[CVE-2026-72318][IMPORTANT] cifs: validate DFS referral string offsets [ Upstream

[CVE-2026-72318][IMPORTANT] cifs: validate DFS referral string offsets [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72318
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: cifs: validate DFS referral string offsets [ Upstream
Commit: 76c607b9353d377b1d1b11db50e743eee0ccf658
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=76c607b9353d377b1d1b11db50e743eee0ccf658
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72318
Analysis date: Sat, 15 Aug 2026 06:11:01 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-72318 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72318

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-72318	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-125;*CWE-20;CWE-195;Other CVSS 'AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:H';BEST CVSS score: '8.6';DESCR 'SMB/CIFS DFS referral parsing can compute DfsPath and NetworkAddress pointers from server supplied offsets without first proving that the offsets stay inside the response buffer. A malicious or compromised SMB/DFS server can return a malformed referral that makes the computed string pointer exceed the received buffer, after which a negative max_len may be converted to a large size_t and used by kstrndup through the non Unicode path. This creates an out-of-bounds read in kernel memory and can cause a client kernel crash or limited information exposure depending on whether the overread data becomes observable through later path or referral processing. For the CVSS the PR:N is used because the attacking server does not need privileges on the victim system beyond being reachable by the CIFS client. The base score uses UI:R because a client normally has to mount or access the malicious DFS namespace, while the paranoid score uses UI:N for already configured or automatically accessed DFS deployments. Impact is at least denial of service and may include limited confidentiality or integrity impact, so this should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	OOB DISK INIT SIMPLEFIX SERVERTOCLIENT KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=5

1. ActionableScore
* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

2. Signal breakdown
* Remote reachable / network-triggerable: +2. A malicious or compromised SMB/DFS server can return malformed DFS referral offsets to a CIFS client.
* Reliable kernel crash / strong DoS: +1. The invalid offset can produce a negative max_len that becomes a large size_t and drives strnlen() out of bounds.
* Confidentiality impact plausible: +1. The primitive is an OOB read in kernel memory, and copied referral strings may make limited overread data observable through later processing.
* Broad/common subsystem exposure: +1. SMB/CIFS client mounts are common enough that this should not be treated as obscure, although DFS referral handling is configuration dependent.
* Paranoid Integrity impact plausible: +1. A corrupted referral path or network address string could affect subsequent DFS resolution behavior, but this is weaker than a direct write primitive.
* Paranoid Availability impact realistic: +1. If an affected client automatically follows DFS referrals, a malformed server response may repeatedly trigger a host-wide crash condition.

3. Reachability analysis
The attacker is typically a malicious SMB/DFS server, compromised server, or network attacker able to influence DFS referral responses. The victim does not need local privileges, but the CIFS client must mount or access a DFS namespace or otherwise process the referral. Existing configured mounts or automated access can reduce UI requirements. Containers and namespaces do not materially reduce the attacker side requirement, because the malformed input is supplied over the network to the kernel CIFS client. The path is not a generic packet receive path, but it is a realistic network filesystem client path.

4. Severity interpretation
This is more than an ordinary Moderate because it is network influenced and contains a concrete OOB read primitive in kernel memory. Realistic demonstrated impact is kernel crash / DoS, with plausible limited information exposure. There is no supported arbitrary write, UAF reclaim, type confusion, or strong LPE primitive, so it should not be treated as confirmed privilege escalation.

5. One-sentence report phrase
A malicious SMB/DFS server can provide out-of-buffer DFS referral string offsets to the CIFS client, causing an OOB kernel read and potential client kernel crash or limited information exposure.

6. Manual review recommendation
MANUAL CHECK REQUIRED. Network-influenced kernel OOB reads with crash and possible disclosure impact should not be auto-closed, even though no direct LPE or write primitive is shown.

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

Patch: cifs: validate DFS referral string offsets [ Upstream
Commit: 76c607b9353d377b1d1b11db50e743eee0ccf658
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=76c607b9353d377b1d1b11db50e743eee0ccf658

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=76c607b9353d377b1d1b11db50e743eee0ccf658

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

The original Linux kernel CVE announcement for CVE-2026-72318 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72318

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:L/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: 5
  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).