[CVE-2026-64185][LOW] sysfs: don't remove existing directory on update failure

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

CVE: CVE-2026-64185
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: sysfs: don't remove existing directory on update failure
Commit: c5e125c828b701afaf7493b42a14aa89362ff36d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c5e125c828b701afaf7493b42a14aa89362ff36d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64185
Analysis date: Sun, 19 Jul 2026 13:53:40 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A sysfs named group update failure can incorrectly remove an existing sysfs directory, causing local control-plane degradation or availability impact without evidence of memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-64185 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64185

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: LOW
Manual review required: NO

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

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-64185	LOW	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:L/UI:N/S:U/C:N/I:L/A:H';CWE-703;CWE-754;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.3';DESCR 'A sysfs named group update can incorrectly remove an already existing directory when create_files() fails during sysfs_update_group(). This can silently destroy a sysfs interface that the caller did not create and may break device or subsystem management until a retry, reload, or recovery path restores it. For the CVSS the PR:L is used because practical triggering requires a local process or user context that can influence the relevant update path or resource pressure, even if no full administrator privilege is necessarily required. The issue is not network reachable and does not provide a demonstrated memory corruption primitive. Impact is mainly local denial of service and limited integrity impact on the sysfs control plane.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	DISK SIMPLEFIX LINUS  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Triggered signals:

* Broad/default/common subsystem exposure: +1
  sysfs is a core kernel control-plane filesystem and widely present.

* Availability impact realistic: +1
  A failed update can silently remove an existing sysfs group, potentially breaking device or subsystem management until retry, reload, or recovery.

Not triggered:

* No generic memory corruption. The patch shows a logic/error-path bug, not UAF, OOB, double-free, refcount misuse, or type confusion.
* No privilege escalation plausible. There is no shown primitive for controlled overwrite, object replacement, callback control, or credential/security-boundary manipulation.
* No remote/network trigger. The affected path is sysfs group update logic, not packet processing or remote protocol parsing.
* No strong DoS point. The issue can break a sysfs interface, but the patch does not show reliable kernel crash, panic, or system-wide lockup.
* Local unprivileged trigger is not counted. A local user may contribute to memory pressure, but reliable triggering also needs a kernel subsystem to call sysfs_update_group() on a named group and hit create_files() failure.

Subtractions considered:

* Hard/special condition: effectively offsets any weak local-trigger concern. The bug needs an update path plus create_files() failure such as ENOMEM.

## 3. Reachability analysis

The bug is triggered when kernel code calls sysfs_update_group() for a named group and create_files() fails. The existing directory was found through kernfs_find_and_get(), so removing it on failure destroys a sysfs group that existed before the update attempt.

A normal local user cannot directly call internal_create_group(). Practical triggering likely requires an indirect subsystem path plus memory pressure or another failure condition. Namespaces and containers do not obviously make this a strong unprivileged primitive, although containerized workloads might contribute to resource pressure depending on limits. The path is not network reachable.

Call-site confidence: medium. The changed function and error path are visible, but specific subsystem callers are not included in the patch input.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like reliability/control-plane issue, not an Important-class kernel vulnerability. The realistic impact is loss or degradation of a sysfs management interface after an update failure. Theoretical impact can include limited integrity degradation of the sysfs control plane and local availability impact, but there is no evidence of memory corruption, privilege escalation, information disclosure, or a persistent system-wide failure.

## 5. One-sentence report phrase

A sysfs named group update failure can incorrectly remove an existing sysfs directory, causing local control-plane degradation or availability impact without evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a narrow sysfs error-path logic bug with no demonstrated memory corruption, no network reachability, no privilege escalation primitive, and only limited local availability or control-plane integrity impact.

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

Patch: sysfs: don't remove existing directory on update failure
Commit: c5e125c828b701afaf7493b42a14aa89362ff36d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c5e125c828b701afaf7493b42a14aa89362ff36d

Commit description:

When sysfs_update_group() is called for a named group and create_files()
fails (e.g. -ENOMEM), internal_create_group() calls kernfs_remove(kn) on
the group directory.  In the update path, kn was obtained via
kernfs_find_and_get() and refers to a directory that already existed
before this call.  Removing it silently destroys a sysfs group that the
caller did not create.

Only remove the directory if we created it ourselves.  On update failure
the directory remains as it is left empty by remove_files() inside
create_files(), but can be repopulated by a retry.

Cc: Rajat Jain <rajatja@google.com>
Fixes: c855cf2 ("sysfs: Fix internal_create_group() for named group updates")
Cc: stable <stable@kernel.org>
Assisted-by: gkh_clanker_t1000
Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/2026052003-uniquely-hastily-c093@gregkh
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/sysfs/group.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=c5e125c828b701afaf7493b42a14aa89362ff36d

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

The original Linux kernel CVE announcement for CVE-2026-64185 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64185

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:N/I:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS score: 5.3

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: unknown
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).