[CVE-2026-46234][MODERATE REGULAR] vsock: fix buffer size clamping order

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

CVE: CVE-2026-46234
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: vsock: fix buffer size clamping order
Commit: a998a7e250bf976539e05a00ec64a81292afecaa
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a998a7e250bf976539e05a00ec64a81292afecaa
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46234
Analysis date: Thu, 28 May 2026 07:09:08 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / Ordinary Moderate at minimum
Manual review required: NO

Summary:
A wrong clamp order in `vsock_update_buffer_size()` lets a local VSOCK user make `buffer_size` exceed `buffer_max_size`, potentially causing resource exhaustion but not memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-46234 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46234

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: NO

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-2026-46234	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';**CWE-400;CWE-770;CWE-682;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'vsock_update_buffer_size() applied the maximum clamp before the minimum clamp, so a local process could configure the minimum buffer size larger than the maximum and make vsk buffer_size exceed vsk buffer_max_size. This breaks the intended socket memory boundary and can allow higher than expected vsock buffering or credit limits. For the CVSS the PR:L is used because triggering requires a local user or process able to create vsock sockets and set the related socket options, not administrator privileges. The issue is not directly network reachable because a remote vsock peer cannot normally set these local socket options. Impact is denial of service or resource exhaustion only, with no supported evidence of information disclosure, memory corruption, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Borderline / Ordinary Moderate at minimum (with actual score 3)	YES	SIMPLEFIX IMPROVEONLY LINUS  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline / Ordinary Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local process able to create AF_VSOCK sockets and set related socket options can reach the affected path.

* Availability impact realistic: +1
  The broken clamp order can allow `vsk->buffer_size` to exceed `vsk->buffer_max_size`, weakening intended socket memory limits and enabling possible resource exhaustion.

Paranoid additional signal:

* Broad or common virtualization exposure: +1
  VSOCK is common in VM guest or host communication environments, especially cloud and virtualization stacks, although it is not a universal default interface.

Non-applied signals:

* No memory corruption signal.
  The patch fixes a bounds or policy logic error, not UAF, OOB write, type confusion, or arbitrary write.

* No privilege escalation signal.
  There is no demonstrated primitive for LPE.

* No remote network signal.
  A remote VSOCK peer normally cannot set the local socket options needed to trigger the bad clamp order.

## 3. Reachability analysis

The bug is triggered locally by a process that can use VSOCK sockets and configure buffer size socket options. It does not require root in principle, but availability depends on whether AF_VSOCK is enabled and exposed in the environment. Containers may matter if VSOCK access is passed through or permitted by policy. Realistic exploitation is limited to resource exhaustion or bypass of intended socket memory boundaries, not code execution.

## 4. Severity interpretation

This behaves like an ordinary Moderate resource limit bug, with a borderline score only in VSOCK-heavy multi-tenant virtualization environments. The theoretical impact is excessive buffering or memory pressure. The realistic evidence does not support memory corruption, confidentiality impact, integrity impact, or privilege escalation.

## 5. One-sentence report phrase

A wrong clamp order in `vsock_update_buffer_size()` lets a local VSOCK user make `buffer_size` exceed `buffer_max_size`, potentially causing resource exhaustion but not memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a local resource-boundary logic bug without a memory corruption primitive. Manual review is only useful for multi-tenant virtualization deployments where untrusted users have VSOCK access.

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

Patch: vsock: fix buffer size clamping order
Commit: a998a7e250bf976539e05a00ec64a81292afecaa
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a998a7e250bf976539e05a00ec64a81292afecaa

Commit description:

In vsock_update_buffer_size(), the buffer size was being clamped to the
maximum first, and then to the minimum. If a user sets a minimum buffer
size larger than the maximum, the minimum check overrides the maximum
check, inverting the constraint.

This breaks the intended socket memory boundaries by allowing the
vsk->buffer_size to grow beyond the configured vsk->buffer_max_size.

Fix this by checking the minimum first, and then the maximum. This
ensures the buffer size never exceeds the buffer_max_size.

Fixes: b9f2b0f ("vsock: handle buffer_size sockopts in the core")
Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Norbert Szetei <norbert@doyensec.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://patch.msgid.link/180118C5-8BCF-4A63-A305-4EE53A34AB9C@doyensec.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Cc: Luigi Leonardi <leonardi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/vmw_vsock/af_vsock.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=a998a7e250bf976539e05a00ec64a81292afecaa

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

The original Linux kernel CVE announcement for CVE-2026-46234 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46234

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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 3

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).