[CVE-2026-93829][LOW] smb: client: fix races in cifsd thread creation [ Upstream

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

CVE: CVE-2026-93829
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: smb: client: fix races in cifsd thread creation [ Upstream
Commit: ee8f811cbac56ffb738b3a73671a9e75b0f56e99
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee8f811cbac56ffb738b3a73671a9e75b0f56e99
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93829
Analysis date: Thu, 24 Sep 2026 13:53:11 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-93829 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93829

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-2026-93829	LOW	https://www.kernelcve.org/list/?q=CVE-2026-93829 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:N/I:N/A:H';CWE-362;CWE-667;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A race in SMB client session creation allows the cifsd demultiplex thread to run before the tcp_ses structure is fully initialized and before its tsk pointer is reliably published. The thread can access partially initialized state without locking and can enter an incorrect exit or wait state if it runs before tcp_ses tsk is assigned. This can cause CIFS SMB connection setup failures or stalled client session handling. For the CVSS the PR:L is used because a service account container root or user with delegated CIFS mount or SMB client session capability may be sufficient to trigger the affected local path. The race requires a narrow scheduling window so AC:H is appropriate. A remote SMB server can participate in a connection scenario but does not by itself reliably control the local thread scheduling race. Impact is primarily local denial of service. No concrete use after free out of bounds access arbitrary write or information disclosure primitive is shown by the patch.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	LOCK DISK RACE SERVERTOCLIENT  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::

The conservative and paranoid scores are identical because the supplied patch establishes an initialization and scheduling race, but does not establish a post-free access, memory corruption, controlled state reuse, information disclosure, authorization bypass, or a stronger attacker-controlled primitive.

2. Signal breakdown

* +1 Availability impact realistic. The cifsd thread can observe a partially initialized tcp_ses structure or an unpublished tcp_ses tsk pointer. The supplied commit explicitly describes a possible wait for SIGKILL and stalled SMB client session handling.
* +0 Real UAF. No object is shown to be freed while another path retains and dereferences it.
* +0 Kernel memory corruption. No OOB access, arbitrary write, stale freed object, refcount mutation, type confusion, or controlled replacement is established.
* +0 Remote reachability. An SMB server may be involved in connection setup, but the bug depends on a local thread creation and scheduling order. The server is not shown to control that order.
* +0 Local unprivileged trigger. The supplied evidence does not establish that an ordinary unprivileged user can complete CIFS session creation or mounting on the evaluated system.
* +0 Reduced privilege penalty. A below-host-admin delegated mount capability is mentioned in prior analysis, but is not established by the supplied patch and context.
* +0 Host-admin penalty. Host-admin-equivalent privilege is not positively established.
* +0 Namespace-scoped reachability. No complete namespace-scoped trigger chain is established.
* +0 Hard race penalty. The issue is a race, but the supplied evidence does not establish a materially rare, externally uncontrollable, or one-shot timing condition sufficient for a negative point.
* +0 Reliable kernel crash. The patch describes an incorrect thread wait or session stall, not a demonstrated kernel panic, Oops, or host-wide crash.
* +0 Confidentiality and integrity impact. No disclosure path or unauthorized modification primitive is shown.
* +0 Strong or weak LPE leverage. The partially initialized fields are not shown to provide attacker-controlled post-initialization object reuse, callback control, pointer corruption, or a security-sensitive state transition.

Important non-awarded signals:

* Controlled reclaim is not demonstrated.
* Arbitrary or directed kernel write is not demonstrated.
* A concrete second release, put, free, or refcount mutation on a dangling object is not present.
* Structured stale-object leverage is not applicable because tcp_ses is not shown to be freed or reused.
* Extra Availability impact is not awarded because there is no independently demonstrated host-wide crash, persistent filesystem failure, or cross-container exhaustion effect.

3. Reachability analysis

The vulnerable operation occurs in cifs_get_tcp_session while the Linux SMB client creates a tcp_ses object and starts the cifsd demultiplex thread. The immediate trigger requires local creation of an SMB client session, typically through a CIFS mount or another client session setup path.

The supplied patch does not establish whether the complete session creation path is reachable by an ordinary user, a namespace-scoped capability, a delegated mount service, or only a host administrator in the evaluated deployment. Therefore HostAdminRequired is UNKNOWN and NamespaceScopedPrivilege is UNKNOWN.

A remote SMB server can participate in the connection attempt, but the defect occurs because the local cifsd thread may execute between kthread_run and later tcp_ses field initialization. The supplied evidence does not show that a remote server can reliably cause or control the required local scheduling interleaving. This is not directly network-triggerable for triage purposes.

No special hardware, boot option, sysctl, device assignment, or prior host-side topology is identified. The race can occur during normal SMB client session creation, but no attacker-controlled repeated lifetime manipulation or security-relevant data-plane control is established.

4. Primitive and severity interpretation

The exact primitive is an initialization-order race. The cifsd kernel thread may run before tcp_ses fields are fully populated and before tcp_ses tsk has been assigned. The demonstrated consequence is incorrect thread behavior, including possible waiting for SIGKILL and stalled CIFS SMB session handling.

This is not a UAF. The supplied patch does not show tcp_ses being freed, released, replaced, or accessed after its lifetime ends. It also does not show a second lifetime or refcount mutation, an active stale-object reuse condition, controlled replacement, an attacker-controlled post-free payload, an OOB access, or a write primitive.

The affected object is an active structured session object, but object complexity alone does not establish exploitation leverage. The visible stale behavior is limited to observing fields before initialization, not using freed or reclaimed storage. The bug is therefore CLASS_C rather than CLASS_B.

ImportantCandidate is NO because the patch supports a local availability and correctness issue only. AutoDowngradeAllowed is YES because no unresolved concrete lifetime-corruption, authorization, ownership, or boundary-bypass primitive would be discarded by an ordinary Moderate classification. Operationally, this is a low-priority client-session reliability issue, potentially causing failed or stalled CIFS SMB connection establishment.

5. One-sentence report phrase

A race during SMB client session creation can start the cifsd thread before tcp_ses initialization is complete, causing stalled CIFS SMB session handling but no demonstrated memory corruption or privilege escalation.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The supplied patch establishes an initialization race and local availability impact, but does not establish a UAF, memory corruption primitive, remote trigger, security-boundary bypass, or meaningful unresolved exploitation leverage.

7. Call-site confidence

Call-site confidence: medium

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

Patch: smb: client: fix races in cifsd thread creation [ Upstream
Commit: ee8f811cbac56ffb738b3a73671a9e75b0f56e99
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee8f811cbac56ffb738b3a73671a9e75b0f56e99

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=ee8f811cbac56ffb738b3a73671a9e75b0f56e99

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

The original Linux kernel CVE announcement for CVE-2026-93829 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93829

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:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: unknown
  Paranoid ActionableScore: 1

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).