[CVE-2026-92515][LOW] bpf: Preserve unique-field state across nested structs [ Upstream

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

CVE: CVE-2026-92515
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: bpf: Preserve unique-field state across nested structs [ Upstream
Commit: cec97102d4147e18568c93946014c4c8ebf86fcf
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cec97102d4147e18568c93946014c4c8ebf86fcf
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92515
Analysis date: Fri, 18 Sep 2026 09:07:46 -0400
ActionableScore: 2
ActionableScore lower bound: 1
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-2026-92515 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92515

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-2026-92515	LOW	https://www.kernelcve.org/list/?q=CVE-2026-92515 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-20;CWE-617;CWE-703;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 crafted user BTF can place duplicate unique special fields at different nesting levels because btf_find_struct_field used a fresh seen mask during recursive traversal. The duplicate fields can later reach btf_parse_fields and trigger an invariant WARN_ON_ONCE before later map creation capability checks. For the CVSS the PR:L is used because a local user or local process must be able to submit user supplied BTF through the BPF/BTF interface, while no remote network path is involved. Impact is primarily a local denial of service risk through a kernel warning, and it can become a kernel crash on systems configured with panic_on_warn. No confidentiality or integrity impact is assigned because the observed primitive is a reachable warning rather than UAF, OOB access, or arbitrary write.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	WARNONLY BPF SIMPLEFIX LINUS  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

2. Signal breakdown

Conservative positive signals:

* +1 Local unprivileged trigger. The supplied context says a crafted user BTF can trigger the warning before map creation capability checks, so host-admin-equivalent privilege is not established for the trigger.

Paranoid additional signals:

* +1 Reliable kernel crash / strong DoS only under panic_on_warn-style deployments. The direct primitive is WARN_ON_ONCE, but such warnings can become fatal when the system is configured to panic on warnings.

Non-awarded material signals:

* +0 Real UAF not awarded. The patch shows uniqueness-state validation for nested BTF fields, not stale object use.
* +0 Memory corruption not awarded. No OOB write, UAF, arbitrary write, refcount mutation, type confusion, or controlled reclaim is established.
* +0 Confidentiality and integrity not awarded. The observed primitive is a reachable invariant warning, not a disclosure or modification primitive.
* +0 Strong LPE or weak LPE not awarded. No exploitation leverage beyond warning or panic_on_warn DoS is shown.
* +0 BPF high-control API not awarded. The attacker controls BTF metadata, but the patch does not establish control over exploitation-relevant memory layout, object lifetime, callback state, or kernel data contents.
* +0 Extra availability not awarded. The possible fatal result is the same warning-to-panic condition and is not counted twice.
* +0 Manual review escalation not awarded. This is validation-only WARN behavior without a concrete corruption or security-boundary primitive.

Negative signals:

* No host-admin penalty applied. The supplied evidence indicates the warning occurs before map creation capability checks.
* No race penalty applied. This is not a race.
* No niche-subsystem penalty applied. BPF privilege/configuration uncertainty is not used as a speculative negative penalty.

3. Reachability analysis

The trigger is local through crafted user-supplied BTF submitted to the BPF/BTF parsing path. The commit explicitly notes that duplicate unique special fields can reach btf_parse_fields and trigger WARN_ON_ONCE before map creation capability checks. That supports below-host-admin reachability for the warning path.

No network trigger is established. No namespace-scoped capability is needed or established for the relevant trigger, so NamespaceScopedPrivilege is NO rather than YES or UNKNOWN. There is no evidence of a required special device, rare hardware, boot mode, or timing race. The main deployment-dependent factor is whether WARN_ON_ONCE is fatal due to panic_on_warn or similar policy.

For BPF/XDP privilege separation: the issue is in BTF field validation, not XDP attach or device-bound program activation. The supplied evidence does not require successful privileged map creation or program attachment because the warning occurs before those checks.

4. Primitive and severity interpretation

The exact primitive is an input-validation logic error in BTF recursive field traversal. A fresh seen_mask was created for each recursive descent, so unique special fields at different nesting levels did not share one uniqueness state. This allowed duplicate fields to reach a later invariant check and trigger WARN_ON_ONCE.

This is not active structured UAF, fixed stale storage, repeated release, refcount mutation, RCU lifetime violation, or memory corruption. There is no first lifetime operation that may free an object and no second lifetime/refcount mutation through the same dangling reference.

PrimitiveClass is CLASS_C because the demonstrated behavior is invalid-state/WARN-based DoS behavior without an independently useful corruption primitive. The demonstrated consequence is a kernel warning, with possible kernel panic only on systems configured to panic on warnings. Speculative privilege escalation is not supported by the patch or supplied context. ImportantCandidate is NO because there is no Class A primitive and no unresolved Class B lifetime/corruption primitive. AutoDowngradeAllowed is YES because no meaningful corruption, ownership, authorization, or boundary-bypass primitive remains unresolved.

Likely operational severity is ordinary Moderate or Low-like depending on panic_on_warn policy.

5. One-sentence report phrase

A crafted user BTF with duplicate unique fields across nested structs can trigger WARN_ON_ONCE during BTF parsing before later capability checks, causing at most local DoS on systems where kernel warnings are fatal.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the patch supports a validation-only WARN_ON_ONCE path with no UAF, OOB access, arbitrary write, information leak, authorization bypass, or privilege-escalation primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: bpf: Preserve unique-field state across nested structs [ Upstream
Commit: cec97102d4147e18568c93946014c4c8ebf86fcf
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cec97102d4147e18568c93946014c4c8ebf86fcf

Changed files:
  kernel/bpf/btf.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=cec97102d4147e18568c93946014c4c8ebf86fcf

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

The original Linux kernel CVE announcement for CVE-2026-92515 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92515

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: 1
  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).