[CVE-2026-52994][MODERATE REGULAR] vsock/virtio: fix MSG_ZEROCOPY pinned-pages accounting [ Upstream

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

CVE: CVE-2026-52994
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: vsock/virtio: fix MSG_ZEROCOPY pinned-pages accounting [ Upstream
Commit: 6af1736b5810bc8a4a43a8518530113f5a757dc1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6af1736b5810bc8a4a43a8518530113f5a757dc1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52994
Analysis date: Thu, 25 Jun 2026 11:05:28 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / borderline actionable resource-exhaustion issue
Manual review required: NO

Summary:
virtio vsock MSG_ZEROCOPY used an already consumed iterator size for pinned-pages accounting, allowing a local sender to bypass RLIMIT_MEMLOCK enforcement and potentially cause resource-exhaustion DoS.

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

The original Linux kernel CVE announcement for CVE-2026-52994 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52994

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.

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

CVE-2026-52994	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-770;**CWE-400;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 'virtio vsock MSG_ZEROCOPY accounting can use an already consumed iov iterator when allocating zerocopy completion state, so the size passed to pinned page accounting may become 0 on the last skb. This can bypass RLIMIT_MEMLOCK enforcement for pinned pages and allow a local sender to consume more locked memory than intended. For the CVSS the PR:L is used because a local user process is required to create a vsock sender and issue MSG_ZEROCOPY sends, but administrative privileges are not normally required for the vulnerable send path. The issue is not directly network reachable and affects the local kernel that performs the send and page pinning. Impact is denial of service through memory pressure or resource exhaustion, with no supported confidentiality or integrity impact because the patch shows an accounting error rather than UAF, OOB access, or arbitrary write.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / borderline actionable resource-exhaustion issue (with actual score 3) 	MAYBE	VIRT SIMPLEFIX SKB 	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / borderline actionable resource-exhaustion issue**

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local process able to use virtio vsock and MSG_ZEROCOPY can reach the affected send path.
* Cross-boundary isolation/policy bypass: +1
  The bug bypasses RLIMIT_MEMLOCK pinned-pages accounting, which is an intended per-process resource-control boundary.

Paranoid additional signal:

* Availability impact realistic: +1
  Sustained abuse may allow more pinned memory than intended and create memory pressure or resource exhaustion. This is still DoS/resource exhaustion, not memory corruption.

Signals not applied:

* Remote reachable: +0
  This is not a normal network-remote attack path. It requires local code execution in the affected kernel context.
* Generic memory corruption: +0
  The patch shows an accounting-size bug, not UAF, OOB write, double-free, or object confusion.
* Privilege escalation plausible: +0
  No credible privilege-escalation primitive is supported by the diff.
* Strong DoS / reliable crash: +0 conservative
  The bug can contribute to memory pressure, but the patch does not show a single-shot reliable crash primitive.

## 3. Reachability analysis

The likely trigger is a local user process using AF_VSOCK with MSG_ZEROCOPY on a system where virtio vsock zerocopy support is enabled. Administrative privileges are not normally required for the vulnerable send path, so PR is effectively local user level rather than root.

Namespaces and containers may matter if untrusted workloads are allowed to use vsock. In that case, the issue can become more relevant as a resource-limit bypass affecting other workloads or the host-backed memory budget. It is not directly Internet reachable and depends on virtio vsock deployment, commonly in virtualized environments.

## 4. Severity interpretation

This behaves like an ordinary Moderate resource-accounting vulnerability, with a borderline actionable angle because it bypasses RLIMIT_MEMLOCK enforcement. The realistic impact is local denial of service through pinned-page or memory-pressure abuse.

Theoretical memory-corruption impact is not supported. The patch only changes the size passed to msg_zerocopy_realloc() for accounting, and does not indicate stale pointers, attacker-controlled overwrites, page-cache corruption, or lifetime corruption.

## 5. One-sentence report phrase

virtio vsock MSG_ZEROCOPY used an already consumed iterator size for pinned-pages accounting, allowing a local sender to bypass RLIMIT_MEMLOCK enforcement and potentially cause resource-exhaustion DoS.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a resource-accounting and DoS-only issue without evidence of memory corruption, privilege escalation, or remote reachability. It can be handled as ordinary Moderate unless the product threat model treats untrusted vsock users or containerized workloads as high-risk.

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

Patch: vsock/virtio: fix MSG_ZEROCOPY pinned-pages accounting [ Upstream
Commit: 6af1736b5810bc8a4a43a8518530113f5a757dc1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=6af1736b5810bc8a4a43a8518530113f5a757dc1

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=6af1736b5810bc8a4a43a8518530113f5a757dc1

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

The original Linux kernel CVE announcement for CVE-2026-52994 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52994

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).