[CVE-2026-53132][MODERATE 7.0] vsock/virtio: fix potential unbounded skb queue

[CVE-2026-53132][MODERATE 7.0] vsock/virtio: fix potential unbounded skb queue

[AL-KERNEL]

CVE: CVE-2026-53132
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: vsock/virtio: fix potential unbounded skb queue
Commit: 1eca304f97a34ed5e921e1f0e06c8b241f25bf12
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1eca304f97a34ed5e921e1f0e06c8b241f25bf12
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53132
Analysis date: Thu, 25 Jun 2026 04:57:48 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
A virtio-vsock receive accounting bug allows a vsock peer to queue many zero-length EOM skb objects without increasing payload accounting, causing resource exhaustion and denial of service on the receiving endpoint.

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

The original Linux kernel CVE announcement for CVE-2026-53132 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53132

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.

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

CVE-2026-53132	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-770;**CWE-400;CWE-404;Other CVSS 'AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.7';DESCR 'virtio vsock receive accounting can be bypassed with zero length packets marked VIRTIO_VSOCK_SEQ_EOM because payload bytes stay at zero while each queued skb still consumes kernel memory. A peer on the vsock boundary can create a very large receive queue and cause resource exhaustion on the target endpoint. For the CVSS the PR:L is used because exploitation normally requires a local process in a guest or host endpoint that can open or use a vsock connection, but does not require administrator privileges on the target kernel. The issue is adjacent network reachable through the virtualization transport, not directly reachable from the public Internet. Impact is denial of service through memory pressure or kernel resource exhaustion. No confidentiality or integrity impact is assigned because the patch indicates unbounded queue growth rather than UAF, OOB access, or an arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	VIRT SIMPLEFIX SKB IMPROVEONLY LINUS PACKET  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	YES	NO	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:

* Local unprivileged trigger: +1
  A non-admin process on a guest or host endpoint that can use virtio-vsock may be able to send zero-length EOM packets.

* Reliable kernel crash / strong DoS: +1
  The bug allows an unbounded number of skb objects to accumulate because payload accounting stays at zero while metadata memory grows.

* Cross-boundary isolation / resource bypass: +1
  The issue crosses the virtio-vsock guest-host communication boundary and bypasses the intended per-socket receive buffer accounting.

* Availability impact realistic: +1
  Sustained abuse can create kernel memory pressure or resource exhaustion on the receiving endpoint.

Paranoid additional signal:

* Broad virtualization exposure: +1
  virtio-vsock is common in virtualized environments, container-adjacent setups, and guest-host service channels, even though it is not Internet-reachable.

No memory-corruption signals were counted. The patch shows accounting bypass and unbounded queue growth, not UAF, OOB write, object confusion, or arbitrary write.

## 3. Reachability analysis

The bug is triggerable by a peer that can communicate over virtio-vsock and send packets with `len == 0` and `VIRTIO_VSOCK_SEQ_EOM`. This is not ordinary remote Internet reachability, but it is adjacent reachability across the virtualization transport. In practice, the attacker is typically a local process inside a guest or on the host endpoint with access to vsock. Administrator privileges are not inherently required if vsock access is available to unprivileged processes.

Namespaces and containers may matter if vsock access is delegated into a container or sandbox. The path is configuration-dependent because virtio-vsock must be enabled and exposed, but the subsystem is common enough in virtualization deployments that it should not be treated as rare hardware-only exposure.

## 4. Severity interpretation

This behaves like an actionable Moderate resource-exhaustion issue, not an Important memory-corruption issue. The realistic impact is DoS through kernel memory/resource pressure caused by an unbounded skb receive queue. There is no concrete evidence of confidentiality impact, integrity impact, privilege escalation, UAF, OOB access, or attacker-controlled overwrite.

The paranoid score is higher because the issue can cross a guest-host style boundary and may affect virtualization infrastructure availability, but it should still remain below Strong Important because the primitive is resource exhaustion only.

## 5. One-sentence report phrase

A virtio-vsock receive accounting bug allows a vsock peer to queue many zero-length EOM skb objects without increasing payload accounting, causing resource exhaustion and denial of service on the receiving endpoint.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the issue is DoS-only but crosses a virtio-vsock guest-host boundary, and real severity depends on whether untrusted guest, container, or host processes can access vsock endpoints in the target deployment.

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

Patch: vsock/virtio: fix potential unbounded skb queue
Commit: 1eca304f97a34ed5e921e1f0e06c8b241f25bf12
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1eca304f97a34ed5e921e1f0e06c8b241f25bf12

Commit description:

virtio_transport_inc_rx_pkt() checks vvs->rx_bytes + len > vvs->buf_alloc.

virtio_transport_recv_enqueue() skips coalescing for packets
with VIRTIO_VSOCK_SEQ_EOM.

If fed with packets with len == 0 and VIRTIO_VSOCK_SEQ_EOM,
a very large number of packets can be queued
because vvs->rx_bytes stays at 0.

Fix this by estimating the skb metadata size:

	(Number of skbs in the queue) * SKB_TRUESIZE(0)

Fixes: 0777061 ("virtio/vsock: don't use skbuff state to account credit")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Stefano Garzarella <sgarzare@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Cc: "Eugenio Pérez" <eperezma@redhat.com>
Cc: virtualization@lists.linux.dev
Link: https://patch.msgid.link/20260430122653.554058-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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=1eca304f97a34ed5e921e1f0e06c8b241f25bf12

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

The original Linux kernel CVE announcement for CVE-2026-53132 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53132

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:L/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.7

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).