[CVE-2026-74613][MODERATE 7.0] vsock/virtio: avoid refilling the RX queue after teardown

[CVE-2026-74613][MODERATE 7.0] vsock/virtio: avoid refilling the RX queue after teardown

[AL-KERNEL]

CVE: CVE-2026-74613
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: vsock/virtio: avoid refilling the RX queue after teardown
Commit: a7658508f5fe8f1077a65e8cb9535d3426f37a2f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a7658508f5fe8f1077a65e8cb9535d3426f37a2f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74613
Analysis date: Sat, 22 Aug 2026 17:04:05 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in virtio-vsock RX teardown can allow queued RX work to refill a deleted virtqueue, causing a slab use-after-free in `virtqueue_add_sgs()` and a kernel crash, with practical exploitation depending on virtio-vsock activity overlapping VM or device teardown.

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

The original Linux kernel CVE announcement for CVE-2026-74613 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74613

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-74613	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in virtio vsock RX teardown can let virtio_transport_rx_work refill the RX queue after rx_run is cleared and after the virtqueues have been deleted. This reaches virtqueue_add_sgs on a freed virtqueue object and KASAN reports a slab use after free. For the CVSS the PR:L is used in the paranoid score because an unprivileged local user may be able to generate vsock activity while teardown is performed by the local system or virtualization control path, although reliable triggering normally depends on a narrow race window. The issue is not a normal remote network attack and is mainly relevant to systems using virtio vsock in virtualized environments. Impact is at least denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to use after free memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	READ DANGER VIRT UAF HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Memory corruption, weak primitive: +1
  KASAN shows a real slab use after free in `virtqueue_add_sgs`, but the patch only shows stale virtqueue use after teardown, not attacker controlled reclaim or overwrite.
* Real lifetime corruption: +1
  The RX worker can run after `virtio_vsock_vqs_del()` deleted the virtqueues.
* Reliable kernel crash / strong DoS: +1
  The report shows KASAN slab UAF and kernel panic with `panic_on_warn`.
* Privileged kernel/device-management memory corruption path: +1
  The bug occurs in virtio/vsock teardown and virtqueue management, a trusted device-management path.
* Hard or unreliable race / special timing required: -1
  The trigger depends on queued RX work overlapping device freeze/remove/teardown.
* Requires admin/root/device lifecycle control in typical deployments: -1
  Reliable triggering normally requires suspend/freeze/remove or virtio device lifecycle control, although not necessarily full host-root in all virtualization models.

Paranoid additional signal:

* Local unprivileged trigger component: +1
  A local guest user may be able to generate AF_VSOCK RX activity and keep the worker path active while teardown is performed by VM lifecycle management or another privileged path.

Not awarded:

* Remote reachable: +0
  This is not ordinary IP network reachable. It is mainly virtio-vsock and VM lifecycle dependent.
* Strong LPE plausibility: +0
  No controlled reclaim, attacker-chosen replacement object, callback control, write-after-free, refcount takeover, or arbitrary write is shown.
* Confidentiality / integrity impact: +0 conservative
  The concrete evidence is UAF read/crash, not a demonstrated leak or write primitive. Paranoid CVSS may still flag CIA risk for manual review, but ActionableScore should not double-count unsupported exploitability.

## 3. Reachability analysis

The affected path is in `virtio_transport_rx_work()` for virtio-vsock. A worker queued before or during teardown can reach the common exit path and call `virtio_vsock_rx_fill()` even after `rx_run` is false and the virtqueues have been deleted.

Typical reliable triggering requires a virtio-vsock enabled guest and a teardown event such as virtio device freeze, suspend, remove, or VM lifecycle transition. Ordinary local users may be able to create vsock activity, but they usually cannot directly initiate the teardown path. Containers and namespaces do not obviously make the teardown path unprivileged, although delegated virtualization or service-control models could reduce the effective privilege boundary.

The path is not public Internet reachable. It is relevant mainly to virtualized systems using virtio-vsock.

Call-site confidence: high. The commit includes the changed function, the failing call trace, and the free path.

## 4. Severity interpretation

This is more than an ordinary low-risk cleanup because the bug is a confirmed lifetime error with KASAN slab use after free in a kernel virtqueue path. Realistically, the demonstrated impact is a race-dependent local or lifecycle-mediated kernel crash. Theoretical escalation risk exists because this is a real UAF, but the patch does not show attacker-controlled reclaim, write-after-free, type confusion, callback dispatch, or refcount takeover.

Overall this should be treated as Actionable Moderate at minimum, not auto-closed. It is below a strong Important classification unless additional evidence shows unprivileged reliable triggering or a usable UAF exploitation primitive.

## 5. One-sentence report phrase

A race in virtio-vsock RX teardown can allow queued RX work to refill a deleted virtqueue, causing a slab use-after-free in `virtqueue_add_sgs()` and a kernel crash, with practical exploitation depending on virtio-vsock activity overlapping VM or device teardown.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: confirmed UAF in a virtqueue/device lifetime path. The currently shown primitive is mostly DoS, but memory lifetime bugs in virtio teardown paths deserve manual review to confirm whether unprivileged guest activity can reliably shape timing or reclaim behavior.

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

Patch: vsock/virtio: avoid refilling the RX queue after teardown
Commit: a7658508f5fe8f1077a65e8cb9535d3426f37a2f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a7658508f5fe8f1077a65e8cb9535d3426f37a2f

Commit description:

Commit b917507 ("vsock/virtio: stop workers during the .remove()")
made the RX worker jump to its common exit when rx_run is clear.  That
exit still refills the RX queue when the buffer count is low, so work
queued across virtio_vsock_vqs_del() can add buffers after the virtqueues
have been deleted.

BUG: KASAN: slab-use-after-free in virtqueue_add_sgs
Read of size 4 by task kworker/0:1
Workqueue: virtio_vsock virtio_transport_rx_work
Call Trace:
 virtqueue_add_sgs (drivers/virtio/virtio_ring.c:2796)
 virtio_vsock_rx_fill (net/vmw_vsock/virtio_transport.c:332)
 virtio_transport_rx_work (net/vmw_vsock/virtio_transport.c:701)
 process_one_work (kernel/workqueue.c:3314)
 worker_thread (kernel/workqueue.c:3478)
 kthread (kernel/kthread.c:436)
 ret_from_fork (arch/x86/kernel/process.c:158)
 ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
...
Freed by task 141:
 kfree (mm/slub.c:6566)
 vp_del_vq (drivers/virtio/virtio_pci_common.c:259)
 vp_del_vqs (drivers/virtio/virtio_pci_common.c:285)
 virtio_vsock_freeze (net/vmw_vsock/virtio_transport.c:912)
 virtio_device_freeze (drivers/virtio/virtio.c:658)
 virtio_pci_freeze (drivers/virtio/virtio_pci_common.c:601)
 pci_pm_freeze (drivers/pci/pci-driver.c:1098)
 device_suspend (drivers/base/power/main.c:1968)
Kernel panic - not syncing: KASAN: panic_on_warn set ...

Jump to a no-refill exit when rx_run is clear, leaving the normal exit
to replenish a running queue.

Fixes: b917507 ("vsock/virtio: stop workers during the .remove()")
Cc: stable@vger.kernel.org
Reported-by: Xiang Mei <xmei5@asu.edu>
Link: https://lore.kernel.org/r/20260727035804.1860862-1-bestswngs@gmail.com
Suggested-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Reviewed-by: Bobby Eshleman <bobbyeshleman@meta.com>
Link: https://patch.msgid.link/f9c8c1d64cad9d262f305d02ffe164c2f900fadf.1785352330.git.bestswngs@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/virtio/virtio_ring.c
  net/vmw_vsock/virtio_transport.c
  kernel/workqueue.c
  kernel/kthread.c
  arch/x86/kernel/process.c
  arch/x86/entry/entry_64.S
  mm/slub.c
  drivers/virtio/virtio_pci_common.c
  drivers/virtio/virtio.c
  drivers/pci/pci-driver.c
  drivers/base/power/main.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=a7658508f5fe8f1077a65e8cb9535d3426f37a2f

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

The original Linux kernel CVE announcement for CVE-2026-74613 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74613

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:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 3
  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: NO
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).