[CVE-2026-90138][LOW] vsock: don't check the listener's sk_err in vsock_accept() [ Upstream

[CVE-2026-90138][LOW] vsock: don't check the listener's sk_err in vsock_accept() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-90138
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: vsock: don't check the listener's sk_err in vsock_accept() [ Upstream
Commit: c5a75d37c21e558cc6fad1597e732ead30745eed
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c5a75d37c21e558cc6fad1597e732ead30745eed
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90138
Analysis date: Fri, 18 Sep 2026 00:15:59 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90138 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90138

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: LOW
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-2026-90138	LOW	https://www.kernelcve.org/list/?q=CVE-2026-90138 CHECK WITH IMPACT FROM ORIG NN LOW	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-772;CWE-404;*CWE-664;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A stale sk_err value on a listening AF_VSOCK socket can make vsock_accept reject a valid incoming connection after an earlier failed self connect on the same socket. On virtio and hyperv transports the rejected child socket may not be freed, which can leak kernel socket resources across repeated attempts. For the CVSS the PR:L is used because a local user or process must create and control AF_VSOCK sockets to trigger the sequence, but administrative privileges are not normally required. The issue is not directly network reachable and the shown trigger uses VMADDR_CID_LOCAL rather than packet traffic from an external network. Impact is denial of service through resource exhaustion. No UAF, OOB access, information leak, or privilege escalation primitive is indicated by the patch context.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	LOCK LEAK UAF IMPROVEONLY SYZBOT PACKET  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

2. Signal breakdown

Positive signals:

* +1 Concrete persistent kernel resource/reference leak. The rejected child socket is not freed on virtio and hyperv transports after accept rejects a valid connection because of stale listener sk_err.
* +1 Local unprivileged trigger. The reproducer uses ordinary AF_VSOCK socket operations and no host-admin capability is indicated.

Negative or non-awarded signals:

* RealUAF not awarded. The patch establishes a resource leak, not use-after-free or stale post-lifetime object use.
* Strong corruption not awarded. No OOB write, arbitrary write, controlled reclaim, type confusion, callback control, or refcount takeover is shown.
* Reliable kernel crash not awarded. The demonstrated impact is leaked child sockets and potential resource exhaustion, not an immediate kernel panic.
* Extra Availability not awarded. Repeated leaks may cause DoS, but the same resource-exhaustion consequence is already represented by the concrete leak signal.
* Confidentiality and Integrity not awarded. No disclosure path or unauthorized modification primitive is established.
* Remote reachability not awarded. The supplied trigger uses VMADDR_CID_LOCAL and local socket sequencing, not external network traffic.
* ImportantCandidate not set. This is a resource leak / logic bug without unresolved memory corruption or boundary-bypass leverage.

3. Reachability analysis

The trigger is a local AF_VSOCK sequence: create a listener socket, cause a failed self-connect that leaves stale sk_err, call listen, connect a second socket, and call accept. The supplied reproducer does not indicate a need for host root or host-admin-equivalent capability, so HostAdminRequired is NO.

NamespaceScopedPrivilege is UNKNOWN because no complete namespace-specific privilege chain is established or required by the supplied input. This does not affect the score because the direct local socket trigger is already below host-admin.

No prior privileged setup is established beyond having vsock support and a transport such as virtio or hyperv available. There is no special race requirement. The sequence is ordered and repeatable rather than a narrow timing race. The issue is not directly network reachable from an external IP network.

4. Primitive and severity interpretation

The exact primitive is a stale error-state logic bug that causes accept to reject a valid queued connection. On virtio and hyperv transports, that rejection leaves the child socket unfreed, creating a persistent kernel resource leak.

This is not active structured UAF and not fixed stale storage UAF. It is not a cleanup double-release or repeated refcount mutation. The demonstrated consequence is local denial of service through repeated resource leakage. A stronger consequence such as privilege escalation, information disclosure, arbitrary write, or controlled memory corruption is not supported by the patch context.

PrimitiveClass is CLASS_C because the behavior is primarily DoS/resource leakage without an independently useful corruption primitive. ImportantCandidate is NO because there is no meaningful unresolved exploitation leverage beyond resource exhaustion. AutoDowngradeAllowed is YES because this is a constrained resource leak with no UAF, no security-boundary bypass, and no concrete corruption primitive.

5. One-sentence report phrase

A stale sk_err value on a listening AF_VSOCK socket can make vsock_accept reject a valid connection and leak the rejected child socket on virtio or hyperv transports, allowing local denial of service through resource exhaustion.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the issue is a local resource leak / DoS case with no demonstrated UAF, memory corruption, information leak, privilege escalation, or security-boundary bypass.

7. Call-site confidence

Call-site confidence: high

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

Patch: vsock: don't check the listener's sk_err in vsock_accept() [ Upstream
Commit: c5a75d37c21e558cc6fad1597e732ead30745eed
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c5a75d37c21e558cc6fad1597e732ead30745eed

Changed files:
  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=c5a75d37c21e558cc6fad1597e732ead30745eed

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

The original Linux kernel CVE announcement for CVE-2026-90138 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90138

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: unknown
  Paranoid ActionableScore: 2

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).