[CVE-2026-64115][IMPORTANT] vsock/vmci: fix UAF when peer resets connection during handshake

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

CVE: CVE-2026-64115
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: vsock/vmci: fix UAF when peer resets connection during handshake
Commit: 1e19f08552b90070ed18bafb1763c78297823af6
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1e19f08552b90070ed18bafb1763c78297823af6
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64115
Analysis date: Sun, 19 Jul 2026 22:43:59 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A VMCI/VSOCK peer RST during server-side handshake can leave a pending socket linked after its lifetime is ending, causing delayed cleanup to perform a write-after-free in the socket refcount path and crash the kernel.

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

The original Linux kernel CVE announcement for CVE-2026-64115 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64115

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: IMPORTANT
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-2026-64115	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A use-after-free can occur in the VMCI/VSOCK server handshake path when a peer RST is treated as success and the pending socket remains linked after it has moved toward TCP_CLOSE. The delayed vsock_pending_work can later perform cleanup as if the socket were still pending, where the first sock_put may free the socket and a following sock_put writes into the freed object. For the CVSS the PR:N is used because the vulnerable side can be reached by a VMCI/VSOCK peer during connection handling and no privileges on the victim kernel are required beyond access to the exposed VSOCK service. The attack vector is adjacent rather than Internet remote because VMCI/VSOCK is normally limited to guest host or same virtualization fabric communication. Impact is at least denial of service via kernel crash, and the paranoid score treats the freed socket write as a memory corruption primitive that may allow confidentiality and integrity impact in worst case.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	DANGER RACE UAF LINUS KPANIC PACKET  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

* Adjacent VMCI/VSOCK peer influence: +1
  Not Internet remote, but triggerable by a VMCI/VSOCK peer in a virtualization communication context.

* Memory corruption, strong corruption primitive: +2
  The commit explicitly reports slab-use-after-free and a write into a freed socket object via `sock_put()` / refcount path.

* Real lifetime corruption: +1
  Pending socket lifetime is mishandled. The object remains on `pending_links` after the destroy path drops a reference.

* Weak LPE concern: +1
  UAF write exists, but no attacker-controlled reclaim, object replacement, type confusion, callback control, or arbitrary write is shown.

* Reliable kernel crash / strong DoS: +1
  KASAN reproducer shows 52/100 failures unpatched and 0/100 patched.

* Availability impact realistic: +1 for paranoid score
  The crash appears reproducible and host-kernel-wide in the affected VSOCK/VMCI path. This is counted only in the paranoid score to avoid over-counting DoS.

No subtraction for hard race: the issue is timing-dependent, but the provided KASAN testing indicates realistic reproducibility.

## 3. Reachability analysis

The bug can be triggered by a VMCI/VSOCK peer during connection handshake handling by sending a peer RST at the wrong state. This is adjacent rather than normal network remote exposure because VMCI/VSOCK is usually scoped to guest-host or virtualization-fabric communication.

Privileges on the victim kernel are not required if the attacker can reach the exposed VSOCK service as a peer. In container or VM environments, practical reachability depends on whether VSOCK/VMCI endpoints are exposed to less-trusted guests or services.

The path is not universally default-exposed like TCP/IP, but it is relevant in VMware or VSOCK-enabled virtualization deployments.

Call-site confidence: high. The commit describes the caller consequence through `vmci_transport_recv_listen()`, `vsock_remove_pending()`, delayed `vsock_pending_work()`, and trailing `sock_put()` behavior.

## 4. Severity interpretation

This is not an ordinary Moderate cleanup bug. It is a confirmed lifetime bug with UAF write-after-free behavior in a socket object and a reproducible kernel crash.

Realistic demonstrated impact is DoS. Theoretical higher impact is plausible because the primitive is a real UAF write into freed kernel memory, but the patch does not show controlled reclaim or arbitrary write. Therefore the conservative result is Actionable Moderate, while the paranoid result reaches Strong Important candidate for manual review.

## 5. One-sentence report phrase

A VMCI/VSOCK peer RST during server-side handshake can leave a pending socket linked after its lifetime is ending, causing delayed cleanup to perform a write-after-free in the socket refcount path and crash the kernel.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: confirmed UAF write-after-free plus realistic adjacent peer triggering and reproducible KASAN crashes make this unsuitable for auto-close, even though practical privilege escalation is not demonstrated.

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

Patch: vsock/vmci: fix UAF when peer resets connection during handshake
Commit: 1e19f08552b90070ed18bafb1763c78297823af6
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1e19f08552b90070ed18bafb1763c78297823af6

Commit description:

vmci_transport_recv_connecting_server() returned err = 0 for a peer
RST in its default switch arm:

	err = pkt->type == VMCI_TRANSPORT_PACKET_TYPE_RST ? 0 : -EINVAL;

That made vmci_transport_recv_listen() skip vsock_remove_pending(),
leaving the pending socket on the listener's pending_links with
sk_state = TCP_CLOSE while destroy: still dropped the explicit
reference taken before schedule_delayed_work().

One second later vsock_pending_work() observed is_pending=true and
performed full cleanup: vsock_remove_pending() then the two trailing
sock_put(sk) calls -- the first reached refcount 0 and __sk_freed
the socket, and the second wrote into the freed object:

  BUG: KASAN: slab-use-after-free in refcount_warn_saturate
  Write of size 4 at addr ffff88800b1cac80 by task kworker
  Workqueue: events vsock_pending_work

Treat peer RST like any other unexpected packet type (err = -EINVAL).
All destroy: arms now return err < 0, so vmci_transport_recv_listen()
removes pending from pending_links synchronously and
vsock_pending_work() takes the is_pending=false / !rejected branch,
dropping only its own work reference.  This also closes the
multi-packet race Sashiko reported on v2: pending is removed from
the list before any subsequent packet can find it.

The pre-existing sk_acceptq_removed() gap on the err < 0 path of
vmci_transport_recv_listen() that Sashiko also noted is not
introduced or changed by this patch.

Tested on lts-6.12.79 with KASAN: 52/100 unpatched -> 0/100 patched.

Fixes: d021c34 ("VSOCK: Introduce VM Sockets")
Cc: stable@vger.kernel.org
Signed-off-by: Minh Nguyen <minhnguyen.080505@gmail.com>
Acked-by: Bryan Tan <bryan-bt.tan@broadcom.com>
Link: https://patch.msgid.link/20260519102310.237181-1-minhnguyen.080505@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/vmw_vsock/vmci_transport.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=1e19f08552b90070ed18bafb1763c78297823af6

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

The original Linux kernel CVE announcement for CVE-2026-64115 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64115

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 6
  Paranoid ActionableScore: 7

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).