[CVE-2026-99213][MODERATE 7.0] vsock: treat TCP_CLOSING as once-established [ Upstream

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

CVE: CVE-2026-99213
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: vsock: treat TCP_CLOSING as once-established [ Upstream
Commit: c2c5359ef2c33684fa3f3652fd761a483db8d1e7
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c2c5359ef2c33684fa3f3652fd761a483db8d1e7
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99213
Analysis date: Wed, 28 Oct 2026 23:50:00 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A vsock connect/`OP_RST` race can leave an established socket linked in `connected_table`, after which packet processing reinserts it and corrupts active kernel list state, demonstrably crashing the kernel.

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

The original Linux kernel CVE announcement for CVE-2026-99213 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99213

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-2026-99213	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99213 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-664;*CWE-787;Other CVSS 'AV:A/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.1';DESCR 'A race between vsock connect processing and an OP_RST can move a newly established socket from TCP_ESTABLISHED to TCP_CLOSING before the connect loop observes it. The old code can then reset a socket that is still present in connected_table, after which packet processing may insert the same socket again and corrupt the kernel list. The demonstrated result is a list_add double add BUG and kernel crash. Without list debugging the corrupted list links may survive until later traversal, so limited confidentiality or integrity impact is defensible and stronger memory corruption consequences require manual analysis. For the CVSS the PR:L value reflects that the attacker needs a local or virtual machine user context able to control a vsock peer or endpoint. AV:A reflects the virtual socket boundary rather than public Internet reachability, while AC:H reflects the required connect and reset race window. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7.1 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the ActionableScore threshold rule was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4. The independent weaker Aegis shadow evaluated CVSS 5.3 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	KASAN RACE LEAK  KPANIC INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 5.
* Conservative score: 5; no floor or cap applied.
* Raw paranoid score: 5.
* Paranoid score: 5; no additional effect is sufficiently proven.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 — Active kernel-object corruption: the connect/reset race leaves a socket inconsistently present in `connected_table`; later reinsertion performs list-pointer writes into already-linked active state.
* +2 — Clearly peer-network-reachable operation: an attacker controlling a local or VM-side vsock endpoint can influence the `OP_RST`/connect ordering. This is adjacent/virtual-socket reachability, not public Internet reachability.
* +1 — Reliable kernel crash/strong DoS: the supplied trace demonstrates `list_add` double-add detection, BUG, and Oops.
* No extra Availability point: it would duplicate the demonstrated crash.
* No UAF, controlled reclaim, arbitrary target/payload, disclosure, LPE, or authorization bypass is shown.
* No C/I point: list corruption without list debugging is credible, but useful confidentiality or protected-state modification is unresolved.
* No race penalty: the race window is required, but the evidence does not establish a one-shot or materially uncontrollable race.
* B5-R and B3-PENDING do not apply: there is neither retry-accumulated heap OOB nor shared-backing modification.

3. Reachability analysis

The grounded attacker is a below-host-administrator actor able to operate a vsock endpoint or control its peer and race connection establishment with `OP_RST`. No host UID 0 or host capability requirement is evidenced. The complete trigger is not shown to depend on user/net namespaces, so namespace-scoped privilege remains unknown. No unusual hardware or separate privileged setup is identified. Guest-to-host impact is credible as a review boundary for VM-facing vsock, but the evidence does not prove that every trigger is guest-only or that host state beyond the affected kernel list is compromised.

4. Primitive and severity reading

The primitive is an attacker-influenced inconsistency in active structured socket-table state, followed by kernel packet processing reinserting the socket and writing corrupted list links. This is CLASS_B active-object/list corruption, not a fixed stale buffer, UAF, or cleanup-only fault. The demonstrated effect is a host kernel Oops when list debugging detects the double insertion. Without that guard, malformed links may remain active and be consumed by later table operations, but directed writes, controlled traversal, disclosure, and privilege escalation are unproven.

ImportantCandidate is YES under the active-state/trust-boundary rule: the corrupt write, privileged kernel consumer, and credible vsock guest/local-peer boundary are separately grounded, while downstream leverage remains unknown. Auto-downgrade is therefore unsafe.

5. One-sentence report phrase

A vsock connect/`OP_RST` race can leave an established socket linked in `connected_table`, after which packet processing reinserts it and corrupts active kernel list state, demonstrably crashing the kernel.

6. Manual review advice

MANUAL CHECK REQUIRED

Review non-debug list behavior, subsequent table traversal, and whether a guest-controlled endpoint can produce useful host-kernel corruption beyond the demonstrated crash.

7. Call-site confidence

Call-site confidence: high

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

Patch: vsock: treat TCP_CLOSING as once-established [ Upstream
Commit: c2c5359ef2c33684fa3f3652fd761a483db8d1e7
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c2c5359ef2c33684fa3f3652fd761a483db8d1e7

Changed files:
  lib/list_debug.c
  net/vmw_vsock/af_vsock.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=c2c5359ef2c33684fa3f3652fd761a483db8d1e7

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

The original Linux kernel CVE announcement for CVE-2026-99213 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99213

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:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.1

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: unknown
  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).