[CVE-2026-90269][MODERATE REGULAR] bpf: Reject load-acquire from pointers requiring fault protection [ Upstream

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

CVE: CVE-2026-90269
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: Reject load-acquire from pointers requiring fault protection [ Upstream
Commit: c4c8de3bf48d3756ab0f910fe5cc4937d70efdcd
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c4c8de3bf48d3756ab0f910fe5cc4937d70efdcd
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90269
Analysis date: Fri, 18 Sep 2026 09:31:17 -0400
ActionableScore: 1
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-2026-90269 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90269

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-90269	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90269 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-20;CWE-754;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 verifier logic flaw allows BPF_LOAD_ACQ to read through pointer types that normally require BPF_PROBE_MEM fault protection. Unlike a regular BPF_LDX, the instruction is emitted by the JIT as a plain load without an exception table entry. A NULL or otherwise faulting pointer can therefore raise an unhandled kernel fault and panic the host. One demonstrated path reads mm from a task_struct and then applies load_acquire to mm pgd even though mm is NULL for a kernel thread. For the CVSS the PR:L value is used for the paranoid score because a restricted service account or capability limited process may be permitted to load tracing BPF programs without having complete administrative control of the host. Typical systems still require root or CAP_BPF and CAP_PERFMON, and systems with unprivileged BPF disabled have substantially lower exposure. The issue is local and is not directly reachable through network traffic. The supported impact is denial of service through a kernel panic. The analyzed path provides an invalid read but no demonstrated UAF, OOB write, information disclosure, or arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)  SKIP CVE-2026-90269 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	BPF IMPROVEONLY  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap changed either score. The BPF privilege cap is a maximum, not a scoring target.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Reliable kernel crash / strong DoS. An accepted BPF_LOAD_ACQ can become a plain JIT load without an exception-table entry, and a fault can panic the kernel.
* +0 Invalid-read concern. The established primitive is a NULL or otherwise faulting load, without useful post-fault corruption behavior.
* No remote-reachability point. Loading and attaching the tracing BPF program are local control-plane operations.
* No local-unprivileged point. The complete load, JIT, attach, and trigger sequence is not established as available to an ordinary user.
* No UAF or lifetime-corruption point. The pointer may be NULL or faulting, but no object is shown to be used after its lifetime ends.
* No authorization-bypass point. The verifier accepts an unsafe load form, but the demonstrated result is a fault rather than access to a protected resource.
* No controlled reclaim, OOB write, arbitrary write, callback influence, information disclosure, or privilege escalation is demonstrated.
* No extra Availability point. The kernel panic is already counted as the single DoS signal.
* No C or I signal. A valid load does not establish additional disclosure because equivalent fault-protected reads are already permitted for these pointer classes.
* No negative privilege point. Host-admin-equivalent privilege is not positively established, while complete below-host-admin reachability is also unresolved.
* No rarity penalty. The vulnerable instruction may be specialized, but rarity and practical inaccessibility are not both established.

3. Reachability analysis

The attacker must load and attach a tracing BPF program that uses BPF_LOAD_ACQ with an affected pointer type. The supplied example attaches to the sched_switch BTF tracepoint and obtains a NULL mm pointer from a kernel thread.

Modern systems commonly restrict this operation through CAP_BPF plus CAP_PERFMON, CAP_SYS_ADMIN, or product-specific BPF policy, and unprivileged BPF is frequently disabled. However, the supplied evidence does not establish whether the complete operation requires host-admin-equivalent authority or can be performed by a delegated BPF service account. Therefore HostAdminRequired and NamespaceScopedPrivilege remain UNKNOWN.

A network namespace alone would not provide the required BPF tracing permissions. No prior network setup, special hardware, or race is required. A supported JIT and the vulnerable BPF_LOAD_ACQ implementation are prerequisites. The x86-64 JIT behavior is demonstrated directly.

4. Primitive and severity interpretation

The exact primitive is an unprotected kernel load from a verifier-recognized fault-prone pointer. Unlike BPF_LDX converted to BPF_PROBE_MEM, BPF_LOAD_ACQ receives neither an address guard nor an exception-table recovery entry.

This is not stale storage, an active-object UAF, a repeated release, or a refcount mutation. The demonstrated consequence is a host kernel panic from a NULL or otherwise faulting dereference. No useful behavior beyond the crash is established.

PrimitiveClass is CLASS_C because the issue is a deterministic invalid-read and DoS path without an independently useful corruption or boundary-bypass primitive. ImportantCandidate is NO because neither memory corruption nor meaningful exploitation leverage beyond the crash is established. AutoDowngradeAllowed is YES because the evidence supports a privilege-gated crash-only verifier defect rather than unresolved Class A or Class B corruption.

5. One-sentence report phrase

A BPF verifier gap allows BPF_LOAD_ACQ to emit an unprotected JIT load from a fault-prone pointer, allowing an appropriately permitted local BPF program to panic the kernel without establishing memory corruption or privilege escalation.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm the product-specific BPF privilege policy and affected JIT architectures, but the supplied evidence supports only local denial of service and does not require Important-class preservation.

7. Call-site confidence

Call-site confidence: high

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

Patch: bpf: Reject load-acquire from pointers requiring fault protection [ Upstream
Commit: c4c8de3bf48d3756ab0f910fe5cc4937d70efdcd
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c4c8de3bf48d3756ab0f910fe5cc4937d70efdcd

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=c4c8de3bf48d3756ab0f910fe5cc4937d70efdcd

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

The original Linux kernel CVE announcement for CVE-2026-90269 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90269

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: unknown
  Paranoid ActionableScore: 1

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).