1. The stale list entry and UAF occur in kernel object lifetime management, so manual review is justified even though exploit control is not demonstrated.
* Confidentiality or integrity impact plausible in worst case: +2. This is only a paranoid interpretation based on a real kernel UAF/list corruption primitive, not a demonstrated exploit.
* Rare or non-default execution mode: -1.

Paranoid total: 5.

## 3. Reachability analysis

The trigger is local through the DAMON sysfs control plane, specifically repeated refresh of DAMOS tried region directories. In normal deployments this interface is typically writable only by root or an administrator-level process, so the conservative privilege interpretation is high. A lower-privilege interpretation is possible only if DAMON management is delegated to a service, container root, or constrained local account with write access to the relevant sysfs paths.

The path is not network reachable. The commit also states that the issue should not occur in normal situations because the kobject release delay needed for reproduction is associated with CONFIG_DEBUG_KOBJECT_RELEASE, which is not a typical production configuration.

## 4. Severity interpretation

This is not an ordinary pure DoS cleanup bug because the patch fixes a real lifetime/list corruption condition and the commit explicitly mentions use-after-free. However, the practical exploitability is limited by root-controlled DAMON sysfs access and the non-default CONFIG_DEBUG_KOBJECT_RELEASE dependency.

Realistically this behaves like a low-to-moderate local DoS in typical production configurations. Paranoid triage should keep it as Actionable Moderate because kernel UAF/list corruption exists and should not be auto-closed without manual review.

## 5. One-sentence report phrase

A DAMON sysfs lifetime bug can leave tried region objects linked after kobject_put when kobject release is delayed, causing list corruption and use-after-free during tried region refresh, with realistic impact mainly local DoS and paranoid concern for broader kernel memory corruption.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the normal triggerability is limited, but the bug class is real kernel UAF/list corruption in object lifetime management, so it should not be auto-closed solely as a low-risk debug-configuration issue.

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

Patch: mm/damon/sysfs-schemes: delete tried region in regions_rmdirs() [ Upstream
Commit: c0e37017a452addec873865c94cf7a665663a9b2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c0e37017a452addec873865c94cf7a665663a9b2

Changed files:
  mm/damon/sysfs-schemes.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=c0e37017a452addec873865c94cf7a665663a9b2

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

The original Linux kernel CVE announcement for CVE-2026-64239 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64239

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:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 1
  Paranoid ActionableScore: 5

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: NO
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).