[CVE-2026-68343][MODERATE 7.0] smb: client: validate DFS referral PathConsumed [ Upstream

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

CVE: CVE-2026-68343
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: smb: client: validate DFS referral PathConsumed [ Upstream
Commit: 5b439f39f33ec15d319ced3b025e122346fba987
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5b439f39f33ec15d319ced3b025e122346fba987
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68343
Analysis date: Mon, 10 Aug 2026 18:18:07 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malformed SMB DFS referral can provide a PathConsumed value larger than the client search name, causing later DFS path parsing to advance beyond the path buffer and potentially crash the kernel SMB client.

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

The original Linux kernel CVE announcement for CVE-2026-68343 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68343

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
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CVE-2026-68343	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H';*CWE-20;CWE-125;CWE-126;Other CVSS 'AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H';BEST CVSS score: '8.6';DESCR 'A malformed DFS referral response can set PathConsumed larger than the SMB client search name. Later DFS path parsing may then advance beyond the end of the path string, creating an out-of-bounds read risk and a likely kernel crash on the client side. For the CVSS the PR:N is used because a malicious or compromised SMB DFS server can send the malformed referral without needing privileges on the victim host. The base score uses UI:R because the victim normally has to connect to or use the affected SMB DFS path. The paranoid score uses UI:N for already configured enterprise DFS environments where the client may contact the attacker controlled server automatically. Impact is at least denial of service and may include limited confidentiality or integrity impact from out-of-bounds path parsing, but there is no clear arbitrary write primitive in this patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	DISK INIT SERVERTOCLIENT KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

* Remote reachable / network-triggerable: +2
  A malicious or compromised SMB/DFS server can return a malformed DFS referral response to the SMB client.

* Reliable kernel crash / strong DoS: +1
  The unchecked PathConsumed value can make later DFS path parsing advance beyond the end of the search name. The most concrete impact is client-side kernel fault or crash.

* Important filesystem/storage path: +1
  This is in the SMB client filesystem path and affects DFS referral parsing during path resolution.

* Broad/common subsystem or broadly deployed exposure: +1, paranoid only
  SMB/CIFS clients are common in enterprise environments, and DFS referrals may be used automatically once mounts or domain paths are configured. This raises practical triage priority, but exposure still depends on SMB client use.

Not counted:

* Generic strong memory corruption: +0
  The patch supports an out-of-bounds path parsing or OOB read concern, but does not show OOB write, UAF, double free, arbitrary write, type confusion, or attacker-controlled reclaim.

* Privilege escalation plausible: +0
  No concrete LPE primitive is shown.

* Confidentiality / Integrity impact: +0 conservative
  There is no demonstrated read-back disclosure path or write primitive. Paranoid CVSS may keep C:L/I:L for manual review sensitivity, but ActionableScore should not strongly count it without a clearer primitive.

## 3. Reachability analysis

The attacker is a malicious or compromised SMB/DFS server, or an actor able to influence DFS referral responses. No privileges are needed on the victim host in CVSS terms, but the victim client normally needs to connect to or already use the affected SMB/DFS path.

This is not a packet-processing bug against any random host. It is a client-side network parser issue. In managed enterprise environments, DFS paths may be configured or contacted automatically, so UI may be lower in practice than in a simple manual-mount scenario.

Namespaces and containers are not the main factor here. The relevant exposure is whether the host kernel SMB client is used and whether untrusted SMB/DFS servers can be reached.

## 4. Severity interpretation

This is stronger than an ordinary low-risk Moderate because it is a remote parser issue in a filesystem client and can plausibly cause kernel-side OOB path parsing and DoS. It does not reach a strong Important classification on the provided evidence because the patch does not show a write primitive, UAF, object lifetime corruption, type confusion, or a demonstrated information leak.

The realistic impact is remote client-side DoS through a malicious SMB/DFS response. The theoretical concern is limited C/I impact from out-of-bounds path parsing, but this remains a manual-review reason rather than proven Important-class exploitation.

## 5. One-sentence report phrase

A malformed SMB DFS referral can provide a PathConsumed value larger than the client search name, causing later DFS path parsing to advance beyond the path buffer and potentially crash the kernel SMB client.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: network-reachable client-side parser issue, malformed remote filesystem response, and OOB path parsing risk. The evidence supports Actionable Moderate handling even though a concrete privilege-escalation or arbitrary-write primitive is not shown.

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

Patch: smb: client: validate DFS referral PathConsumed [ Upstream
Commit: 5b439f39f33ec15d319ced3b025e122346fba987
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5b439f39f33ec15d319ced3b025e122346fba987

Changed files:
  fs/smb/client/misc.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=5b439f39f33ec15d319ced3b025e122346fba987

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

The original Linux kernel CVE announcement for CVE-2026-68343 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68343

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:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 8.6

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: 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: YES
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).