[CVE-2026-74259][MODERATE 7.0] cifs: remove all cifs files before kill super [ Upstream

[CVE-2026-74259][MODERATE 7.0] cifs: remove all cifs files before kill super [ Upstream

[AL-KERNEL]

CVE: CVE-2026-74259
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: cifs: remove all cifs files before kill super [ Upstream
Commit: 55fb9581986141659002264fdc75cef307811eb8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=55fb9581986141659002264fdc75cef307811eb8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74259
Analysis date: Sat, 15 Aug 2026 21:59:11 -0400
ActionableScore: 5
ActionableScore lower bound: 2
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A CIFS unmount lifetime race can allow delayed fileinfo cleanup work to run after superblock teardown, causing a NULL pointer dereference in the dput/list_lru path and a local kernel crash, with practical triggering usually requiring delegated or administrative mount and network-control privileges.

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

The original Linux kernel CVE announcement for CVE-2026-74259 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74259

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-2026-74259	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:L/UI:N/S:U/C:L/I:L/A:H';CWE-362;*CWE-416;**CWE-476;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A CIFS lifetime race can occur during umount when cifsFileInfo objects are queued to fileinfo_put_wq and the asynchronous final put runs after CIFS superblock teardown has already progressed. The observed failure is a NULL pointer dereference in the dput and list_lru_add path, causing a kernel crash and local denial of service. The bug is not directly network reachable because the trigger is the local mount and umount control path, although the reproducer depends on a CIFS network mount and a network disruption. For the CVSS the PR:L is used for the paranoid score because practical triggering may be possible for a reduced capability root, container root, or service account that can mount and unmount CIFS and affect the network path. Impact is at least local denial of service and in worst case may allow limited confidentiality or integrity impact due to lifetime race and UAF style behavior, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)  SKIP CVE-2026-74259 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 340cea84f691c5206561bb2e0147158fe02070be YES  NO NO unknown 	MAYBE	DANGER NULLPTR DISK INIT SERVERTOCLIENT  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=5
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: **2**
* Paranoid score: **5**
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Memory corruption, weak or indirect corruption candidate: +1**
  The observed failure is a NULL dereference, but the root cause is delayed `cifsFileInfo` finalization after CIFS superblock teardown. This is a lifetime bug, but no controlled reclaim, overwrite, callback control, or type confusion is shown.

* **Real lifetime corruption: +1**
  `fileinfo_put_wq` can run after `umount` teardown has progressed. The fix flushes `serverclose_wq` and `fileinfo_put_wq` before freeing superblock related state.

* **Reliable kernel crash / strong DoS: +1**
  The commit includes a concrete BUG trace in `list_lru_add -> d_lru_add -> dput -> cifsFileInfo_put_final`.

* **Important filesystem/storage path: +1**
  CIFS is a filesystem client path involving open file lifetime and unmount cleanup.

* **Requires admin/root/CAP_SYS_ADMIN/CAP_NET_ADMIN in typical deployments: -2**
  Reliable triggering normally requires CIFS mount and network namespace or firewall manipulation, which are privileged operations in typical host deployments.

Paranoid adjustment:

* The paranoid score does **not** apply the full privilege penalty because reduced-capability root, container root, or a storage management service may have delegated mount or network-control permissions without being equivalent to full host root.
* No strong LPE bonus is awarded because the patch does not show attacker-controlled reclaim, write-after-free, object replacement, callback dispatch, or arbitrary write.
* The issue is therefore actionable due to lifetime corruption plus reliable crash in a filesystem client path, but it is not a Strong Important candidate from the supplied evidence.

Call-site confidence: **high**. The relevant teardown site and the workqueue flush fix are visible in the patch, and the crash stack reaches `cifsFileInfo_put_final`.

## 3. Reachability analysis

The trigger is local and control-plane oriented. An attacker needs the ability to mount and unmount CIFS and to create the network disruption or teardown timing that leaves fileinfo cleanup queued past superblock teardown. In normal deployments this implies administrative privileges such as `CAP_SYS_ADMIN` and possibly `CAP_NET_ADMIN`.

Namespaces and containers matter. If a container root or service account is delegated CIFS mount capability or network control without full host-root trust, the practical privilege level is lower than classic PR:H, and a host kernel crash becomes a cross-boundary availability concern.

The issue is not directly network reachable. The CIFS server or network path can influence timing and failure behavior, but the vulnerability is primarily triggered through local mount and umount lifecycle control.

## 4. Severity interpretation

This behaves more like an **Actionable Moderate** than an ordinary Low or auto-close Moderate. The demonstrated impact is a reliable local kernel crash. Theoretical memory-corruption concern exists because delayed work can outlive teardown state, but the patch and trace mainly support NULL dereference / lifetime race DoS rather than a proven privilege escalation primitive.

It should not be upgraded to Important solely from the supplied evidence. There is no demonstrated attacker-controlled UAF reclaim, arbitrary write, type confusion, stale callback, or credential/security-boundary bypass. The paranoid score is still elevated to avoid missing a lifetime bug in filesystem cleanup that may need human review.

## 5. One-sentence report phrase

A CIFS unmount lifetime race can allow delayed fileinfo cleanup work to run after superblock teardown, causing a NULL pointer dereference in the dput/list_lru path and a local kernel crash, with practical triggering usually requiring delegated or administrative mount and network-control privileges.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is a race/lifetime bug in filesystem teardown with a demonstrated kernel crash and UAF-style timing. Even though the current evidence mainly supports DoS, the async cleanup after superblock teardown is worth manual review before auto-closing.

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

Patch: cifs: remove all cifs files before kill super [ Upstream
Commit: 55fb9581986141659002264fdc75cef307811eb8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=55fb9581986141659002264fdc75cef307811eb8

Changed files:
  fs/smb/client/connect.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=55fb9581986141659002264fdc75cef307811eb8

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

The original Linux kernel CVE announcement for CVE-2026-74259 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74259

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:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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).