[CVE-2026-64598][MODERATE REGULAR] smb/client: Fix error code in smb2_aead_req_alloc()

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

CVE: CVE-2026-64598
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: smb/client: Fix error code in smb2_aead_req_alloc()
Commit: aa37f5fef78dd11cbf983269da2031e12625c56d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aa37f5fef78dd11cbf983269da2031e12625c56d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64598
Analysis date: Thu, 06 Aug 2026 04:15:53 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
An error-code signedness bug in `smb2_aead_req_alloc()` can return a malformed error pointer after `cifs_get_num_sgs()` fails, and a later dereference may crash the kernel in SMB client AEAD I/O handling.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64598 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64598

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 REGULAR
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-2026-64598	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';CWE-681;CWE-704;**CWE-476;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.9';DESCR 'SMB client AEAD request allocation can return a malformed error pointer because a negative cifs_get_num_sgs result is stored in an unsigned num_sgs value before ERR_PTR is built. If the caller treats that malformed pointer as a valid allocation result, a later dereference can crash the kernel. For the CVSS the PR:N is used for the paranoid score because a malicious or compromised SMB server may not need an account on the client once the victim client already connects to or mounts the share. The issue is potentially network reachable in SMB client deployments, but reliable triggering likely requires specific error conditions in scatterlist calculation or request construction. Impact is denial of service via kernel crash. No reliable confidentiality or integrity primitive is evident from this signedness and invalid pointer handling bug.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)	YES	DANGER DISK SIMPLEFIX SERVERTOCLIENT  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**

## 2. Signal breakdown

Paranoid score signals:

* Remote reachable / network-triggerable: +2
  SMB client code can be influenced by a malicious or compromised SMB server after the victim client connects or mounts the share.
* Reliable kernel crash / strong DoS: +1
  The commit explicitly says the malformed error pointer can eventually be dereferenced and crash the kernel.
* Important filesystem/storage path: +1
  This is in the SMB/CIFS filesystem client I/O crypto path.
* Hard or unreliable trigger: -1
  Triggering likely requires specific failure conditions in `cifs_get_num_sgs()` and AEAD request construction, not just any SMB packet.
* Broad/common subsystem exposure: +1
  SMB/CIFS client support is common in enterprise and desktop environments, though not always mounted by default.

Conservative score signals:

* Local user or local workload trigger after mount: +1
  A local process may trigger SMB client I/O if an SMB share is already mounted.
* Reliable kernel crash / strong DoS: +1
  Invalid error pointer dereference can crash the kernel.
* Hard or unreliable trigger: -1
  Specific error-path conditions are needed.
* Important filesystem/storage path: +1
  SMB client filesystem I/O path.

No memory-corruption or LPE bonus is added. This is best classified as invalid error-pointer handling leading to NULL or invalid pointer dereference, not UAF, OOB write, double free, type confusion, or arbitrary write.

## 3. Reachability analysis

The conservative trigger model is local: a user or process causes SMB client I/O on an already mounted share. Mounting SMB shares is usually privileged, but using an already mounted share may be available to unprivileged users depending on system policy.

The paranoid trigger model is network-assisted: a malicious or compromised SMB server may influence the client-side path once the victim has connected to that server. This is not a remotely exposed server-side service on the victim, so it is weaker than a classic AV:N listening-daemon bug. However, SMB client vulnerabilities are still actionable because enterprise clients often connect to remote shares.

Namespaces and containers do not clearly lower requirements unless the container can access a host SMB mount or initiate CIFS mounts through delegated privileges. The path is not guaranteed default-active because it requires SMB client use and likely encrypted or AEAD-related request handling.

Call-site confidence: medium. The patch shows the faulty return value construction, but not all callers and dereference sites.

## 4. Severity interpretation

This behaves like an actionable Moderate / borderline manual-review issue, not an Important-class vulnerability based on the supplied patch alone.

Theoretical risk is limited to an invalid pointer dereference and kernel crash. There is no evidence of attacker-controlled reclaim, stale object reuse, write-after-free, type confusion, arbitrary write, or information disclosure. Therefore C and I remain unsupported, while A impact is realistic.

The reason not to auto-close immediately is the SMB client network-filesystem context: a malicious server may be able to participate in triggering the client crash, but practical reliability and exact preconditions need validation.

## 5. One-sentence report phrase

An error-code signedness bug in `smb2_aead_req_alloc()` can return a malformed error pointer after `cifs_get_num_sgs()` fails, and a later dereference may crash the kernel in SMB client AEAD I/O handling.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: network-assisted SMB client DoS is plausible, but the patch supports crash impact only and does not show a concrete confidentiality, integrity, or privilege-escalation primitive.

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

Patch: smb/client: Fix error code in smb2_aead_req_alloc()
Commit: aa37f5fef78dd11cbf983269da2031e12625c56d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=aa37f5fef78dd11cbf983269da2031e12625c56d

Commit description:

The "*num_sgs" variable is a u32 so "ERR_PTR(*num_sgs)" doesn't work.
We would have to do something similar to the previous line where it's
cast to int and then long.  However, it's simpler to store the return in
an int ret variable.

This bug would eventually result in a crash when dereference the invalid
error pointer.

Fixes: d08089f ("cifs: Change the I/O paths to use an iterator rather than a page list")
Cc: stable@kernel.org
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/smb/client/smb2ops.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=aa37f5fef78dd11cbf983269da2031e12625c56d

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

The original Linux kernel CVE announcement for CVE-2026-64598 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64598

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:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.9

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: 4

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 REGULAR

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).