[CVE-2026-74330][MODERATE 7.0] configfs: fix lockless traversals of ->s_children [ Upstream

[CVE-2026-74330][MODERATE 7.0] configfs: fix lockless traversals of ->s_children [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74330
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: configfs: fix lockless traversals of ->s_children [ Upstream
Commit: 77fd6f50f633a52c2db061e7d71d8cb486b0265e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=77fd6f50f633a52c2db061e7d71d8cb486b0265e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74330
Analysis date: Sat, 15 Aug 2026 18:34:53 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A configfs race allowed lockless traversal of `s_children` while directory cursor entries could be moved by `lseek()` or freed concurrently, creating a local use-after-free candidate with realistic kernel crash impact and possible but unproven privilege-escalation relevance.

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

The original Linux kernel CVE announcement for CVE-2026-74330 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74330

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
======================================================================

CVE-2026-74330	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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-362;*CWE-416;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'configfs had lockless traversal of the s_children list while directory cursor entries could be moved by lseek or freed concurrently. This creates a race condition and a use-after-free candidate in kernel list traversal, with realistic impact of a local denial of service through crash or list corruption. For the CVSS the PR:L is used for the paranoid score because a local process may participate through directory cursor operations while configfs objects are removed or detached, although reliable triggering depends on permissions and timing. The issue is not network reachable and requires local interaction with configfs. Impact is at least local denial of service and in the worst defensible case may allow confidentiality or integrity impact due to kernel memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)	YES	LOCK DISK LINUS  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Memory corruption, weak/indirect corruption candidate: +1. The patch fixes lockless traversal of `s_children` where cursor entries may be moved or freed concurrently.
* Real lifetime corruption: +1. The commit explicitly mentions cursors can be freed while traversal is ongoing.
* Reliable kernel crash / strong DoS: +1. A stale list entry or freed cursor in kernel list traversal can plausibly crash the kernel.
* Hard or unreliable race / special timing required: -1. Triggering depends on concurrent traversal, lseek cursor movement, and detach/removal paths.
* Requires admin/root/CAP_* in typical deployments: -2. Creating/removing many configfs objects is normally privileged.

Paranoid signals:

* Local unprivileged trigger: +1. A local process may participate through directory cursor operations such as `lseek()` if it can open affected configfs directories.
* Memory corruption, weak/indirect corruption candidate: +1. The primitive is a lockless list traversal over entries that may include freed or moved cursor objects.
* Real lifetime corruption: +1. This is a concrete lifetime race involving cursor objects.
* Weak LPE concern: +1. The affected code walks kernel objects and may act on stale or misinterpreted list entries, but no controlled reclaim or overwrite primitive is shown.
* Reliable kernel crash / strong DoS: +1. Kernel crash or list corruption is a realistic outcome.
* Broad/default/common subsystem or ordinary local interface: +1. configfs is a common kernel pseudo-filesystem interface, though not always mounted or writable by unprivileged users.
* Hard or unreliable race / special timing required: -1. Race timing remains a meaningful limiting factor.

Call-site confidence: high. The patch shows the affected traversal sites and the added locking directly.

## 3. Reachability analysis

The bug is local, not network reachable. In typical deployments, meaningful configfs object creation, deletion, and detach operations require root or administrative capabilities. However, the cursor side of the race can involve ordinary directory iteration and `lseek()` behavior, so reduced-privilege or containerized environments with exposed configfs access deserve manual review.

The path is not a packet-processing or remote protocol path. Exploitation requires local interaction with configfs and a concurrent teardown or detach path. The realistic impact is kernel crash or corrupted configfs traversal state. A privilege-escalation path is not demonstrated, but the lifetime race is serious enough to avoid automatic closure.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is not just a validation bug or resource leak. It is a race involving possible use-after-free of configfs cursor/list objects.

Realistically, the strongest supported impact is local DoS via kernel crash. Theoretical confidentiality or integrity impact is possible only as a paranoid interpretation of kernel memory corruption, because the patch does not show controlled reclaim, arbitrary write, callback control, or type confusion. Therefore this is best treated as Actionable Moderate at minimum, with manual review required before downgrading.

## 5. One-sentence report phrase

A configfs race allowed lockless traversal of `s_children` while directory cursor entries could be moved by `lseek()` or freed concurrently, creating a local use-after-free candidate with realistic kernel crash impact and possible but unproven privilege-escalation relevance.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug is a kernel lifetime race with possible UAF behavior in list traversal. Even though realistic exploitation appears to be local DoS and likely requires privileged configfs manipulation, the cursor lifetime aspect makes it unsafe to auto-close without manual source review.

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

Patch: configfs: fix lockless traversals of ->s_children [ Upstream
Commit: 77fd6f50f633a52c2db061e7d71d8cb486b0265e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=77fd6f50f633a52c2db061e7d71d8cb486b0265e

Changed files:
  fs/configfs/dir.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=77fd6f50f633a52c2db061e7d71d8cb486b0265e

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

The original Linux kernel CVE announcement for CVE-2026-74330 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74330

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: 2
  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).