[CVE-2026-64353][MODERATE REGULAR] bpf: Keep dynamic inner array lookups nullable [ Upstream

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

CVE: CVE-2026-64353
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: Keep dynamic inner array lookups nullable [ Upstream
Commit: 0b92ad64d6e4bde85e6b9888404f9a7a2b65d269
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b92ad64d6e4bde85e6b9888404f9a7a2b65d269
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64353
Analysis date: Sat, 25 Jul 2026 05:45:32 -0400
ActionableScore: 4
ActionableScore lower bound: 1
Actionable bucket: Borderline manual review recommended
Manual review required: YES

Summary:
A BPF verifier nullness-elision bug for ARRAY_OF_MAPS inner templates can allow a crafted local BPF program to dereference a runtime NULL map value pointer, causing a kernel crash, with practical reachability depending on whether BPF loading is privileged or delegated.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64353 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64353

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 REGULAR
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-2026-64353	MODERATE	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-476;CWE-754;*CWE-20;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A BPF verifier unsoundness occurs for ARRAY_OF_MAPS with an inner array template marked BPF_F_INNER_MAP. The verifier can remove PTR_MAYBE_NULL from a const-key map lookup by checking the template max_entries, while the runtime lookup uses the concrete inner map max_entries and can still return NULL. A crafted local BPF program can then dereference a value pointer that the verifier treats as non-null, causing a kernel NULL-pointer dereference and denial of service. For the CVSS the PR:L is used for the paranoid score because a local user or service with permission to create BPF maps and load BPF programs can trigger this in delegated BPF environments without full root privileges. The issue is not network reachable. Impact is local denial of service via kernel crash. No direct arbitrary read or arbitrary write primitive is visible from this patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended (with actual score 3)  SKIP CVE-2026-64353 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: d2102f2f5d75a84dbab6ff890359f0bd4a18ca22 YES  NO NO unknown 	MAYBE	BPF SIMPLEFIX HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1. The verifier can incorrectly treat a lookup result as non-NULL, while runtime may return NULL, enabling a kernel NULL-pointer dereference.
* Broad/default/common subsystem: +1. BPF verifier bugs are security-sensitive and affect a broadly present kernel subsystem.
* Requires admin/root/CAP_* in typical deployments: -2. In the evaluated configuration, BPF loading is privileged and unprivileged BPF is disabled by default.

Conservative total: 1.

Paranoid signals:

* Local unprivileged or reduced-privilege trigger: +1. In delegated BPF environments, a local service account or reduced-capability user with BPF permissions may trigger it without full host-root.
* Local high-control kernel data-plane API: +1. BPF gives fine-grained control over verifier state and map lookup patterns, but this applies only in the paranoid delegated-access interpretation.
* Reliable kernel crash / strong DoS: +1. The direct demonstrated impact is a NULL-pointer dereference and kernel crash.
* Broad/default/common subsystem: +1. BPF verifier correctness bugs deserve manual scrutiny even when privileged-gated.

Paranoid total: 4.

Not awarded:

* No generic strong memory corruption. The patch supports a NULL dereference, not UAF, OOB write, arbitrary write, refcount takeover, or type confusion.
* No privilege escalation bonus. No reclaim, controlled replacement, callback control, or write primitive is shown.
* No confidentiality or integrity impact. The visible primitive is DoS only.

## 3. Reachability analysis

Typical triggering requires creating BPF maps and loading a crafted BPF program that uses ARRAY_OF_MAPS with an inner array template marked BPF_F_INNER_MAP. In normal hardened product configurations, this requires CAP_BPF, CAP_SYS_ADMIN, or equivalent privileged BPF access, so the conservative score treats it as privileged local. Namespaces or delegated BPF setups can reduce the practical privilege barrier, but that is configuration-dependent. The issue is not network reachable.

## 4. Severity interpretation

This behaves like a privileged or delegated-local BPF verifier DoS, not an Important-class LPE based on the provided patch. The theoretical concern is verifier unsoundness, which is historically sensitive, but the concrete primitive shown here is NULL-pointer dereference after incorrect nullness elision. Realistic exploitation evidence supports kernel crash only, while privilege escalation is not demonstrated.

## 5. One-sentence report phrase

A BPF verifier nullness-elision bug for ARRAY_OF_MAPS inner templates can allow a crafted local BPF program to dereference a runtime NULL map value pointer, causing a kernel crash, with practical reachability depending on whether BPF loading is privileged or delegated.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED.

Reason: BPF verifier soundness bugs should not be auto-closed purely from the DoS-looking patch, but the current evidence does not justify Important severity because no LPE, arbitrary read/write, UAF reclaim, or object replacement primitive is shown.

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

Patch: bpf: Keep dynamic inner array lookups nullable [ Upstream
Commit: 0b92ad64d6e4bde85e6b9888404f9a7a2b65d269
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0b92ad64d6e4bde85e6b9888404f9a7a2b65d269

Changed files:
  kernel/bpf/verifier.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=0b92ad64d6e4bde85e6b9888404f9a7a2b65d269

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

The original Linux kernel CVE announcement for CVE-2026-64353 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64353

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:H/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: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: 1
  Paranoid ActionableScore: 4

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).