[CVE-2026-98059][LOW] bpf: Mark sched_process_wait argument as nullable [ Upstream

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

CVE: CVE-2026-98059
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: bpf: Mark sched_process_wait argument as nullable [ Upstream
Commit: bee862c79cb7e0e5c33b2df2e3a31d164705120d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bee862c79cb7e0e5c33b2df2e3a31d164705120d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98059
Analysis date: Fri, 25 Sep 2026 11:37:48 -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-2026-98059 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98059

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-2026-98059	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98059 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-693;BEST CVSS score: '5.5';DESCR 'A BPF verifier type annotation error treats the sched_process_wait argument as a trusted non nullable pointer even though it can be NULL for wait4(-1) and waitid(P_ALL). A local process that can load and attach a BPF raw tracepoint program can use an unchecked dereference and trigger a NULL pointer dereference in JITed BPF code when a wait for any child reaches the tracepoint. This can crash the kernel and cause denial of service. For the CVSS the PR:L value is used because reliable triggering requires local access to the BPF loading and raw tracepoint interface. The issue is not network reachable. The patch context demonstrates a NULL dereference only and does not provide evidence of use after free, out of bounds access, information disclosure, arbitrary write, or privilege escalation. Impact is denial of service only. Deployment exposure depends on whether untrusted users can load BPF programs and attach raw tracepoints under the local BPF policy.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	NULLPTR BPF SIMPLEFIX IMPROVEONLY LINUS 	YES	NO	checked

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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
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap was applied.

2. Signal breakdown

Positive signals:

* +1 Reliable kernel crash or strong DoS. The patch directly establishes that an unchecked dereference of a NULL trusted BTF pointer in JITed BPF code can cause a kernel NULL pointer dereference when sched_process_wait is reached.

Negative signals:

* No privilege penalty applied. The supplied evidence establishes that BPF program loading and raw tracepoint attachment are required, but it does not resolve whether the complete load, JIT, attach, and trigger sequence requires host-admin-equivalent privilege in the evaluated product.
* No race or timing penalty applied. The vulnerable sequence is deterministic after a suitable BPF program is attached and wait4(-1) or waitid(P_ALL) reaches the tracepoint.
* No niche-subsystem penalty applied. BPF policy and JIT availability are deployment-specific, but the supplied evidence does not establish a rare hardware or unusually inaccessible prerequisite.

Important non-awarded signals:

* No real UAF or post-lifetime object use is established.
* No controlled reclaim, object replacement, arbitrary write, OOB access, callback control, or refcount mutation is established.
* No confidentiality or integrity signal is awarded. The demonstrated primitive is a NULL pointer dereference only.
* No local-unprivileged-trigger point is awarded. The complete BPF load and raw tracepoint attachment privilege boundary is not established as reachable by an ordinary user.
* No remote-reachability point is awarded. Triggering requires a local BPF control-plane operation.
* No BPF high-control API point is awarded. The attacker controls BPF instructions, but there is no demonstrated attacker-controlled memory-layout, lifetime, ownership, or post-free corruption primitive.
* No additional availability point is awarded because the kernel crash is already counted once.

3. Reachability analysis

The triggering actor is a local process that can load a BPF program, enable JIT execution where applicable, and attach the program to the sched_process_wait raw tracepoint. The process then invokes wait4(-1) or waitid(P_ALL), or otherwise causes the attached tracepoint to execute with a NULL wo_pid argument.

The patch establishes the NULL argument condition and verifier acceptance of an unchecked dereference. It does not establish the privilege model for loading and attaching this raw tracepoint program in the evaluated deployment. On many systems, BPF loading and raw tracepoint attachment are restricted through CAP_BPF, CAP_SYS_ADMIN, perf-event policy, LSM policy, or distribution BPF restrictions. Therefore HostAdminRequired is UNKNOWN rather than YES or NO.

Namespace-scoped reachability is also UNKNOWN. The supplied patch does not show that all required stages, including BPF loading, JIT execution, raw tracepoint attachment, and triggering, can be completed using only attacker-created namespaces and namespace-scoped capabilities. No network device, XDP setup, special hardware, firmware, boot option, or prior host-created object is required by the demonstrated NULL dereference itself.

4. Primitive and severity interpretation

The exact primitive is an invalid NULL pointer dereference in JITed BPF code. The verifier incorrectly treats sched_process_wait argument zero as a non-null PTR_TO_BTF_ID and PTR_TRUSTED pointer, while do_wait can supply NULL for wait4(-1) and waitid(P_ALL). Trusted pointer loads lack fault protection, so an accepted unchecked dereference can fault in kernel context.

This is not an active structured stale-object issue, fixed stale storage issue, UAF, double release, refcount corruption, OOB access, or ownership violation. There is no first lifetime operation, no surviving dangling reference, and no second lifetime or refcount mutation. The demonstrated consequence is kernel crash or DoS.

The issue is CLASS_C because it is a crash-capable invalid-state and NULL-dereference bug without an independently useful kernel-corruption primitive. A stronger exploitation consequence is speculative and unsupported by the patch. ImportantCandidate is NO because no meaningful exploitation leverage beyond the crash is established. AutoDowngradeAllowed is YES because the demonstrated behavior is constrained to DoS and no unresolved corruption, authorization, ownership, or lifetime primitive remains.

Operational severity depends on local BPF policy. Systems that do not permit untrusted users to load and attach the relevant BPF programs have substantially reduced exposure. Systems delegating BPF raw tracepoint access to untrusted workloads should verify their policy and patch promptly.

5. One-sentence report phrase

A BPF verifier nullable-pointer annotation error allows an attached raw tracepoint program to dereference a NULL sched_process_wait argument and crash the local kernel when wait4(-1) or waitid(P_ALL) is executed.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Verify whether untrusted or delegated users can load JITed BPF programs and attach raw tracepoint programs to sched_process_wait under the product BPF, capability, perf-event, and LSM policy.

7. Call-site confidence

Call-site confidence: medium

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

Patch: bpf: Mark sched_process_wait argument as nullable [ Upstream
Commit: bee862c79cb7e0e5c33b2df2e3a31d164705120d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bee862c79cb7e0e5c33b2df2e3a31d164705120d

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=bee862c79cb7e0e5c33b2df2e3a31d164705120d

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

The original Linux kernel CVE announcement for CVE-2026-98059 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98059

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: Not available
  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: 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).