[CVE-2026-74359][IMPORTANT] configfs_lookup(): don't leave ->s_dentry dangling on failure [ Upstream

[CVE-2026-74359][IMPORTANT] configfs_lookup(): don't leave ->s_dentry dangling on failure [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74359
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: configfs_lookup(): don't leave ->s_dentry dangling on failure [ Upstream
Commit: 3e83b2203aa59bd279e4f677ec793d49dc9d019e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3e83b2203aa59bd279e4f677ec793d49dc9d019e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74359
Analysis date: Sat, 15 Aug 2026 17:24:50 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A failed inode allocation in `configfs_lookup()` can leave `sd->s_dentry` pointing to a soon-freed dentry, allowing a later `getdents(2)` call to dereference stale kernel memory and potentially cause a local crash or worse UAF impact.

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

The original Linux kernel CVE announcement for CVE-2026-74359 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74359

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: IMPORTANT
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-2026-74359	IMPORTANT	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-416;CWE-825;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'configfs_lookup can leave sd s_dentry pointing to a dentry that never became positive when configfs_create fails during inode allocation. A later getdents call in the same directory can dereference this stale pointer while reading the inode number, creating a kernel use after free condition. For the CVSS the PR:L is used for the paranoid score because a local user or local process with access to a mounted configfs hierarchy may be able to trigger lookup and directory enumeration, while reliable triggering also depends on allocation failure or memory pressure. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality and integrity impact due to the UAF primitive, so privilege escalation cannot be ruled out without manual review.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)	YES	LOCK DANGER DISK UAF LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local process that can access the mounted configfs hierarchy can trigger lookup and later getdents.
* Memory corruption, strong corruption primitive: +2. The commit explicitly describes a dangling `s_dentry` pointer and subsequent use-after-free.
* Real lifetime corruption: +1. This is a stale pointer after failed inode allocation and later dentry free.
* Reliable kernel crash / strong DoS: +1. Subsequent `getdents(2)` may dereference the freed dentry.
* Hard or unreliable condition: -1. Reliable triggering depends on inode allocation failure or memory pressure.
* Configuration/exposure limitation: -1. configfs must be enabled, mounted, and reachable to the attacker.

Paranoid additions:

* Weak LPE concern: +1. The stale dentry pointer is a real kernel UAF, and local filesystem object churn may allow reuse concerns, although no controlled reclaim is shown.
* Confidentiality impact plausible: +1. UAF reuse could theoretically expose kernel object state.
* Integrity impact plausible: +1. UAF reuse could theoretically affect integrity, but no write primitive is demonstrated.

## 3. Reachability analysis

The bug is local only and is not network reachable. Triggering requires access to a configfs directory and an inode allocation failure during `configfs_lookup()`, followed by directory enumeration through `getdents(2)`. In typical deployments, configfs is mounted by root and many write/configuration operations require privileges, but read and lookup permissions may be available depending on the mounted hierarchy and subsystem permissions. Namespaces or containers could matter if configfs is exposed inside a container or to a reduced-privilege service account, but this is not a default remote attack surface.

Call-site confidence: high. The commit directly identifies the failure path in `configfs_lookup()` and the later dereference path via `getdents(2)`.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup because the patch fixes an explicit kernel use-after-free. Realistic exploitation is constrained by the need to hit inode allocation failure, so the conservative score stays borderline. The paranoid score is higher because kernel UAF bugs can sometimes become more than DoS after object reuse, but the patch does not show arbitrary write, callback control, type confusion, or a demonstrated privilege escalation primitive. This should be treated as Actionable Moderate at minimum and a Strong Important candidate for manual review.

## 5. One-sentence report phrase

A failed inode allocation in `configfs_lookup()` can leave `sd->s_dentry` pointing to a soon-freed dentry, allowing a later `getdents(2)` call to dereference stale kernel memory and potentially cause a local crash or worse UAF impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: explicit kernel UAF with local reachability and possible object reuse concerns, even though reliable exploitation beyond DoS is not demonstrated and depends on allocation-failure timing.

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

Patch: configfs_lookup(): don't leave ->s_dentry dangling on failure [ Upstream
Commit: 3e83b2203aa59bd279e4f677ec793d49dc9d019e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3e83b2203aa59bd279e4f677ec793d49dc9d019e

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=3e83b2203aa59bd279e4f677ec793d49dc9d019e

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

The original Linux kernel CVE announcement for CVE-2026-74359 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74359

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: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: 4
  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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).