[CVE-2026-63978][MODERATE 7.0] net/handshake: Drain pending requests at net namespace exit [ Upstream

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

CVE: CVE-2026-63978
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net/handshake: Drain pending requests at net namespace exit [ Upstream
Commit: 9ec20c9a5a04f2c3f1cf65d21f886d7aaa6189cd
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9ec20c9a5a04f2c3f1cf65d21f886d7aaa6189cd
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63978
Analysis date: Sun, 19 Jul 2026 20:39:35 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in net/handshake namespace-exit draining can leave pending handshake requests concurrently cancelled or freed while still linked on the drain list, causing list corruption or UAF and making this an Actionable Moderate issue with manual review required.

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

The original Linux kernel CVE announcement for CVE-2026-63978 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63978

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-63978	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-362;*CWE-416;*CWE-772;*CWE-401;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'net handshake net namespace exit can leave pending handshake requests linked while concurrent cancellation or timeout runs against the same request. The original drain path could fail to move pending requests off hn_requests and later fixes reveal a race where remove_pending can delete an entry from the drain scratch list or operate after LIST_POISON. A cancel path can also drop the last hr_file reference while the drain loop still owns the list entry, so the request may be freed while still linked and later used by the drain. For the CVSS the PR:L is used because practical triggering needs local code execution or a local service context able to create or tear down a net namespace and cause pending handshake requests, but it does not necessarily require full host root in namespace enabled or delegated container setups. The issue is not directly network reachable by packet traffic alone. Impact is at least local denial of service via list corruption or kernel crash and in the worst case may allow confidentiality or integrity impact due to a UAF candidate that should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5)	YES	DANGER INIT RACE IMPROVEONLY TEST  KPANIC INCREASED_TO_MODERATE7_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: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local trigger: +1. Triggering appears to require local control over a net namespace lifecycle or a local service context that can create pending handshake requests.
* Memory corruption, weak primitive: +1. The patch describes list corruption and a request that may be freed while still linked, but no attacker-controlled reclaim or overwrite primitive is shown.
* Real lifetime corruption: +1. The commit explicitly describes an hr_file reference drop allowing sk_destruct to free the request while the drain loop still owns the list entry.
* Reliable kernel crash / strong DoS: +1. LIST_POISON, corrupted list traversal, or UAF during drain can plausibly crash the kernel.
* Cross-boundary namespace impact: +1. A namespace teardown path can affect the host kernel, relevant for containerized or delegated namespace environments.
* Hard timing/race requirement: -1. The dangerous case depends on concurrent drain and cancel/timeout behavior.

Paranoid adjustment:

* The race path is concrete in the commit message, involving netns drain plus concurrent handshake_req_cancel or timeout. For triage sensitivity, the paranoid score does not subtract the race point, but remains capped at 5 because no controlled reclaim, callback hijack, arbitrary write, or demonstrated LPE primitive is shown.

Not counted:

* Remote reachable: +0. This is not directly triggerable by network packets alone.
* Strong LPE plausibility: +0. UAF exists as a candidate, but no reclaim or controlled object replacement is demonstrated.
* Confidentiality / integrity impact: +0 for conservative scoring. The patch supports UAF concern, but not a concrete read or write primitive.

## 3. Reachability analysis

The likely attacker is local or container-adjacent, not remote. Practical triggering requires pending net/handshake requests, net namespace exit, and a concurrent cancel or timeout path such as the SUNRPC TLS timeout case mentioned in the commit. Full host root is not necessarily required in all deployments because namespace-enabled or delegated container environments may allow reduced-privilege actors to influence net namespace teardown, but typical bare-metal triggering may still require elevated local control. The affected path is not a central packet receive path and is not public-Internet reachable by itself.

## 4. Severity interpretation

This is more serious than an ordinary resource leak because the corrected drain path exposes list corruption and request lifetime corruption. Realistic demonstrated impact is local DoS via kernel crash or corrupted list traversal. Theoretical escalation concern exists because the request can be freed while still linked, but the patch does not show attacker-controlled reuse, overwrite, callback dispatch, or type confusion. Therefore the practical result is Actionable Moderate, with manual review needed to decide whether it rises to Important.

## 5. One-sentence report phrase

A race in net/handshake namespace-exit draining can leave pending handshake requests concurrently cancelled or freed while still linked on the drain list, causing list corruption or UAF and making this an Actionable Moderate issue with manual review required.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch contains an explicit lifetime bug plus list corruption plus a UAF candidate during namespace teardown. Even though the realistic impact is likely local DoS and the race is timing-dependent, this should not be auto-closed without checking whether request reuse or controlled reclaim is possible.

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

Patch: net/handshake: Drain pending requests at net namespace exit [ Upstream
Commit: 9ec20c9a5a04f2c3f1cf65d21f886d7aaa6189cd
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9ec20c9a5a04f2c3f1cf65d21f886d7aaa6189cd

Changed files:
  net/handshake/netlink.c
  net/handshake/request.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=9ec20c9a5a04f2c3f1cf65d21f886d7aaa6189cd

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

The original Linux kernel CVE announcement for CVE-2026-63978 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-63978

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:L/I:L/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).