[CVE-2026-64523][MODERATE 7.0] net/handshake: Take a long-lived file reference at submit [ Upstream

[CVE-2026-64523][MODERATE 7.0] net/handshake: Take a long-lived file reference at submit [ Upstream

[AL-KERNEL]

CVE: CVE-2026-64523
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net/handshake: Take a long-lived file reference at submit [ Upstream
Commit: 685b10dd0e32c7782cead16c8cf055c609678583
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=685b10dd0e32c7782cead16c8cf055c609678583
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64523
Analysis date: Sat, 25 Jul 2026 14:38:13 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in net handshake can let the accept side use a request after the backing socket file has been released, creating a file or socket lifetime UAF risk that is most likely a local DoS but deserves manual review for possible higher impact.

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

The original Linux kernel CVE announcement for CVE-2026-64523 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64523

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-2026-64523	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	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-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A lifetime race in net handshake can leave the accept side with a request whose backing socket file has already been released. sock_hold keeps struct sock alive but does not keep struct socket or sock file alive, so a consumer that closes the last file reference while a handshake is pending can let sock_release tear down the socket before handshake_nl_accept_doit finishes preparing the accepted file descriptor. For the CVSS the PR:L is used for the paranoid score because a local unprivileged or reduced capability process may be able to trigger the relevant handshake consumer and close or cancel its socket while the handshake daemon is processing the request. The issue is not directly network reachable as a standalone packet path, although practical exposure depends on the protocol using net handshake and on whether remote traffic can cause pending handshakes. Impact is at least local denial of service via use after free or invalid socket lifetime, and worst case may allow confidentiality and integrity impact due to a real file or socket lifetime UAF, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	RACE ERRORPATH TEST  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	NO	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 local process may be able to create or close the relevant consumer socket while a handshake request is pending, depending on the protocol using net handshake.
* Memory corruption, weak or indirect corruption candidate: +1. The patch fixes a stale lifetime relationship where sock_hold keeps struct sock alive but not the owning struct socket or sock file.
* Real lifetime corruption: +1. This is a real file or socket lifetime bug involving missing get_file and fput synchronization.
* Reliable kernel crash or strong DoS: +1. A stale socket or file lifetime during accept side processing can plausibly lead to invalid dereference or kernel crash.
* Hard or timing dependent race: -1. The vulnerable window is between handshake_req_next and FD_PREPARE or get_file, plus concurrent close or cancel activity.
* Availability impact realistic: +1. If triggered, the effect is host kernel instability rather than a contained userspace failure.

Paranoid delta:

* Paranoid adds +1 for stronger manual review sensitivity around a real file or socket lifetime UAF in networking handshake infrastructure. This does not assume a proven LPE primitive, but keeps the issue out of auto close because stale socket file lifetime bugs can be under described in commit text.

Not awarded:

* No remote reachable +2. The affected path is not a standalone packet parsing path.
* No strong LPE +2. The patch does not show attacker controlled reclaim, writable stale object access, callback control, type confusion, or arbitrary write.
* No confidentiality or integrity impact in the conservative score. These remain theoretical without a concrete reuse or disclosure primitive.

## 3. Reachability analysis

The most realistic trigger is local and race dependent. A process or service using a kernel protocol backed by net handshake may submit a handshake request and then close or cancel the socket while the accept side is processing the request. Namespaces or reduced capability service models may matter because the relevant socket consumer could be reachable from less than full host root in some deployments. This is not directly network reachable by arbitrary packets, although remote traffic may indirectly cause pending handshakes for protocols that use this infrastructure. The path is configuration and protocol dependent, not a universal default packet path.

Call-site confidence: medium. The patch describes the concrete lifetime window and shows the file reference fix, but the exact external protocol call sites and deployment reachability are not included in the provided diff.

## 4. Severity interpretation

This behaves above an ordinary Moderate because it is a real lifetime bug involving struct socket and sock file ownership, not just a warning or resource leak. Realistic impact is most likely local denial of service through a stale pointer or invalid lifetime during handshake accept processing. Theoretical impact could be higher because file and socket lifetime UAF bugs may become exploitable if object reuse is controllable, but the provided patch does not demonstrate reclaim control, arbitrary write, or a concrete privilege escalation chain. Therefore it is best treated as Actionable Moderate at minimum, with manual review required.

## 5. One-sentence report phrase

A race in net handshake can let the accept side use a request after the backing socket file has been released, creating a file or socket lifetime UAF risk that is most likely a local DoS but deserves manual review for possible higher impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a race dependent real lifetime corruption bug involving socket and file references. Even though the conservative evidence supports DoS more strongly than LPE, the class is UAF adjacent and the patch explicitly fixes missing long lived ownership across asynchronous accept, completion, cancel, and error paths.

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

Patch: net/handshake: Take a long-lived file reference at submit [ Upstream
Commit: 685b10dd0e32c7782cead16c8cf055c609678583
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=685b10dd0e32c7782cead16c8cf055c609678583

Changed files:
  net/handshake/handshake.h
  net/handshake/netlink.c
  net/handshake/request.c
  net/sock.h

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=685b10dd0e32c7782cead16c8cf055c609678583

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

The original Linux kernel CVE announcement for CVE-2026-64523 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64523

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:L/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: 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).