[CVE-2026-53031][MODERATE 7.0] bpf: Validate node_id in arena_alloc_pages() [ Upstream

[CVE-2026-53031][MODERATE 7.0] bpf: Validate node_id in arena_alloc_pages() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-53031
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Validate node_id in arena_alloc_pages() [ Upstream
Commit: 31d3b4b28e55835646d6829d60023f730dd34e85
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=31d3b4b28e55835646d6829d60023f730dd34e85
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53031
Analysis date: Thu, 25 Jun 2026 10:15:22 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
Missing validation of an attacker supplied BPF arena NUMA node ID can send invalid or offline node values into the kernel allocation path, causing local DoS and requiring manual review for possible allocator-internal corruption impact.

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

The original Linux kernel CVE announcement for CVE-2026-53031 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53031

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
======================================================================

CVE-2026-53031	MODERATE	CHECK	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-129;*CWE-20;*CWE-787;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.8';DESCR 'arena_alloc_pages accepts an attacker controlled node_id and passed it into the NUMA allocation path without validating the node range or online state. A local user with the ability to create and use BPF arena can supply an invalid or offline node id, which may make the kernel allocation path index invalid NUMA node data and crash. For the CVSS the PR:L is used for the paranoid score because triggering requires local BPF capability or an environment where BPF use is delegated to a less privileged service or user, but it does not require full host root in all deployments. The issue is not network reachable. Base impact is local denial of service via kernel crash. In the paranoid interpretation, invalid NUMA node indexing in the page allocator path is a memory corruption candidate, so confidentiality and integrity impact may be possible and the issue should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5) 	MAYBE	OOB BPF SIMPLEFIX LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	-	-	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:

* Weak or indirect corruption candidate: +1. `node_id` is attacker influenced through the BPF arena allocation path and was passed into NUMA/page allocation without range or online-node validation.
* Weak LPE concern: +1. Invalid NUMA node selection may reach allocator internals, but the patch does not show a controlled write, reclaim primitive, UAF, or object-confusion primitive.
* Reliable kernel crash / strong DoS: +1. Invalid or offline node IDs can plausibly lead to allocator faults, WARN/BUG paths, NULL dereference, or invalid per-node data access.
* Local high-control kernel data-plane API: +1. BPF arena is a rich local kernel API where users can shape allocation requests.
* Broad/common subsystem exposure: +1. BPF is widely deployed, although BPF arena use is more specialized and typically gated.
* Capability-gated local access: -1. Triggering usually requires BPF privileges such as CAP_BPF/CAP_SYS_ADMIN or a delegated BPF-capable service context, so this is not ordinary unprivileged local access.

Paranoid additional interpretation:

* Privileged allocator-internal sink: +1. The unchecked value enters trusted NUMA/page allocator paths, so manual review is justified even without a demonstrated exploit primitive.

## 3. Reachability analysis

The bug is local only. It is not network reachable. A realistic trigger requires the ability to create and use BPF arena functionality, which is normally restricted by BPF capability policy or by privileged service/container configuration. Namespaces and delegated BPF setups matter because a reduced-capability service, container root, or user with BPF access may be below full host root but still able to reach this path. The affected subsystem is not a default unauthenticated interface, but BPF is common enough that the issue should not be treated as rare hardware-only or unreachable.

## 4. Severity interpretation

This is more than an ordinary low-priority DoS because unchecked `node_id` flows into allocator internals from a high-control BPF API. The realistic impact is local kernel crash or allocator failure. The theoretical escalation concern is weaker than a proven UAF/OOB write because there is no clear attacker-controlled overwrite target or payload in the patch. Therefore this fits Actionable Moderate rather than automatic Important, with manual review recommended to confirm whether invalid NUMA node handling can become memory corruption beyond crash.

## 5. One-sentence report phrase

Missing validation of an attacker supplied BPF arena NUMA node ID can send invalid or offline node values into the kernel allocation path, causing local DoS and requiring manual review for possible allocator-internal corruption impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug is reachable through BPF arena and affects allocator/NUMA internals. The demonstrated impact is likely DoS, but the invalid-index path is serious enough to verify whether it can produce memory corruption or privilege escalation in affected kernel configurations.

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

Patch: bpf: Validate node_id in arena_alloc_pages() [ Upstream
Commit: 31d3b4b28e55835646d6829d60023f730dd34e85
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=31d3b4b28e55835646d6829d60023f730dd34e85

Changed files:
  kernel/bpf/arena.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=31d3b4b28e55835646d6829d60023f730dd34e85

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

The original Linux kernel CVE announcement for CVE-2026-53031 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53031

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:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.8

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).