[CVE-2026-98075][MODERATE 7.0] bpf: reject BPF_PSEUDO_FUNC reference to the main program [ Upstream

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

CVE: CVE-2026-98075
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: bpf: reject BPF_PSEUDO_FUNC reference to the main program [ Upstream
Commit: 118212417ba0120d99f84154799f8880f07411f4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=118212417ba0120d99f84154799f8880f07411f4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98075
Analysis date: Mon, 28 Sep 2026 21:17:06 -0400
ActionableScore: 5
ActionableScore lower bound: unknown
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-98075 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98075

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-2026-98075	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98075 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-20;CWE-822;CWE-670;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'The BPF verifier can accept a BPF_PSEUDO_FUNC reference to the main program even though this reference is not rewritten to a real function address when no additional subprogram exists. A program can pass the resulting bogus function pointer to bpf_timer_set_callback or a similar callback interface and cause the kernel to perform an indirect call through an invalid address. The directly supported impact is a local kernel crash and denial of service. The invalid indirect call also creates a potential control flow primitive that may have greater confidentiality and integrity impact if the target address can be influenced reliably. For the CVSS the PR:L value is used because a local process must load the crafted BPF program and must have the BPF access granted by the system policy. The issue is not network reachable. The paranoid assessment uses AC:H and CIA:HHH because privilege escalation would require additional control over the unresolved address and kernel execution layout. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) 	MAYBE	BPF TIMER LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS	-	-	checked

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

ActionableScore=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 5
* Raw paranoid score: 4
* Paranoid score: 5
* Applied conservative safety floor: 3 -> 5 because a concrete semantic reinterpretation reaches an indirect kernel callback and requires exploitation-leverage review.
* Applied paranoid safety floor: 4 -> 5 for the same established active-execution primitive.
* The BPF privileged-control-plane cap does not reduce either result.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 Strong attacker-influenced semantic reinterpretation. The verifier treats a BPF_PSEUDO_FUNC relative reference as PTR_TO_FUNC, but without subprogram fixup the same value is later consumed as a native callback address.
* +1 Reliable kernel crash or strong DoS. The commit directly establishes an indirect function call through a bogus address.
* Paranoid +1 Active-execution consequence of the semantic mismatch. The unresolved value reaches callback dispatch, making architecture-specific control-flow leverage worth review beyond the demonstrated crash.
* No privilege penalty. Complete BPF loading and callback-trigger privilege requirements are unresolved, so host-admin privilege is not assumed.
* No remote-reachability point. The trigger requires loading and executing a crafted local BPF program.
* No UAF, controlled reclaim, arbitrary write, disclosure, or attacker-selected valid kernel target is demonstrated.
* No separate callback-control bonus was stacked with semantic reinterpretation because both describe the same indirect-call primitive.
* No extra Availability point was awarded because it would duplicate the same kernel crash.
* The previous paranoid CVSS C:H and I:H assumptions are not treated as proof of confidentiality or integrity impact.

3. Reachability analysis

The attacker must load a crafted BPF program containing a BPF_PSEUDO_FUNC reference to its main subprogram, arrange for that value to be accepted as PTR_TO_FUNC, and supply it to a callback consumer such as `bpf_timer_set_callback()`.

Modern deployments commonly restrict this through CAP_BPF, CAP_SYS_ADMIN, program-type restrictions, and the root-controlled unprivileged BPF policy. The supplied evidence does not resolve whether the complete load, map creation, timer setup, and callback execution sequence is available below host-admin-equivalent privilege. Therefore HostAdminRequired and NamespaceScopedPrivilege remain UNKNOWN, with neither a privilege bonus nor penalty.

No attachment to a network device, network input, special hardware, prior external setup, or timing race is established. The invalid-state sequence appears deterministic once an eligible program is accepted.

4. Primitive and severity interpretation

The exact primitive is semantic reinterpretation of an unresolved BPF pseudo-function reference as a native kernel function pointer, followed by an indirect callback invocation. This is not a UAF, stale-storage access, repeated release, or refcount mutation.

The patch-supported consequence is a call to a bogus address and a likely kernel fault or panic. The stronger unresolved question is whether the unrelocated immediate can be shaped on any supported JIT architecture into a useful executable target rather than merely a low, noncanonical, or otherwise immediately faulting address.

This is CLASS_A because an attacker-influenced representation reaches kernel callback dispatch under the wrong address semantics. It is not scored as demonstrated arbitrary control flow, arbitrary write, confidentiality loss, or privilege escalation. ImportantCandidate is YES because automatically treating the issue as ordinary crash-only input validation could discard a genuine control-flow primitive. AutoDowngradeAllowed is NO pending architecture-specific analysis of the unresolved value and callback invocation.

Likely operational severity is Actionable Moderate. Important severity would require evidence that the bogus callback address is meaningfully controllable or can reach a useful kernel execution target.

5. One-sentence report phrase

The BPF verifier can accept an unresolved main-program pseudo-function reference as a callback pointer, causing an indirect kernel call through a bogus address and requiring manual review to determine whether the result is limited to denial of service or provides useful control-flow influence.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Review the exact encoded value before and after verification, interpreter and JIT behavior on each affected architecture, callback invocation mechanics, and whether any configuration permits a below-host-admin attacker to load and trigger the program.

7. Call-site confidence

Call-site confidence: medium

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

Patch: bpf: reject BPF_PSEUDO_FUNC reference to the main program [ Upstream
Commit: 118212417ba0120d99f84154799f8880f07411f4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=118212417ba0120d99f84154799f8880f07411f4

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=118212417ba0120d99f84154799f8880f07411f4

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

The original Linux kernel CVE announcement for CVE-2026-98075 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98075

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:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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).