[CVE-2026-98599][MODERATE 7.0] bpf: Reject non-negative offsets in stack_slot_obj_get_spi() [ Upstream

[CVE-2026-98599][MODERATE 7.0] bpf: Reject non-negative offsets in stack_slot_obj_get_spi() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98599
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: Reject non-negative offsets in stack_slot_obj_get_spi() [ Upstream
Commit: 89a7241fc7ecc1b5e47c3f071081e314523b8d9d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=89a7241fc7ecc1b5e47c3f071081e314523b8d9d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98599
Analysis date: Sat, 24 Oct 2026 07:09:12 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A BPF verifier offset-validation flaw can pass an out-of-stack pointer to an effectful iterator kfunc as valid iterator state, creating a concrete verifier/runtime semantic-reinterpretation primitive.

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

The original Linux kernel CVE announcement for CVE-2026-98599 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98599

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.

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

CVE-2026-98599	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98599 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	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-20;CWE-681;CWE-823;*CWE-787;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.8';DESCR 'A BPF verifier validation flaw allows fp plus 0 to be treated as the same stack object index as the valid fp minus 8 slot because C division truncates toward zero. The verifier can therefore approve an iterator object at one address while an effectful iterator kfunc receives a pointer outside the BPF stack and may read or modify adjacent kernel memory as iterator state. For the CVSS the PR:L value reflects that an attacker needs local access to load an eligible BPF program, while delegated BPF access or a reduced capability service account need not represent full administrative control. This is a potential kernel memory corruption and privilege escalation issue rather than a demonstrated crash only condition, although practical exploitation depends on the available iterator kfunc and control over its operations. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 7.8 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the manual review requirement was applied. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	BPF SIMPLEFIX IMPROVEONLY LINUS  KPANIC INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 2.
* Conservative score: 5. Semantic-reinterpretation/manual-review safety floor applied: 2 -> 5.
* Raw paranoid score: 2.
* Paranoid score: 5. Same safety floor applied; no additional speculative corruption points.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 — Strong attacker-influenced semantic reinterpretation: `fp+0` passes validation as stack slot zero, corresponding to valid `fp-8`, while runtime supplies the actual out-of-stack `fp+0` pointer to an iterator kfunc.
* Floor 5 — The verifier/runtime check-to-use mismatch exposes memory outside the BPF stack as active iterator state; semantic reinterpretation must not be auto-closed.
* No privilege penalty: host-admin-equivalent privilege is not positively established.
* No separate OOB-write score: the commit supports effectful out-of-stack state consumption and possible modification, but does not identify a particular iterator kfunc, write width, payload, or destination.
* No LPE, confidentiality, crash, arbitrary-write, controlled-target, or practical-exploit bonus; none is demonstrated.
* B5-R does not apply: no retry-accumulated index is involved.
* B4 does not apply: this is verifier type/state validation, not a mandatory authorization DENY-to-ALLOW transition.

3. Reachability analysis

A local actor must load an eligible BPF program and invoke a compatible effectful iterator kfunc. The supplied material does not establish whether the complete load, verification, attachment, and execution chain works for an ordinary user, delegated capability holder, namespace-scoped actor, or only host administration. No remote path, retry race, special hardware, or namespace-complete trigger is shown.

4. Primitive and severity reading

The exact primitive is a verifier/runtime semantic mismatch: validation associates `fp+0` with the iterator at `fp-8`, then runtime processing treats memory beyond the BPF stack as structured iterator state. This is active structured-state reinterpretation, not a UAF or fixed stale buffer. The mismatch is proven; concrete OOB write mechanics, adjacent victim, disclosure, crash, and privilege escalation remain unresolved. It is CLASS_A under the semantic-reinterpretation rule, requiring Important review and prohibiting automatic downgrade.

5. One-sentence report phrase

A BPF verifier offset-validation flaw can pass an out-of-stack pointer to an effectful iterator kfunc as valid iterator state, creating a concrete verifier/runtime semantic-reinterpretation primitive.

6. Manual review advice

MANUAL CHECK REQUIRED

Identify reachable iterator kfuncs and trace their reads, writes, callbacks, and privilege requirements for the complete BPF execution chain.

7. Call-site confidence

Call-site confidence: medium

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

Patch: bpf: Reject non-negative offsets in stack_slot_obj_get_spi() [ Upstream
Commit: 89a7241fc7ecc1b5e47c3f071081e314523b8d9d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=89a7241fc7ecc1b5e47c3f071081e314523b8d9d

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=89a7241fc7ecc1b5e47c3f071081e314523b8d9d

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

The original Linux kernel CVE announcement for CVE-2026-98599 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98599

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:L/I:L/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: unknown
  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).