[CVE-2026-46214][MODERATE 7.0] vsock/virtio: fix accept queue count leak on transport mismatch

[CVE-2026-46214][MODERATE 7.0] vsock/virtio: fix accept queue count leak on transport mismatch

[AL-KERNEL]

CVE: CVE-2026-46214
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: vsock/virtio: fix accept queue count leak on transport mismatch
Commit: 65c484726e74013a2ec7ba67a34d87760ae8f390
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=65c484726e74013a2ec7ba67a34d87760ae8f390
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46214
Analysis date: Thu, 28 May 2026 09:08:46 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
A virtio-vsock peer can repeatedly trigger transport mismatch failures that leak accept queue accounting, eventually making the listener reject all new connections and causing a host/guest service DoS.

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

The original Linux kernel CVE announcement for CVE-2026-46214 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46214

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: 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
======================================================================

CVE-2026-46214	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-772;**CWE-400;*CWE-664;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'virtio vsock listener accounting could be corrupted because sk_acceptq_added was called before transport validation and was not undone when vsock_assign_transport failed or selected another transport. A peer with access to the virtio vsock channel can repeat failing connection attempts until sk_ack_backlog appears full, after which the listener rejects new connections. For the CVSS the PR:N is used because the paranoid scenario only requires the ability to send vsock connection attempts from the peer side, not local privileges on the victim. The issue is not Internet reachable but can cross a host guest virtualization boundary where virtio vsock is exposed. Impact is denial of service for the affected listener only, with no supported memory corruption, information disclosure, or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) 	MAYBE	VIRT WARNONLY SIMPLEFIX LEAK ERRORPATH  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	-	-	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

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

## 2. Signal breakdown

Conservative signals:

* Adjacent / virtualization-channel reachable: +2. A peer on the virtio-vsock channel can send connection attempts to the affected listener.
* Reliable listener DoS: +1. Repeated transport mismatch failures can permanently increase `sk_ack_backlog` until the listener rejects new connections.
* Availability impact realistic: +1. The affected vsock service can become unavailable to new clients.

Paranoid additional signal:

* Cross-boundary isolation impact: +1. The issue can matter across a host/guest boundary when virtio-vsock is used for host-guest services or agent communication.

Limiting factors:

* No memory corruption.
* No UAF, double free, OOB write, information leak, or privilege escalation primitive.
* Not Internet reachable.
* Trigger depends on multi-transport mismatch or failure conditions, not ordinary successful connects.

## 3. Reachability analysis

The bug can be triggered by a peer that can send virtio-vsock connection attempts to a listening socket. This may be a guest-to-host, host-to-guest, or guest service scenario depending on deployment.

No local privileges on the victim are needed for the paranoid peer-triggered scenario, but the attacker must have access to the relevant vsock communication boundary. Containers matter only if vsock access is delegated into the container.

The path is not exposed to normal TCP/IP networks. It is relevant mainly for VM environments using virtio-vsock services.

## 4. Severity interpretation

This behaves like an actionable Moderate issue. The realistic impact is denial of service for a specific vsock listener by exhausting its logical accept backlog through accounting leakage.

It does not behave like an Important memory-corruption vulnerability. The patch supports availability impact only, with no confidentiality, integrity, or LPE evidence.

## 5. One-sentence report phrase

A virtio-vsock peer can repeatedly trigger transport mismatch failures that leak accept queue accounting, eventually making the listener reject all new connections and causing a host/guest service DoS.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Review is recommended for environments exposing important virtio-vsock services across host/guest boundaries, but the issue should remain availability-only unless additional evidence shows memory corruption or privilege escalation.

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

Patch: vsock/virtio: fix accept queue count leak on transport mismatch
Commit: 65c484726e74013a2ec7ba67a34d87760ae8f390
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=65c484726e74013a2ec7ba67a34d87760ae8f390

Commit description:

virtio_transport_recv_listen() calls sk_acceptq_added() before
vsock_assign_transport(). If vsock_assign_transport() fails or
selects a different transport, the error path returns without
calling sk_acceptq_removed(), permanently incrementing
sk_ack_backlog.

After approximately backlog+1 such failures, sk_acceptq_is_full()
returns true, causing the listener to reject all new connections.

Fix by moving sk_acceptq_added() to after the transport validation,
matching the pattern used by vmci_transport and hyperv_transport.

Fixes: c0cfa2d ("vsock: add multi-transports support")
Signed-off-by: Dudu Lu <phx0fer@gmail.com>
Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>
Reviewed-by: Luigi Leonardi <leonardi@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://patch.msgid.link/20260413131409.19022-1-phx0fer@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Cc: Luigi Leonardi <leonardi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/vmw_vsock/virtio_transport_common.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=65c484726e74013a2ec7ba67a34d87760ae8f390

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

The original Linux kernel CVE announcement for CVE-2026-46214 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46214

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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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).